require 'search'
require 'select'
require 'undo'
require 'text_tests'

-- undo/redo by managing the sequence of events in the current session
-- based on https://github.com/akkartik/mu1/blob/master/edit/012-editor-undo.mu
-- Incredibly inefficient; we make a copy of lines on every single keystroke.
-- The hope here is that we're either editing small files or just reading large files.
-- TODO: highlight stuff inserted by any undo/redo operation
-- TODO: coalesce multiple similar operations
function record_undo_event(State, data)
  State.history[State.next_history] = data
  State.next_history = State.next_history+1
  for i=State.next_history,#State.history do
    State.history[i] = nil
  end
end
function undo_event(State)
  if State.next_history > 1 then
--?     print('moving to history', State.next_history-1)
    State.next_history = State.next_history-1
    local result = State.history[State.next_history]
    return result
  end
end
function redo_event(State)
  if State.next_history <= #State.history then
--?     print('restoring history', State.next_history+1)
    local result = State.history[State.next_history]
    State.next_history = State.next_history+1
    return result
  end
end
-- Copy all relevant global state.
-- Make copies of objects; the rest of the app may mutate them in place, but undo requires immutable histories.
function snapshot(State, s,e)
  -- Snapshot everything by default, but subset if requested.
  assert(s)
  if e == nil then
    e = s
  end
  assert(#State.lines > 0)
  if s < 1 then s = 1 end
  if s > #State.lines then s = #State.lines end
  if e < 1 then e = 1 end
  if e > #State.lines then e = #State.lines end
  -- compare with App.initialize_globals
  local event = {
    screen_top=deepcopy(State.screen_top1),
    selection=deepcopy(State.selection1),
    cursor=deepcopy(State.cursor1),
    lines={},
    start_line=s,
    end_line=e,
    -- no filename; undo history is cleared when filename changes
  }
  -- deep copy lines without cached stuff like text fragments
  for i=s,e do
    local line = State.lines[i]
    table.insert(event.lines, {data=line.data, dataB=line.dataB})
  end
  return event
end
function patch(lines, from, to)
--?   if #from.lines == 1 and #to.lines == 1 then
--?     assert(from.start_line == from.end_line)
--?     assert(to.start_line == to.end_line)
--?     assert(from.start_line == to.start_line)
--?     lines[from.start_line] = to.lines[1]
--?     return
--?   end
  assert(from.start_line == to.start_line)
  for i=from.end_line,from.start_line,-1 do
    table.remove(lines, i)
  end
  assert(#to.lines == to.end_line-to.start_line+1)
  for i=1,#to.lines do
    table.insert(lines, to.start_line+i-1, to.lines[i])
  end
end
function patch_placeholders(line_cache, from, to)
  assert(from.start_line == to.start_line)
  for i=from.end_line,from.start_line,-1 do
    table.remove(line_cache, i)
  end
  assert(#to.lines == to.end_line-to.start_line+1)
  for i=1,#to.lines do
    table.insert(line_cache, to.start_line+i-1, {})
  end
end
-- https://stackoverflow.com/questions/640642/how-do-you-copy-a-lua-table-by-value/26367080#26367080
function deepcopy(obj, seen)
  if type(obj) ~= 'table' then return obj end
  if seen and seen[obj] then return seen[obj] end
  local s = seen or {}
  local result = setmetatable({}, getmetatable(obj))
  s[obj] = result
  for k,v in pairs(obj) do
    result[deepcopy(k, s)] = deepcopy(v, s)
  end
  return result
end
function minmax(a, b)
  return math.min(a,b), math.max(a,b)
end

-- major tests for text editing flows
function test_initial_state()
  io.write('\ntest_initial_state')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{}
  Text.redraw_all(Editor_state)
  edit.draw(Editor_state)
  check_eq(#Editor_state.lines, 1, 'F - test_initial_state/#lines')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_initial_state/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_initial_state/cursor:pos')
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_initial_state/screen_top:line')
  check_eq(Editor_state.screen_top1.pos, 1, 'F - test_initial_state/screen_top:pos')
end
function test_backspace_from_start_of_final_line()
  io.write('\ntest_backspace_from_start_of_final_line')
  -- display final line of text with cursor at start of it
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def'}
  Editor_state.screen_top1 = {line=2, pos=1}
  Editor_state.cursor1 = {line=2, pos=1}
  Text.redraw_all(Editor_state)
  -- backspace scrolls up
  edit.run_after_keychord(Editor_state, 'backspace')
  check_eq(#Editor_state.lines, 1, 'F - test_backspace_from_start_of_final_line/#lines')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_backspace_from_start_of_final_line/cursor')
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_backspace_from_start_of_final_line/screen_top')
end
function test_insert_first_character()
  io.write('\ntest_insert_first_character')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{}
  Text.redraw_all(Editor_state)
  edit.draw(Editor_state)
  edit.run_after_textinput(Editor_state, 'a')
  local y = Editor_state.top
  App.screen.check(y, 'a', 'F - test_insert_first_character/screen:1')
end
function test_press_ctrl()
  io.write('\ntest_press_ctrl')
  -- press ctrl while the cursor is on text
  App.screen.init{width=50, height=80}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{''}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.run_after_keychord(Editor_state, 'C-m')
end
function test_move_left()
  io.write('\ntest_move_left')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'a'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=2}
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'left')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_move_left')
end
function test_move_right()
  io.write('\ntest_move_right')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'a'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'right')
  check_eq(Editor_state.cursor1.pos, 2, 'F - test_move_right')
end
function test_move_left_to_previous_line()
  io.write('\ntest_move_left_to_previous_line')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'left')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_move_left_to_previous_line/line')
  check_eq(Editor_state.cursor1.pos, 4, 'F - test_move_left_to_previous_line/pos')  -- past end of line
end
function test_move_right_to_next_line()
  io.write('\ntest_move_right_to_next_line')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=4}  -- past end of line
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'right')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_move_right_to_next_line/line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_move_right_to_next_line/pos')
end
function test_move_to_start_of_word()
  io.write('\ntest_move_to_start_of_word')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=3}
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'M-left')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_move_to_start_of_word')
end
function test_move_to_start_of_previous_word()
  io.write('\ntest_move_to_start_of_previous_word')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=4}  -- at the space between words
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'M-left')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_move_to_start_of_previous_word')
end
function test_skip_to_previous_word()
  io.write('\ntest_skip_to_previous_word')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=5}  -- at the start of second word
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'M-left')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_skip_to_previous_word')
end
function test_skip_past_tab_to_previous_word()
  io.write('\ntest_skip_past_tab_to_previous_word')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def\tghi'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=10}  -- within third word
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'M-left')
  check_eq(Editor_state.cursor1.pos, 9, 'F - test_skip_past_tab_to_previous_word')
end
function test_skip_multiple_spaces_to_previous_word()
  io.write('\ntest_skip_multiple_spaces_to_previous_word')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc  def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=6}  -- at the start of second word
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'M-left')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_skip_multiple_spaces_to_previous_word')
end
function test_move_to_start_of_word_on_previous_line()
  io.write('\ntest_move_to_start_of_word_on_previous_line')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def', 'ghi'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'M-left')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_move_to_start_of_word_on_previous_line/line')
  check_eq(Editor_state.cursor1.pos, 5, 'F - test_move_to_start_of_word_on_previous_line/pos')
end
function test_move_past_end_of_word()
  io.write('\ntest_move_past_end_of_word')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'M-right')
  check_eq(Editor_state.cursor1.pos, 4, 'F - test_move_past_end_of_word')
end
function test_skip_to_next_word()
  io.write('\ntest_skip_to_next_word')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=4}  -- at the space between words
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'M-right')
  check_eq(Editor_state.cursor1.pos, 8, 'F - test_skip_to_next_word')
end
function test_skip_past_tab_to_next_word()
  io.write('\ntest_skip_past_tab_to_next_word')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc\tdef'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}  -- at the space between words
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'M-right')
  check_eq(Editor_state.cursor1.pos, 4, 'F - test_skip_past_tab_to_next_word')
end
function test_skip_multiple_spaces_to_next_word()
  io.write('\ntest_skip_multiple_spaces_to_next_word')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc  def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=4}  -- at the start of second word
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'M-right')
  check_eq(Editor_state.cursor1.pos, 9, 'F - test_skip_multiple_spaces_to_next_word')
end
function test_move_past_end_of_word_on_next_line()
  io.write('\ntest_move_past_end_of_word_on_next_line')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def', 'ghi'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=8}
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'M-right')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_move_past_end_of_word_on_next_line/line')
  check_eq(Editor_state.cursor1.pos, 4, 'F - test_move_past_end_of_word_on_next_line/pos')
end
function test_click_with_mouse()
  io.write('\ntest_click_with_mouse')
  -- display two lines with cursor on one of them
  App.screen.init{width=50, height=80}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  -- click on the other line
  edit.draw(Editor_state)
  edit.run_after_mouse_click(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
  -- cursor moves
  check_eq(Editor_state.cursor1.line, 1, 'F - test_click_with_mouse/cursor:line')
end
function test_click_with_mouse_to_left_of_line()
  io.write('\ntest_click_with_mouse_to_left_of_line')
  -- display a line with the cursor in the middle
  App.screen.init{width=50, height=80}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=3}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  -- click to the left of the line
  edit.draw(Editor_state)
  edit.run_after_mouse_click(Editor_state, Editor_state.left-4,Editor_state.top+5, 1)
  -- cursor moves to start of line
  check_eq(Editor_state.cursor1.line, 1, 'F - test_click_with_mouse_to_left_of_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_click_with_mouse_to_left_of_line/cursor:pos')
end
function test_click_with_mouse_takes_margins_into_account()
  io.write('\ntest_click_with_mouse_takes_margins_into_account')
  -- display two lines with cursor on one of them
  App.screen.init{width=100, height=80}
  Editor_state = edit.initialize_test_state()
  Editor_state.left = 50  -- occupy only right side of screen
  Editor_state.lines = load_array{'abc', 'def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  -- click on the other line
  edit.draw(Editor_state)
  edit.run_after_mouse_click(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
  -- cursor moves
  check_eq(Editor_state.cursor1.line, 1, 'F - test_click_with_mouse_takes_margins_into_account/cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'F - test_click_with_mouse_takes_margins_into_account/cursor:pos')
end
function test_click_with_mouse_on_empty_line()
  io.write('\ntest_click_with_mouse_on_empty_line')
  -- display two lines with the first one empty
  App.screen.init{width=50, height=80}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'', 'def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  -- click on the empty line
  edit.draw(Editor_state)
  edit.run_after_mouse_click(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
  -- cursor moves
  check_eq(Editor_state.cursor1.line, 1, 'F - test_click_with_mouse_on_empty_line/cursor')
end
function test_draw_text()
  io.write('\ntest_draw_text')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_draw_text/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_draw_text/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'F - test_draw_text/screen:3')
end
function test_draw_wrapping_text()
  io.write('\ntest_draw_wrapping_text')
  App.screen.init{width=50, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'defgh', 'xyz'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_draw_wrapping_text/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'de', 'F - test_draw_wrapping_text/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'fgh', 'F - test_draw_wrapping_text/screen:3')
end
function test_draw_word_wrapping_text()
  io.write('\ntest_draw_word_wrapping_text')
  App.screen.init{width=60, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def ghi', 'jkl'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'abc ', 'F - test_draw_word_wrapping_text/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def ', 'F - test_draw_word_wrapping_text/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'F - test_draw_word_wrapping_text/screen:3')
end
function test_click_with_mouse_on_wrapping_line()
  io.write('\ntest_click_with_mouse_on_wrapping_line')
  -- display two lines with cursor on one of them
  App.screen.init{width=50, height=80}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def ghi jkl mno pqr stu'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=20}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  -- click on the other line
  edit.draw(Editor_state)
  edit.run_after_mouse_click(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
  -- cursor moves
  check_eq(Editor_state.cursor1.line, 1, 'F - test_click_with_mouse_on_wrapping_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'F - test_click_with_mouse_on_wrapping_line/cursor:pos')
end
function test_click_with_mouse_on_wrapping_line_takes_margins_into_account()
  io.write('\ntest_click_with_mouse_on_wrapping_line_takes_margins_into_account')
  -- display two lines with cursor on one of them
  App.screen.init{width=100, height=80}
  Editor_state = edit.initialize_test_state()
  Editor_state.left = 50  -- occupy only right side of screen
  Editor_state.lines = load_array{'abc def ghi jkl mno pqr stu'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=20}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  -- click on the other line
  edit.draw(Editor_state)
  edit.run_after_mouse_click(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
  -- cursor moves
  check_eq(Editor_state.cursor1.line, 1, 'F - test_click_with_mouse_on_wrapping_line_takes_margins_into_account/cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'F - test_click_with_mouse_on_wrapping_line_takes_margins_into_account/cursor:pos')
end
function test_draw_text_wrapping_within_word()
  -- arrange a screen line that needs to be split within a word
  io.write('\ntest_draw_text_wrapping_within_word')
  App.screen.init{width=60, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abcd e fghijk', 'xyz'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'abcd ', 'F - test_draw_text_wrapping_within_word/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'e fgh', 'F - test_draw_text_wrapping_within_word/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ijk', 'F - test_draw_text_wrapping_within_word/screen:3')
end
function test_draw_wrapping_text_containing_non_ascii()
  -- draw a long line containing non-ASCII
  io.write('\ntest_draw_wrapping_text_containing_non_ascii')
  App.screen.init{width=60, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'madam I’m adam', 'xyz'}  -- notice the non-ASCII apostrophe
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'mad', 'F - test_draw_wrapping_text_containing_non_ascii/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'am I', 'F - test_draw_wrapping_text_containing_non_ascii/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, '’m a', 'F - test_draw_wrapping_text_containing_non_ascii/screen:3')
end
function test_click_on_wrapping_line()
  io.write('\ntest_click_on_wrapping_line')
  -- display a wrapping line
  App.screen.init{width=75, height=80}
  Editor_state = edit.initialize_test_state()
                               --  12345678901234
  Editor_state.lines = load_array{"madam I'm adam"}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'madam ', 'F - test_click_on_wrapping_line/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, "I'm ad", 'F - test_click_on_wrapping_line/baseline/screen:2')
  y = y + Editor_state.line_height
  -- click past end of second screen line
  edit.run_after_mouse_click(Editor_state, App.screen.width-2,y-2, 1)
  -- cursor moves to end of screen line
  check_eq(Editor_state.cursor1.line, 1, 'F - test_click_on_wrapping_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 12, 'F - test_click_on_wrapping_line/cursor:pos')
end
function test_click_on_wrapping_line_rendered_from_partway_at_top_of_screen()
  io.write('\ntest_click_on_wrapping_line_rendered_from_partway_at_top_of_screen')
  -- display a wrapping line from its second screen line
  App.screen.init{width=75, height=80}
  Editor_state = edit.initialize_test_state()
                               --  12345678901234
  Editor_state.lines = load_array{"madam I'm adam"}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=8}
  Editor_state.screen_top1 = {line=1, pos=7}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, "I'm ad", 'F - test_click_on_wrapping_line_rendered_from_partway_at_top_of_screen/baseline/screen:2')
  y = y + Editor_state.line_height
  -- click past end of second screen line
  edit.run_after_mouse_click(Editor_state, App.screen.width-2,y-2, 1)
  -- cursor moves to end of screen line
  check_eq(Editor_state.cursor1.line, 1, 'F - test_click_on_wrapping_line_rendered_from_partway_at_top_of_screen/cursor:line')
  check_eq(Editor_state.cursor1.pos, 12, 'F - test_click_on_wrapping_line_rendered_from_partway_at_top_of_screen/cursor:pos')
end
function test_click_past_end_of_wrapping_line()
  io.write('\ntest_click_past_end_of_wrapping_line')
  -- display a wrapping line
  App.screen.init{width=75, height=80}
  Editor_state = edit.initialize_test_state()
                               --  12345678901234
  Editor_state.lines = load_array{"madam I'm adam"}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'madam ', 'F - test_click_past_end_of_wrapping_line/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, "I'm ad", 'F - test_click_past_end_of_wrapping_line/baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'am', 'F - test_click_past_end_of_wrapping_line/baseline/screen:3')
  y = y + Editor_state.line_height
  -- click past the end of it
  edit.run_after_mouse_click(Editor_state, App.screen.width-2,y-2, 1)
  -- cursor moves to end of line
  check_eq(Editor_state.cursor1.pos, 15, 'F - test_click_past_end_of_wrapping_line/cursor')  -- one more than the number of UTF-8 code-points
end
function test_click_past_end_of_wrapping_line_containing_non_ascii()
  io.write('\ntest_click_past_end_of_wrapping_line_containing_non_ascii')
  -- display a wrapping line containing non-ASCII
  App.screen.init{width=75, height=80}
  Editor_state = edit.initialize_test_state()
                               --  12345678901234
  Editor_state.lines = load_array{'madam I’m adam'}  -- notice the non-ASCII apostrophe
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'madam ', 'F - test_click_past_end_of_wrapping_line_containing_non_ascii/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'I’m ad', 'F - test_click_past_end_of_wrapping_line_containing_non_ascii/baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'am', 'F - test_click_past_end_of_wrapping_line_containing_non_ascii/baseline/screen:3')
  y = y + Editor_state.line_height
  -- click past the end of it
  edit.run_after_mouse_click(Editor_state, App.screen.width-2,y-2, 1)
  -- cursor moves to end of line
  check_eq(Editor_state.cursor1.pos, 15, 'F - test_click_past_end_of_wrapping_line_containing_non_ascii/cursor')  -- one more than the number of UTF-8 code-points
end
function test_click_past_end_of_word_wrapping_line()
  io.write('\ntest_click_past_end_of_word_wrapping_line')
  -- display a long line wrapping at a word boundary on a screen of more realistic length
  App.screen.init{width=160, height=80}
  Editor_state = edit.initialize_test_state()
                                -- 0        1         2
                                -- 123456789012345678901
  Editor_state.lines = load_array{'the quick brown fox jumped over the lazy dog'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'the quick brown fox ', 'F - test_click_past_end_of_word_wrapping_line/baseline/screen:1')
  y = y + Editor_state.line_height
  -- click past the end of the screen line
  edit.run_after_mouse_click(Editor_state, App.screen.width-2,y-2, 1)
  -- cursor moves to end of screen line
  check_eq(Editor_state.cursor1.pos, 20, 'F - test_click_past_end_of_word_wrapping_line/cursor')
end
function test_edit_wrapping_text()
  io.write('\ntest_edit_wrapping_text')
  App.screen.init{width=50, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'xyz'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=4}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  edit.run_after_textinput(Editor_state, 'g')
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_edit_wrapping_text/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'de', 'F - test_edit_wrapping_text/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'fg', 'F - test_edit_wrapping_text/screen:3')
end
function test_insert_newline()
  io.write('\ntest_insert_newline')
  -- display a few lines
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=2}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_insert_newline/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_insert_newline/baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'F - test_insert_newline/baseline/screen:3')
  -- hitting the enter key splits the line
  edit.run_after_keychord(Editor_state, 'return')
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_insert_newline/screen_top')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_insert_newline/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_insert_newline/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'a', 'F - test_insert_newline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'bc', 'F - test_insert_newline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_insert_newline/screen:3')
end
function test_insert_newline_at_start_of_line()
  io.write('\ntest_insert_newline_at_start_of_line')
  -- display a line
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  -- hitting the enter key splits the line
  edit.run_after_keychord(Editor_state, 'return')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_insert_newline_at_start_of_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_insert_newline_at_start_of_line/cursor:pos')
  check_eq(Editor_state.lines[1].data, '', 'F - test_insert_newline_at_start_of_line/data:1')
  check_eq(Editor_state.lines[2].data, 'abc', 'F - test_insert_newline_at_start_of_line/data:2')
end
function test_insert_from_clipboard()
  io.write('\ntest_insert_from_clipboard')
  -- display a few lines
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=2}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_insert_from_clipboard/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_insert_from_clipboard/baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'F - test_insert_from_clipboard/baseline/screen:3')
  -- paste some text including a newline, check that new line is created
  App.clipboard = 'xy\nz'
  edit.run_after_keychord(Editor_state, 'C-v')
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_insert_from_clipboard/screen_top')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_insert_from_clipboard/cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'F - test_insert_from_clipboard/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'axy', 'F - test_insert_from_clipboard/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'zbc', 'F - test_insert_from_clipboard/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_insert_from_clipboard/screen:3')
end
function test_move_cursor_using_mouse()
  io.write('\ntest_move_cursor_using_mouse')
  App.screen.init{width=50, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'xyz'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)  -- populate line_cache.starty for each line Editor_state.line_cache
  edit.run_after_mouse_press(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
  check_eq(Editor_state.cursor1.line, 1, 'F - test_move_cursor_using_mouse/cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'F - test_move_cursor_using_mouse/cursor:pos')
end
function test_pagedown()
  io.write('\ntest_pagedown')
  App.screen.init{width=120, height=45}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  -- initially the first two lines are displayed
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_pagedown/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_pagedown/baseline/screen:2')
  -- after pagedown the bottom line becomes the top
  edit.run_after_keychord(Editor_state, 'pagedown')
  check_eq(Editor_state.screen_top1.line, 2, 'F - test_pagedown/screen_top')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_pagedown/cursor')
  y = Editor_state.top
  App.screen.check(y, 'def', 'F - test_pagedown/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'F - test_pagedown/screen:2')
end
function test_pagedown_can_start_from_middle_of_long_wrapping_line()
  io.write('\ntest_pagedown_can_start_from_middle_of_long_wrapping_line')
  -- draw a few lines starting from a very long wrapping line
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def ghi jkl mno pqr stu vwx yza bcd efg hij', 'XYZ'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=2}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'abc ', 'F - test_pagedown_can_start_from_middle_of_long_wrapping_line/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def ', 'F - test_pagedown_can_start_from_middle_of_long_wrapping_line/baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi ', 'F - test_pagedown_can_start_from_middle_of_long_wrapping_line/baseline/screen:3')
  -- after pagedown we scroll down the very long wrapping line
  edit.run_after_keychord(Editor_state, 'pagedown')
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_pagedown_can_start_from_middle_of_long_wrapping_line/screen_top:line')
  check_eq(Editor_state.screen_top1.pos, 9, 'F - test_pagedown_can_start_from_middle_of_long_wrapping_line/screen_top:pos')
  y = Editor_state.top
  App.screen.check(y, 'ghi ', 'F - test_pagedown_can_start_from_middle_of_long_wrapping_line/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl ', 'F - test_pagedown_can_start_from_middle_of_long_wrapping_line/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno ', 'F - test_pagedown_can_start_from_middle_of_long_wrapping_line/screen:3')
end
function test_pagedown_never_moves_up()
  io.write('\ntest_pagedown_never_moves_up')
  -- draw the final screen line of a wrapping line
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def ghi'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=9}
  Editor_state.screen_top1 = {line=1, pos=9}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  -- pagedown makes no change
  edit.run_after_keychord(Editor_state, 'pagedown')
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_pagedown_never_moves_up/screen_top:line')
  check_eq(Editor_state.screen_top1.pos, 9, 'F - test_pagedown_never_moves_up/screen_top:pos')
end
function test_down_arrow_moves_cursor()
  io.write('\ntest_down_arrow_moves_cursor')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  -- initially the first three lines are displayed
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_down_arrow_moves_cursor/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_down_arrow_moves_cursor/baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'F - test_down_arrow_moves_cursor/baseline/screen:3')
  -- after hitting the down arrow, the cursor moves down by 1 line
  edit.run_after_keychord(Editor_state, 'down')
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_down_arrow_moves_cursor/screen_top')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_down_arrow_moves_cursor/cursor')
  -- the screen is unchanged
  y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_down_arrow_moves_cursor/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_down_arrow_moves_cursor/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'F - test_down_arrow_moves_cursor/screen:3')
end
function test_down_arrow_scrolls_down_by_one_line()
  io.write('\ntest_down_arrow_scrolls_down_by_one_line')
  -- display the first three lines with the cursor on the bottom line
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=3, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_down_arrow_scrolls_down_by_one_line/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_line/baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'F - test_down_arrow_scrolls_down_by_one_line/baseline/screen:3')
  -- after hitting the down arrow the screen scrolls down by one line
  edit.run_after_keychord(Editor_state, 'down')
  check_eq(Editor_state.screen_top1.line, 2, 'F - test_down_arrow_scrolls_down_by_one_line/screen_top')
  check_eq(Editor_state.cursor1.line, 4, 'F - test_down_arrow_scrolls_down_by_one_line/cursor')
  y = Editor_state.top
  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_line/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'F - test_down_arrow_scrolls_down_by_one_line/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'F - test_down_arrow_scrolls_down_by_one_line/screen:3')
end
function test_down_arrow_scrolls_down_by_one_screen_line()
  io.write('\ntest_down_arrow_scrolls_down_by_one_screen_line')
  -- display the first three lines with the cursor on the bottom line
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi jkl', 'mno'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=3, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_down_arrow_scrolls_down_by_one_screen_line/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_screen_line/baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi ', 'F - test_down_arrow_scrolls_down_by_one_screen_line/baseline/screen:3')  -- line wrapping includes trailing whitespace
  -- after hitting the down arrow the screen scrolls down by one line
  edit.run_after_keychord(Editor_state, 'down')
  check_eq(Editor_state.screen_top1.line, 2, 'F - test_down_arrow_scrolls_down_by_one_screen_line/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'F - test_down_arrow_scrolls_down_by_one_screen_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 5, 'F - test_down_arrow_scrolls_down_by_one_screen_line/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_screen_line/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi ', 'F - test_down_arrow_scrolls_down_by_one_screen_line/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'F - test_down_arrow_scrolls_down_by_one_screen_line/screen:3')
end
function test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word()
  io.write('\ntest_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word')
  -- display the first three lines with the cursor on the bottom line
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghijkl', 'mno'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=3, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghij', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/baseline/screen:3')
  -- after hitting the down arrow the screen scrolls down by one line
  edit.run_after_keychord(Editor_state, 'down')
  check_eq(Editor_state.screen_top1.line, 2, 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/cursor:line')
  check_eq(Editor_state.cursor1.pos, 5, 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghij', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'kl', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/screen:3')
end
function test_page_down_followed_by_down_arrow_does_not_scroll_screen_up()
  io.write('\ntest_page_down_followed_by_down_arrow_does_not_scroll_screen_up')
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghijkl', 'mno'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=3, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghij', 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/baseline/screen:3')
  -- after hitting pagedown the screen scrolls down to start of a long line
  edit.run_after_keychord(Editor_state, 'pagedown')
  check_eq(Editor_state.screen_top1.line, 3, 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/baseline2/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/baseline2/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/baseline2/cursor:pos')
  -- after hitting down arrow the screen doesn't scroll down further, and certainly doesn't scroll up
  edit.run_after_keychord(Editor_state, 'down')
  check_eq(Editor_state.screen_top1.line, 3, 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/cursor:line')
  check_eq(Editor_state.cursor1.pos, 5, 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'ghij', 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'kl', 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno', 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/screen:3')
end
function test_up_arrow_moves_cursor()
  io.write('\ntest_up_arrow_moves_cursor')
  -- display the first 3 lines with the cursor on the bottom line
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=3, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_up_arrow_moves_cursor/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_up_arrow_moves_cursor/baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'F - test_up_arrow_moves_cursor/baseline/screen:3')
  -- after hitting the up arrow the cursor moves up by 1 line
  edit.run_after_keychord(Editor_state, 'up')
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_up_arrow_moves_cursor/screen_top')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_up_arrow_moves_cursor/cursor')
  -- the screen is unchanged
  y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_up_arrow_moves_cursor/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_up_arrow_moves_cursor/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'F - test_up_arrow_moves_cursor/screen:3')
end
function test_up_arrow_scrolls_up_by_one_line()
  io.write('\ntest_up_arrow_scrolls_up_by_one_line')
  -- display the lines 2/3/4 with the cursor on line 2
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=2, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'def', 'F - test_up_arrow_scrolls_up_by_one_line/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'F - test_up_arrow_scrolls_up_by_one_line/baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'F - test_up_arrow_scrolls_up_by_one_line/baseline/screen:3')
  -- after hitting the up arrow the screen scrolls up by one line
  edit.run_after_keychord(Editor_state, 'up')
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_up_arrow_scrolls_up_by_one_line/screen_top')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_up_arrow_scrolls_up_by_one_line/cursor')
  y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_up_arrow_scrolls_up_by_one_line/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_up_arrow_scrolls_up_by_one_line/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'F - test_up_arrow_scrolls_up_by_one_line/screen:3')
end
function test_up_arrow_scrolls_up_by_one_screen_line()
  io.write('\ntest_up_arrow_scrolls_up_by_one_screen_line')
  -- display lines starting from second screen line of a line
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi jkl', 'mno'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=3, pos=6}
  Editor_state.screen_top1 = {line=3, pos=5}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'jkl', 'F - test_up_arrow_scrolls_up_by_one_screen_line/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno', 'F - test_up_arrow_scrolls_up_by_one_screen_line/baseline/screen:2')
  -- after hitting the up arrow the screen scrolls up to first screen line
  edit.run_after_keychord(Editor_state, 'up')
  y = Editor_state.top
  App.screen.check(y, 'ghi ', 'F - test_up_arrow_scrolls_up_by_one_screen_line/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'F - test_up_arrow_scrolls_up_by_one_screen_line/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno', 'F - test_up_arrow_scrolls_up_by_one_screen_line/screen:3')
  check_eq(Editor_state.screen_top1.line, 3, 'F - test_up_arrow_scrolls_up_by_one_screen_line/screen_top')
  check_eq(Editor_state.screen_top1.pos, 1, 'F - test_up_arrow_scrolls_up_by_one_screen_line/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'F - test_up_arrow_scrolls_up_by_one_screen_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_up_arrow_scrolls_up_by_one_screen_line/cursor:pos')
end
function test_up_arrow_scrolls_up_to_final_screen_line()
  io.write('\ntest_up_arrow_scrolls_up_to_final_screen_line')
  -- display lines starting just after a long line
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def', 'ghi', 'jkl', 'mno'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=2, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'ghi', 'F - test_up_arrow_scrolls_up_to_final_screen_line/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'F - test_up_arrow_scrolls_up_to_final_screen_line/baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno', 'F - test_up_arrow_scrolls_up_to_final_screen_line/baseline/screen:3')
  -- after hitting the up arrow the screen scrolls up to final screen line of previous line
  edit.run_after_keychord(Editor_state, 'up')
  y = Editor_state.top
  App.screen.check(y, 'def', 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen:3')
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen_top')
  check_eq(Editor_state.screen_top1.pos, 5, 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen_top')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_up_arrow_scrolls_up_to_final_screen_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 5, 'F - test_up_arrow_scrolls_up_to_final_screen_line/cursor:pos')
end
function test_up_arrow_scrolls_up_to_empty_line()
  io.write('\ntest_up_arrow_scrolls_up_to_empty_line')
  -- display a screenful of text with an empty line just above it outside the screen
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'', 'abc', 'def', 'ghi', 'jkl'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=2, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_up_arrow_scrolls_up_to_empty_line/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_up_arrow_scrolls_up_to_empty_line/baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'F - test_up_arrow_scrolls_up_to_empty_line/baseline/screen:3')
  -- after hitting the up arrow the screen scrolls up by one line
  edit.run_after_keychord(Editor_state, 'up')
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_up_arrow_scrolls_up_to_empty_line/screen_top')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_up_arrow_scrolls_up_to_empty_line/cursor')
  y = Editor_state.top
  -- empty first line
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'F - test_up_arrow_scrolls_up_to_empty_line/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_up_arrow_scrolls_up_to_empty_line/screen:3')
end
function test_pageup()
  io.write('\ntest_pageup')
  App.screen.init{width=120, height=45}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=2, pos=1}
  Editor_state.screen_bottom1 = {}
  -- initially the last two lines are displayed
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'def', 'F - test_pageup/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'F - test_pageup/baseline/screen:2')
  -- after pageup the cursor goes to first line
  edit.run_after_keychord(Editor_state, 'pageup')
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_pageup/screen_top')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_pageup/cursor')
  y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_pageup/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_pageup/screen:2')
end
function test_pageup_scrolls_up_by_screen_line()
  io.write('\ntest_pageup_scrolls_up_by_screen_line')
  -- display the first three lines with the cursor on the bottom line
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def', 'ghi', 'jkl', 'mno'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=2, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'ghi', 'F - test_pageup_scrolls_up_by_screen_line/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'F - test_pageup_scrolls_up_by_screen_line/baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno', 'F - test_pageup_scrolls_up_by_screen_line/baseline/screen:3')  -- line wrapping includes trailing whitespace
  -- after hitting the page-up key the screen scrolls up to top
  edit.run_after_keychord(Editor_state, 'pageup')
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_pageup_scrolls_up_by_screen_line/screen_top')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_pageup_scrolls_up_by_screen_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_pageup_scrolls_up_by_screen_line/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'abc ', 'F - test_pageup_scrolls_up_by_screen_line/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_pageup_scrolls_up_by_screen_line/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'F - test_pageup_scrolls_up_by_screen_line/screen:3')
end
function test_pageup_scrolls_up_from_middle_screen_line()
  io.write('\ntest_pageup_scrolls_up_from_middle_screen_line')
  -- display a few lines starting from the middle of a line (Editor_state.cursor1.pos > 1)
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def', 'ghi jkl', 'mno'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=5}
  Editor_state.screen_top1 = {line=2, pos=5}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'jkl', 'F - test_pageup_scrolls_up_from_middle_screen_line/baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno', 'F - test_pageup_scrolls_up_from_middle_screen_line/baseline/screen:3')  -- line wrapping includes trailing whitespace
  -- after hitting the page-up key the screen scrolls up to top
  edit.run_after_keychord(Editor_state, 'pageup')
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_pageup_scrolls_up_from_middle_screen_line/screen_top')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_pageup_scrolls_up_from_middle_screen_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_pageup_scrolls_up_from_middle_screen_line/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'abc ', 'F - test_pageup_scrolls_up_from_middle_screen_line/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_pageup_scrolls_up_from_middle_screen_line/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi ', 'F - test_pageup_scrolls_up_from_middle_screen_line/screen:3')
end
function test_enter_on_bottom_line_scrolls_down()
  io.write('\ntest_enter_on_bottom_line_scrolls_down')
  -- display a few lines with cursor on bottom line
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=3, pos=2}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_enter_on_bottom_line_scrolls_down/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_enter_on_bottom_line_scrolls_down/baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'F - test_enter_on_bottom_line_scrolls_down/baseline/screen:3')
  -- after hitting the enter key the screen scrolls down
  edit.run_after_keychord(Editor_state, 'return')
  check_eq(Editor_state.screen_top1.line, 2, 'F - test_enter_on_bottom_line_scrolls_down/screen_top')
  check_eq(Editor_state.cursor1.line, 4, 'F - test_enter_on_bottom_line_scrolls_down/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_enter_on_bottom_line_scrolls_down/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'def', 'F - test_enter_on_bottom_line_scrolls_down/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'g', 'F - test_enter_on_bottom_line_scrolls_down/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'hi', 'F - test_enter_on_bottom_line_scrolls_down/screen:3')
end
function test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom()
  io.write('\ntest_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom')
  -- display just the bottom line on screen
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=4, pos=2}
  Editor_state.screen_top1 = {line=4, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'jkl', 'F - test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom/baseline/screen:1')
  -- after hitting the enter key the screen does not scroll down
  edit.run_after_keychord(Editor_state, 'return')
  check_eq(Editor_state.screen_top1.line, 4, 'F - test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom/screen_top')
  check_eq(Editor_state.cursor1.line, 5, 'F - test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'j', 'F - test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'kl', 'F - test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom/screen:2')
end
function test_inserting_text_on_final_line_avoids_scrolling_down_when_not_at_bottom()
  io.write('\ntest_inserting_text_on_final_line_avoids_scrolling_down_when_not_at_bottom')
  -- display just an empty bottom line on screen
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', ''}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=2, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  -- after hitting the inserting_text key the screen does not scroll down
  edit.run_after_textinput(Editor_state, 'a')
  check_eq(Editor_state.screen_top1.line, 2, 'F - test_inserting_text_on_final_line_avoids_scrolling_down_when_not_at_bottom/screen_top')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_inserting_text_on_final_line_avoids_scrolling_down_when_not_at_bottom/cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'F - test_inserting_text_on_final_line_avoids_scrolling_down_when_not_at_bottom/cursor:pos')
  local y = Editor_state.top
  App.screen.check(y, 'a', 'F - test_inserting_text_on_final_line_avoids_scrolling_down_when_not_at_bottom/screen:1')
end
function test_typing_on_bottom_line_scrolls_down()
  io.write('\ntest_typing_on_bottom_line_scrolls_down')
  -- display a few lines with cursor on bottom line
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=3, pos=4}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_typing_on_bottom_line_scrolls_down/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_typing_on_bottom_line_scrolls_down/baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'F - test_typing_on_bottom_line_scrolls_down/baseline/screen:3')
  -- after typing something the line wraps and the screen scrolls down
  edit.run_after_textinput(Editor_state, 'j')
  edit.run_after_textinput(Editor_state, 'k')
  edit.run_after_textinput(Editor_state, 'l')
  check_eq(Editor_state.screen_top1.line, 2, 'F - test_typing_on_bottom_line_scrolls_down/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'F - test_typing_on_bottom_line_scrolls_down/cursor:line')
  check_eq(Editor_state.cursor1.pos, 7, 'F - test_typing_on_bottom_line_scrolls_down/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'def', 'F - test_typing_on_bottom_line_scrolls_down/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghij', 'F - test_typing_on_bottom_line_scrolls_down/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'kl', 'F - test_typing_on_bottom_line_scrolls_down/screen:3')
end
function test_left_arrow_scrolls_up_in_wrapped_line()
  io.write('\ntest_left_arrow_scrolls_up_in_wrapped_line')
  -- display lines starting from second screen line of a line
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi jkl', 'mno'}
  Text.redraw_all(Editor_state)
  Editor_state.screen_top1 = {line=3, pos=5}
  Editor_state.screen_bottom1 = {}
  -- cursor is at top of screen
  Editor_state.cursor1 = {line=3, pos=5}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'jkl', 'F - test_left_arrow_scrolls_up_in_wrapped_line/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno', 'F - test_left_arrow_scrolls_up_in_wrapped_line/baseline/screen:2')
  -- after hitting the left arrow the screen scrolls up to first screen line
  edit.run_after_keychord(Editor_state, 'left')
  y = Editor_state.top
  App.screen.check(y, 'ghi ', 'F - test_left_arrow_scrolls_up_in_wrapped_line/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'F - test_left_arrow_scrolls_up_in_wrapped_line/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno', 'F - test_left_arrow_scrolls_up_in_wrapped_line/screen:3')
  check_eq(Editor_state.screen_top1.line, 3, 'F - test_left_arrow_scrolls_up_in_wrapped_line/screen_top')
  check_eq(Editor_state.screen_top1.pos, 1, 'F - test_left_arrow_scrolls_up_in_wrapped_line/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'F - test_left_arrow_scrolls_up_in_wrapped_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 4, 'F - test_left_arrow_scrolls_up_in_wrapped_line/cursor:pos')
end
function test_right_arrow_scrolls_down_in_wrapped_line()
  io.write('\ntest_right_arrow_scrolls_down_in_wrapped_line')
  -- display the first three lines with the cursor on the bottom line
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi jkl', 'mno'}
  Text.redraw_all(Editor_state)
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  -- cursor is at bottom right of screen
  Editor_state.cursor1 = {line=3, pos=5}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_right_arrow_scrolls_down_in_wrapped_line/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_right_arrow_scrolls_down_in_wrapped_line/baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi ', 'F - test_right_arrow_scrolls_down_in_wrapped_line/baseline/screen:3')  -- line wrapping includes trailing whitespace
  -- after hitting the right arrow the screen scrolls down by one line
  edit.run_after_keychord(Editor_state, 'right')
  check_eq(Editor_state.screen_top1.line, 2, 'F - test_right_arrow_scrolls_down_in_wrapped_line/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'F - test_right_arrow_scrolls_down_in_wrapped_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 6, 'F - test_right_arrow_scrolls_down_in_wrapped_line/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'def', 'F - test_right_arrow_scrolls_down_in_wrapped_line/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi ', 'F - test_right_arrow_scrolls_down_in_wrapped_line/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'F - test_right_arrow_scrolls_down_in_wrapped_line/screen:3')
end
function test_home_scrolls_up_in_wrapped_line()
  io.write('\ntest_home_scrolls_up_in_wrapped_line')
  -- display lines starting from second screen line of a line
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi jkl', 'mno'}
  Text.redraw_all(Editor_state)
  Editor_state.screen_top1 = {line=3, pos=5}
  Editor_state.screen_bottom1 = {}
  -- cursor is at top of screen
  Editor_state.cursor1 = {line=3, pos=5}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'jkl', 'F - test_home_scrolls_up_in_wrapped_line/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno', 'F - test_home_scrolls_up_in_wrapped_line/baseline/screen:2')
  -- after hitting home the screen scrolls up to first screen line
  edit.run_after_keychord(Editor_state, 'home')
  y = Editor_state.top
  App.screen.check(y, 'ghi ', 'F - test_home_scrolls_up_in_wrapped_line/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'F - test_home_scrolls_up_in_wrapped_line/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno', 'F - test_home_scrolls_up_in_wrapped_line/screen:3')
  check_eq(Editor_state.screen_top1.line, 3, 'F - test_home_scrolls_up_in_wrapped_line/screen_top')
  check_eq(Editor_state.screen_top1.pos, 1, 'F - test_home_scrolls_up_in_wrapped_line/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'F - test_home_scrolls_up_in_wrapped_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_home_scrolls_up_in_wrapped_line/cursor:pos')
end
function test_end_scrolls_down_in_wrapped_line()
  io.write('\ntest_end_scrolls_down_in_wrapped_line')
  -- display the first three lines with the cursor on the bottom line
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi jkl', 'mno'}
  Text.redraw_all(Editor_state)
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  -- cursor is at bottom right of screen
  Editor_state.cursor1 = {line=3, pos=5}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_end_scrolls_down_in_wrapped_line/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_end_scrolls_down_in_wrapped_line/baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi ', 'F - test_end_scrolls_down_in_wrapped_line/baseline/screen:3')  -- line wrapping includes trailing whitespace
  -- after hitting end the screen scrolls down by one line
  edit.run_after_keychord(Editor_state, 'end')
  check_eq(Editor_state.screen_top1.line, 2, 'F - test_end_scrolls_down_in_wrapped_line/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'F - test_end_scrolls_down_in_wrapped_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 8, 'F - test_end_scrolls_down_in_wrapped_line/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'def', 'F - test_end_scrolls_down_in_wrapped_line/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi ', 'F - test_end_scrolls_down_in_wrapped_line/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'F - test_end_scrolls_down_in_wrapped_line/screen:3')
end
function test_position_cursor_on_recently_edited_wrapping_line()
  -- draw a line wrapping over 2 screen lines
  io.write('\ntest_position_cursor_on_recently_edited_wrapping_line')
  App.screen.init{width=100, height=200}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def ghi jkl mno pqr ', 'xyz'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=25}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'abc def ghi ', 'F - test_position_cursor_on_recently_edited_wrapping_line/baseline1/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl mno pqr ', 'F - test_position_cursor_on_recently_edited_wrapping_line/baseline1/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'xyz', 'F - test_position_cursor_on_recently_edited_wrapping_line/baseline1/screen:3')
  -- add to the line until it's wrapping over 3 screen lines
  edit.run_after_textinput(Editor_state, 's')
  edit.run_after_textinput(Editor_state, 't')
  edit.run_after_textinput(Editor_state, 'u')
  check_eq(Editor_state.cursor1.pos, 28, 'F - test_position_cursor_on_recently_edited_wrapping_line/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'abc def ghi ', 'F - test_position_cursor_on_recently_edited_wrapping_line/baseline2/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl mno pqr ', 'F - test_position_cursor_on_recently_edited_wrapping_line/baseline2/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'stu', 'F - test_position_cursor_on_recently_edited_wrapping_line/baseline2/screen:3')
  -- try to move the cursor earlier in the third screen line by clicking the mouse
  edit.run_after_mouse_press(Editor_state, Editor_state.left+8,Editor_state.top+Editor_state.line_height*2+5, 1)
  -- cursor should move
  check_eq(Editor_state.cursor1.line, 1, 'F - test_position_cursor_on_recently_edited_wrapping_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 26, 'F - test_position_cursor_on_recently_edited_wrapping_line/cursor:pos')
end
function test_backspace_can_scroll_up()
  io.write('\ntest_backspace_can_scroll_up')
  -- display the lines 2/3/4 with the cursor on line 2
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=2, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'def', 'F - test_backspace_can_scroll_up/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'F - test_backspace_can_scroll_up/baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'F - test_backspace_can_scroll_up/baseline/screen:3')
  -- after hitting backspace the screen scrolls up by one line
  edit.run_after_keychord(Editor_state, 'backspace')
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_backspace_can_scroll_up/screen_top')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_backspace_can_scroll_up/cursor')
  y = Editor_state.top
  App.screen.check(y, 'abcdef', 'F - test_backspace_can_scroll_up/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'F - test_backspace_can_scroll_up/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'F - test_backspace_can_scroll_up/screen:3')
end
function test_backspace_can_scroll_up_screen_line()
  io.write('\ntest_backspace_can_scroll_up_screen_line')
  -- display lines starting from second screen line of a line
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi jkl', 'mno'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=3, pos=5}
  Editor_state.screen_top1 = {line=3, pos=5}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'jkl', 'F - test_backspace_can_scroll_up_screen_line/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno', 'F - test_backspace_can_scroll_up_screen_line/baseline/screen:2')
  -- after hitting backspace the screen scrolls up by one screen line
  edit.run_after_keychord(Editor_state, 'backspace')
  y = Editor_state.top
  App.screen.check(y, 'ghij', 'F - test_backspace_can_scroll_up_screen_line/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'kl', 'F - test_backspace_can_scroll_up_screen_line/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno', 'F - test_backspace_can_scroll_up_screen_line/screen:3')
  check_eq(Editor_state.screen_top1.line, 3, 'F - test_backspace_can_scroll_up_screen_line/screen_top')
  check_eq(Editor_state.screen_top1.pos, 1, 'F - test_backspace_can_scroll_up_screen_line/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'F - test_backspace_can_scroll_up_screen_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 4, 'F - test_backspace_can_scroll_up_screen_line/cursor:pos')
end
function test_backspace_past_line_boundary()
  io.write('\ntest_backspace_past_line_boundary')
  -- position cursor at start of a (non-first) line
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  -- backspace joins with previous line
  edit.run_after_keychord(Editor_state, 'backspace')
  check_eq(Editor_state.lines[1].data, 'abcdef', "F - test_backspace_past_line_boundary")
end
function test_undo_insert_text()
  io.write('\ntest_undo_insert_text')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'xyz'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=4}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  -- insert a character
  edit.draw(Editor_state)
  edit.run_after_textinput(Editor_state, 'g')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_undo_insert_text/baseline/cursor:line')
  check_eq(Editor_state.cursor1.pos, 5, 'F - test_undo_insert_text/baseline/cursor:pos')
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_undo_insert_text/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'defg', 'F - test_undo_insert_text/baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'xyz', 'F - test_undo_insert_text/baseline/screen:3')
  -- undo
  edit.run_after_keychord(Editor_state, 'C-z')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_undo_insert_text/cursor:line')
  check_eq(Editor_state.cursor1.pos, 4, 'F - test_undo_insert_text/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_undo_insert_text/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_undo_insert_text/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'xyz', 'F - test_undo_insert_text/screen:3')
end
function test_undo_delete_text()
  io.write('\ntest_undo_delete_text')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'defg', 'xyz'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=5}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  -- delete a character
  edit.run_after_keychord(Editor_state, 'backspace')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_undo_delete_text/baseline/cursor:line')
  check_eq(Editor_state.cursor1.pos, 4, 'F - test_undo_delete_text/baseline/cursor:pos')
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_undo_delete_text/baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'F - test_undo_delete_text/baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'xyz', 'F - test_undo_delete_text/baseline/screen:3')
  -- undo
--?   -- after undo, the backspaced key is selected
  edit.run_after_keychord(Editor_state, 'C-z')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_undo_delete_text/cursor:line')
  check_eq(Editor_state.cursor1.pos, 5, 'F - test_undo_delete_text/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_undo_delete_text/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'defg', 'F - test_undo_delete_text/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'xyz', 'F - test_undo_delete_text/screen:3')
end
function test_search()
  io.write('\ntest_search')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'deg'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  -- search for a string
  edit.run_after_keychord(Editor_state, 'C-f')
  edit.run_after_textinput(Editor_state, 'd')
  edit.run_after_keychord(Editor_state, 'return')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_search/1/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_search/1/cursor:pos')
  -- reset cursor
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  -- search for second occurrence
  edit.run_after_keychord(Editor_state, 'C-f')
  edit.run_after_textinput(Editor_state, 'de')
  edit.run_after_keychord(Editor_state, 'down')
  edit.run_after_keychord(Editor_state, 'return')
  check_eq(Editor_state.cursor1.line, 4, 'F - test_search/2/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_search/2/cursor:pos')
end
function test_search_upwards()
  io.write('\ntest_search_upwards')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc abd'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=2}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  -- search for a string
  edit.run_after_keychord(Editor_state, 'C-f')
  edit.run_after_textinput(Editor_state, 'a')
  -- search for previous occurrence
  edit.run_after_keychord(Editor_state, 'up')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_search_upwards/2/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_search_upwards/2/cursor:pos')
end
function test_search_wrap()
  io.write('\ntest_search_wrap')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=3}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  -- search for a string
  edit.run_after_keychord(Editor_state, 'C-f')
  edit.run_after_textinput(Editor_state, 'a')
  edit.run_after_keychord(Editor_state, 'return')
  -- cursor wraps
  check_eq(Editor_state.cursor1.line, 1, 'F - test_search_wrap/1/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_search_wrap/1/cursor:pos')
end
function test_search_wrap_upwards()
  io.write('\ntest_search_wrap_upwards')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc abd'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  -- search upwards for a string
  edit.run_after_keychord(Editor_state, 'C-f')
  edit.run_after_textinput(Editor_state, 'a')
  edit.run_after_keychord(Editor_state, 'up')
  -- cursor wraps
  check_eq(Editor_state.cursor1.line, 1, 'F - test_search_wrap_upwards/1/cursor:line')
  check_eq(Editor_state.cursor1.pos, 5, 'F - test_search_wrap_upwards/1/cursor:pos')
end

-- text editor, particularly text drawing, horizontal wrap, vertical scrolling
Text = {}
AB_padding = 20  -- space in pixels between A side and B side
-- draw a line starting from startpos to screen at y between State.left and State.right
-- return the final y, and pos,posB of start of final screen line drawn
function Text.draw(State, line_index, y, startpos, startposB)
  local line = State.lines[line_index]
  local line_cache = State.line_cache[line_index]
  line_cache.starty = y
  line_cache.startpos = startpos
  line_cache.startposB = startposB
  -- draw A side
  local overflows_screen, x, pos, screen_line_starting_pos
  if startpos then
    overflows_screen, x, y, pos, screen_line_starting_pos = Text.draw_wrapping_line(State, line_index, State.left, y, startpos)
    if overflows_screen then
      return y, screen_line_starting_pos
    end
    if Focus == 'edit' and State.cursor1.pos then
      if State.search_term == nil then
        if line_index == State.cursor1.line and State.cursor1.pos == pos then
          Text.draw_cursor(State, x, y)
        end
      end
    end
  else
    x = State.left
  end
  -- check for B side
--?   if line_index == 8 then print('checking for B side') end
  if line.dataB == nil then
    assert(y)
    assert(screen_line_starting_pos)
--?     if line_index == 8 then print('return 1') end
    return y, screen_line_starting_pos
  end
  if not State.expanded and not line.expanded then
    assert(y)
    assert(screen_line_starting_pos)
--?     if line_index == 8 then print('return 2') end
    button(State, 'expand', {x=x+AB_padding, y=y+2, w=App.width(State.em), h=State.line_height-4, color={1,1,1},
      icon = function(button_params)
               App.color(Fold_background_color)
               love.graphics.rectangle('fill', button_params.x, button_params.y, App.width(State.em), State.line_height-4, 2,2)
             end,
      onpress1 = function()
                   line.expanded = true
                 end,
    })
    return y, screen_line_starting_pos
  end
  -- draw B side
--?   if line_index == 8 then print('drawing B side') end
  App.color(Fold_color)
--?   if Foo then
--?     print('draw:', State.lines[line_index].data, "=====", State.lines[line_index].dataB, 'starting from x', x+AB_padding)
--?   end
  if startposB then
    overflows_screen, x, y, pos, screen_line_starting_pos = Text.draw_wrapping_lineB(State, line_index, x,y, startposB)
  else
    overflows_screen, x, y, pos, screen_line_starting_pos = Text.draw_wrapping_lineB(State, line_index, x+AB_padding,y, 1)
  end
  if overflows_screen then
    return y, nil, screen_line_starting_pos
  end
--?   if line_index == 8 then print('a') end
  if Focus == 'edit' and State.cursor1.posB then
--?     if line_index == 8 then print('b') end
    if State.search_term == nil then
--?       if line_index == 8 then print('c', State.cursor1.line, State.cursor1.posB, line_index, pos) end
      if line_index == State.cursor1.line and State.cursor1.posB == pos then
        Text.draw_cursor(State, x, y)
      end
    end
  end
  return y, nil, screen_line_starting_pos
end
-- Given an array of fragments, draw the subset starting from pos to screen
-- starting from (x,y).
-- Return:
--  - whether we got to bottom of screen before end of line
--  - the final (x,y)
--  - the final pos
--  - starting pos of the final screen line drawn
function Text.draw_wrapping_line(State, line_index, x,y, startpos)
  local line = State.lines[line_index]
  local line_cache = State.line_cache[line_index]
--?   print('== line', line_index, '^'..line.data..'$')
  local screen_line_starting_pos = startpos
  Text.compute_fragments(State, line_index)
  local pos = 1
  initialize_color()
  for _, f in ipairs(line_cache.fragments) do
    App.color(Text_color)
    local frag, frag_text = f.data, f.text
    select_color(frag)
    local frag_len = utf8.len(frag)
--?     print('text.draw:', frag, 'at', line_index,pos, 'after', x,y)
    if pos < startpos then
      -- render nothing
--?       print('skipping', frag)
    else
      -- render fragment
      local frag_width = App.width(frag_text)
      if x + frag_width > State.right then
        assert(x > State.left)  -- no overfull lines
        y = y + State.line_height
        if y + State.line_height > App.screen.height then
          return --[[screen filled]] true, x,y, pos, screen_line_starting_pos
        end
        screen_line_starting_pos = pos
        x = State.left
      end
      App.screen.draw(frag_text, x,y)
      -- render cursor if necessary
      if State.cursor1.pos and line_index == State.cursor1.line then
        if pos <= State.cursor1.pos and pos + frag_len > State.cursor1.pos then
          if State.search_term then
            if State.lines[State.cursor1.line].data:sub(State.cursor1.pos, State.cursor1.pos+utf8.len(State.search_term)-1) == State.search_term then
              local lo_px = Text.draw_highlight(State, line, x,y, pos, State.cursor1.pos, State.cursor1.pos+utf8.len(State.search_term))
              App.color(Text_color)
              love.graphics.print(State.search_term, x+lo_px,y)
            end
          elseif Focus == 'edit' then
            Text.draw_cursor(State, x+Text.x(frag, State.cursor1.pos-pos+1), y)
            App.color(Text_color)
          end
        end
      end
      x = x + frag_width
    end
    pos = pos + frag_len
  end
  return false, x,y, pos, screen_line_starting_pos
end
function Text.draw_wrapping_lineB(State, line_index, x,y, startpos)
  local line = State.lines[line_index]
  local line_cache = State.line_cache[line_index]
  local screen_line_starting_pos = startpos
  Text.compute_fragmentsB(State, line_index, x)
  local pos = 1
  for _, f in ipairs(line_cache.fragmentsB) do
    local frag, frag_text = f.data, f.text
    local frag_len = utf8.len(frag)
--?     print('text.draw:', frag, 'at', line_index,pos, 'after', x,y)
    if pos < startpos then
      -- render nothing
--?       print('skipping', frag)
    else
      -- render fragment
      local frag_width = App.width(frag_text)
      if x + frag_width > State.right then
        assert(x > State.left)  -- no overfull lines
        y = y + State.line_height
        if y + State.line_height > App.screen.height then
          return --[[screen filled]] true, x,y, pos, screen_line_starting_pos
        end
        screen_line_starting_pos = pos
        x = State.left
      end
      App.screen.draw(frag_text, x,y)
      -- render cursor if necessary
      if State.cursor1.posB and line_index == State.cursor1.line then
        if pos <= State.cursor1.posB and pos + frag_len > State.cursor1.posB then
          if State.search_term then
            if State.lines[State.cursor1.line].dataB:sub(State.cursor1.posB, State.cursor1.posB+utf8.len(State.search_term)-1) == State.search_term then
              local lo_px = Text.draw_highlight(State, line, x,y, pos, State.cursor1.posB, State.cursor1.posB+utf8.len(State.search_term))
              App.color(Fold_color)
              love.graphics.print(State.search_term, x+lo_px,y)
            end
          elseif Focus == 'edit' then
            Text.draw_cursor(State, x+Text.x(frag, State.cursor1.posB-pos+1), y)
            App.color(Fold_color)
          end
        end
      end
      x = x + frag_width
    end
    pos = pos + frag_len
  end
  return false, x,y, pos, screen_line_starting_pos
end
function Text.draw_cursor(State, x, y)
  -- blink every 0.5s
  if math.floor(Cursor_time*2)%2 == 0 then
    App.color(Cursor_color)
    love.graphics.rectangle('fill', x,y, 3,State.line_height)
  end
  State.cursor_x = x
  State.cursor_y = y+State.line_height
end
function Text.populate_screen_line_starting_pos(State, line_index)
  local line = State.lines[line_index]
  local line_cache = State.line_cache[line_index]
  if line_cache.screen_line_starting_pos then
    return
  end
  -- duplicate some logic from Text.draw
  Text.compute_fragments(State, line_index)
  line_cache.screen_line_starting_pos = {1}
  local x = State.left
  local pos = 1
  for _, f in ipairs(line_cache.fragments) do
    local frag, frag_text = f.data, f.text
    -- render fragment
    local frag_width = App.width(frag_text)
    if x + frag_width > State.right then
      x = State.left
      table.insert(line_cache.screen_line_starting_pos, pos)
    end
    x = x + frag_width
    local frag_len = utf8.len(frag)
    pos = pos + frag_len
  end
end
function Text.compute_fragments(State, line_index)
--?   print('compute_fragments', line_index, 'between', State.left, State.right)
  local line = State.lines[line_index]
  local line_cache = State.line_cache[line_index]
  if line_cache.fragments then
    return
  end
  line_cache.fragments = {}
  local x = State.left
  -- try to wrap at word boundaries
  for frag in line.data:gmatch('%S*%s*') do
    local frag_text = App.newText(love.graphics.getFont(), frag)
    local frag_width = App.width(frag_text)
--?     print('x: '..tostring(x)..'; frag_width: '..tostring(frag_width)..'; '..tostring(State.right-x)..'px to go')
    while x + frag_width > State.right do
--?       print(('checking whether to split fragment ^%s$ of width %d when rendering from %d'):format(frag, frag_width, x))
      if (x-State.left) < 0.8 * (State.right-State.left) then
--?         print('splitting')
        -- long word; chop it at some letter
        -- We're not going to reimplement TeX here.
        local bpos = Text.nearest_pos_less_than(frag, State.right - x)
--?         print('bpos', bpos)
        if bpos == 0 then break end  -- avoid infinite loop when window is too narrow
        local boffset = Text.offset(frag, bpos+1)  -- byte _after_ bpos
--?         print('space for '..tostring(bpos)..' graphemes, '..tostring(boffset-1)..' bytes')
        local frag1 = string.sub(frag, 1, boffset-1)
        local frag1_text = App.newText(love.graphics.getFont(), frag1)
        local frag1_width = App.width(frag1_text)
--?         print('extracting ^'..frag1..'$ of width '..tostring(frag1_width)..'px')
        assert(x + frag1_width <= State.right)
        table.insert(line_cache.fragments, {data=frag1, text=frag1_text})
        frag = string.sub(frag, boffset)
        frag_text = App.newText(love.graphics.getFont(), frag)
        frag_width = App.width(frag_text)
      end
      x = State.left  -- new line
    end
    if #frag > 0 then
--?       print('inserting ^'..frag..'$ of width '..tostring(frag_width)..'px')
      table.insert(line_cache.fragments, {data=frag, text=frag_text})
    end
    x = x + frag_width
  end
end
function Text.populate_screen_line_starting_posB(State, line_index, x)
  local line = State.lines[line_index]
  local line_cache = State.line_cache[line_index]
  if line_cache.screen_line_starting_posB then
    return
  end
  -- duplicate some logic from Text.draw
  Text.compute_fragmentsB(State, line_index, x)
  line_cache.screen_line_starting_posB = {1}
  local pos = 1
  for _, f in ipairs(line_cache.fragmentsB) do
    local frag, frag_text = f.data, f.text
    -- render fragment
    local frag_width = App.width(frag_text)
    if x + frag_width > State.right then
      x = State.left
      table.insert(line_cache.screen_line_starting_posB, pos)
    end
    x = x + frag_width
    local frag_len = utf8.len(frag)
    pos = pos + frag_len
  end
end
function Text.compute_fragmentsB(State, line_index, x)
--?   print('compute_fragmentsB', line_index, 'between', x, State.right)
  local line = State.lines[line_index]
  local line_cache = State.line_cache[line_index]
  if line_cache.fragmentsB then
    return
  end
  line_cache.fragmentsB = {}
  -- try to wrap at word boundaries
  for frag in line.dataB:gmatch('%S*%s*') do
    local frag_text = App.newText(love.graphics.getFont(), frag)
    local frag_width = App.width(frag_text)
--?     print('x: '..tostring(x)..'; '..tostring(State.right-x)..'px to go')
    while x + frag_width > State.right do
--?       print(('checking whether to split fragment ^%s$ of width %d when rendering from %d'):format(frag, frag_width, x))
      if (x-State.left) < 0.8 * (State.right-State.left) then
--?         print('splitting')
        -- long word; chop it at some letter
        -- We're not going to reimplement TeX here.
        local bpos = Text.nearest_pos_less_than(frag, State.right - x)
--?         print('bpos', bpos)
        if bpos == 0 then break end  -- avoid infinite loop when window is too narrow
        local boffset = Text.offset(frag, bpos+1)  -- byte _after_ bpos
--?         print('space for '..tostring(bpos)..' graphemes, '..tostring(boffset-1)..' bytes')
        local frag1 = string.sub(frag, 1, boffset-1)
        local frag1_text = App.newText(love.graphics.getFont(), frag1)
        local frag1_width = App.width(frag1_text)
--?         print('extracting ^'..frag1..'$ of width '..tostring(frag1_width)..'px')
        assert(x + frag1_width <= State.right)
        table.insert(line_cache.fragmentsB, {data=frag1, text=frag1_text})
        frag = string.sub(frag, boffset)
        frag_text = App.newText(love.graphics.getFont(), frag)
        frag_width = App.width(frag_text)
      end
      x = State.left  -- new line
    end
    if #frag > 0 then
--?       print('inserting ^'..frag..'$ of width '..tostring(frag_width)..'px')
      table.insert(line_cache.fragmentsB, {data=frag, text=frag_text})
    end
    x = x + frag_width
  end
end
function Text.textinput(State, t)
  if App.mouse_down(1) then return end
  if App.ctrl_down() or App.alt_down() or App.cmd_down() then return end
  local before = snapshot(State, State.cursor1.line)
--?   print(State.screen_top1.line, State.screen_top1.pos, State.cursor1.line, State.cursor1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)
  Text.insert_at_cursor(State, t)
  if State.cursor_y > App.screen.height - State.line_height then
    Text.populate_screen_line_starting_pos(State, State.cursor1.line)
    Text.snap_cursor_to_bottom_of_screen(State, State.left, State.right)
  end
  record_undo_event(State, {before=before, after=snapshot(State, State.cursor1.line)})
end
function Text.insert_at_cursor(State, t)
  if State.cursor1.pos then
    local byte_offset = Text.offset(State.lines[State.cursor1.line].data, State.cursor1.pos)
    State.lines[State.cursor1.line].data = string.sub(State.lines[State.cursor1.line].data, 1, byte_offset-1)..t..string.sub(State.lines[State.cursor1.line].data, byte_offset)
    Text.clear_screen_line_cache(State, State.cursor1.line)
    State.cursor1.pos = State.cursor1.pos+1
  else
    assert(State.cursor1.posB)
    local byte_offset = Text.offset(State.lines[State.cursor1.line].dataB, State.cursor1.posB)
    State.lines[State.cursor1.line].dataB = string.sub(State.lines[State.cursor1.line].dataB, 1, byte_offset-1)..t..string.sub(State.lines[State.cursor1.line].dataB, byte_offset)
    Text.clear_screen_line_cache(State, State.cursor1.line)
    State.cursor1.posB = State.cursor1.posB+1
  end
end
-- Don't handle any keys here that would trigger love.textinput above.
function Text.keychord_pressed(State, chord)
--?   print('chord', chord)
  --== shortcuts that mutate text
  if chord == 'return' then
    local before_line = State.cursor1.line
    local before = snapshot(State, before_line)
    Text.insert_return(State)
    if State.cursor_y > App.screen.height - State.line_height then
      Text.snap_cursor_to_bottom_of_screen(State, State.left, State.right)
    end
    schedule_save(State)
    record_undo_event(State, {before=before, after=snapshot(State, before_line, State.cursor1.line)})
  elseif chord == 'tab' then
    local before = snapshot(State, State.cursor1.line)
--?     print(State.screen_top1.line, State.screen_top1.pos, State.cursor1.line, State.cursor1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)
    Text.insert_at_cursor(State, '\t')
    if State.cursor_y > App.screen.height - State.line_height then
      Text.populate_screen_line_starting_pos(State, State.cursor1.line)
      Text.snap_cursor_to_bottom_of_screen(State, State.left, State.right)
--?       print('=>', State.screen_top1.line, State.screen_top1.pos, State.cursor1.line, State.cursor1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)
    end
    schedule_save(State)
    record_undo_event(State, {before=before, after=snapshot(State, State.cursor1.line)})
  elseif chord == 'backspace' then
    local before
    if State.cursor1.pos and State.cursor1.pos > 1 then
      before = snapshot(State, State.cursor1.line)
      local byte_start = utf8.offset(State.lines[State.cursor1.line].data, State.cursor1.pos-1)
      local byte_end = utf8.offset(State.lines[State.cursor1.line].data, State.cursor1.pos)
      if byte_start then
        if byte_end then
          State.lines[State.cursor1.line].data = string.sub(State.lines[State.cursor1.line].data, 1, byte_start-1)..string.sub(State.lines[State.cursor1.line].data, byte_end)
        else
          State.lines[State.cursor1.line].data = string.sub(State.lines[State.cursor1.line].data, 1, byte_start-1)
        end
        State.cursor1.pos = State.cursor1.pos-1
      end
    elseif State.cursor1.posB then
      if State.cursor1.posB > 1 then
        before = snapshot(State, State.cursor1.line)
        local byte_start = utf8.offset(State.lines[State.cursor1.line].dataB, State.cursor1.posB-1)
        local byte_end = utf8.offset(State.lines[State.cursor1.line].dataB, State.cursor1.posB)
        if byte_start then
          if byte_end then
            State.lines[State.cursor1.line].dataB = string.sub(State.lines[State.cursor1.line].dataB, 1, byte_start-1)..string.sub(State.lines[State.cursor1.line].dataB, byte_end)
          else
            State.lines[State.cursor1.line].dataB = string.sub(State.lines[State.cursor1.line].dataB, 1, byte_start-1)
          end
          State.cursor1.posB = State.cursor1.posB-1
        end
      else
        -- refuse to delete past beginning of side B
      end
    elseif State.cursor1.line > 1 then
      before = snapshot(State, State.cursor1.line-1, State.cursor1.line)
      -- join lines
      State.cursor1.pos = utf8.len(State.lines[State.cursor1.line-1].data)+1
      State.lines[State.cursor1.line-1].data = State.lines[State.cursor1.line-1].data..State.lines[State.cursor1.line].data
      table.remove(State.lines, State.cursor1.line)
      table.remove(State.line_cache, State.cursor1.line)
      State.cursor1.line = State.cursor1.line-1
    end
    if State.screen_top1.line > #State.lines then
      Text.populate_screen_line_starting_pos(State, #State.lines)
      local line_cache = State.line_cache[#State.line_cache]
      State.screen_top1 = {line=#State.lines, pos=line_cache.screen_line_starting_pos[#line_cache.screen_line_starting_pos]}
    elseif Text.lt1(State.cursor1, State.screen_top1) then
      local top2 = Text.to2(State, State.screen_top1)
      top2 = Text.previous_screen_line(State, top2, State.left, State.right)
      State.screen_top1 = Text.to1(State, top2)
      Text.redraw_all(State)  -- if we're scrolling, reclaim all fragments to avoid memory leaks
    end
    Text.clear_screen_line_cache(State, State.cursor1.line)
    assert(Text.le1(State.screen_top1, State.cursor1))
    schedule_save(State)
    record_undo_event(State, {before=before, after=snapshot(State, State.cursor1.line)})
  elseif chord == 'delete' then
    local before
    if State.cursor1.posB or State.cursor1.pos <= utf8.len(State.lines[State.cursor1.line].data) then
      before = snapshot(State, State.cursor1.line)
    else
      before = snapshot(State, State.cursor1.line, State.cursor1.line+1)
    end
    if State.cursor1.pos and State.cursor1.pos <= utf8.len(State.lines[State.cursor1.line].data) then
      local byte_start = utf8.offset(State.lines[State.cursor1.line].data, State.cursor1.pos)
      local byte_end = utf8.offset(State.lines[State.cursor1.line].data, State.cursor1.pos+1)
      if byte_start then
        if byte_end then
          State.lines[State.cursor1.line].data = string.sub(State.lines[State.cursor1.line].data, 1, byte_start-1)..string.sub(State.lines[State.cursor1.line].data, byte_end)
        else
          State.lines[State.cursor1.line].data = string.sub(State.lines[State.cursor1.line].data, 1, byte_start-1)
        end
        -- no change to State.cursor1.pos
      end
    elseif State.cursor1.posB then
      if State.cursor1.posB <= utf8.len(State.lines[State.cursor1.line].dataB) then
        local byte_start = utf8.offset(State.lines[State.cursor1.line].dataB, State.cursor1.posB)
        local byte_end = utf8.offset(State.lines[State.cursor1.line].dataB, State.cursor1.posB+1)
        if byte_start then
          if byte_end then
            State.lines[State.cursor1.line].dataB = string.sub(State.lines[State.cursor1.line].dataB, 1, byte_start-1)..string.sub(State.lines[State.cursor1.line].dataB, byte_end)
          else
            State.lines[State.cursor1.line].dataB = string.sub(State.lines[State.cursor1.line].dataB, 1, byte_start-1)
          end
          -- no change to State.cursor1.pos
        end
      else
        -- refuse to delete past end of side B
      end
    elseif State.cursor1.line < #State.lines then
      -- join lines
      State.lines[State.cursor1.line].data = State.lines[State.cursor1.line].data..State.lines[State.cursor1.line+1].data
      -- delete side B on first line
      State.lines[State.cursor1.line].dataB = State.lines[State.cursor1.line+1].dataB
      table.remove(State.lines, State.cursor1.line+1)
      table.remove(State.line_cache, State.cursor1.line+1)
    end
    Text.clear_screen_line_cache(State, State.cursor1.line)
    schedule_save(State)
    record_undo_event(State, {before=before, after=snapshot(State, State.cursor1.line)})
  --== shortcuts that move the cursor
  elseif chord == 'left' then
    Text.left(State)
  elseif chord == 'right' then
    Text.right(State)
  elseif chord == 'S-left' then
    Text.left(State)
  elseif chord == 'S-right' then
    Text.right(State)
  -- C- hotkeys reserved for drawings, so we'll use M-
  elseif chord == 'M-left' then
    Text.word_left(State)
  elseif chord == 'M-right' then
    Text.word_right(State)
  elseif chord == 'M-S-left' then
    Text.word_left(State)
  elseif chord == 'M-S-right' then
    Text.word_right(State)
  elseif chord == 'home' then
    Text.start_of_line(State)
  elseif chord == 'end' then
    Text.end_of_line(State)
  elseif chord == 'S-home' then
    Text.start_of_line(State)
  elseif chord == 'S-end' then
    Text.end_of_line(State)
  elseif chord == 'up' then
    Text.up(State)
  elseif chord == 'down' then
    Text.down(State)
  elseif chord == 'S-up' then
    Text.up(State)
  elseif chord == 'S-down' then
    Text.down(State)
  elseif chord == 'pageup' then
    Text.pageup(State)
  elseif chord == 'pagedown' then
    Text.pagedown(State)
  elseif chord == 'S-pageup' then
    Text.pageup(State)
  elseif chord == 'S-pagedown' then
    Text.pagedown(State)
  end
end
function Text.insert_return(State)
  if State.cursor1.pos then
    -- when inserting a newline, move any B side to the new line
    local byte_offset = Text.offset(State.lines[State.cursor1.line].data, State.cursor1.pos)
    table.insert(State.lines, State.cursor1.line+1, {data=string.sub(State.lines[State.cursor1.line].data, byte_offset), dataB=State.lines[State.cursor1.line].dataB})
    table.insert(State.line_cache, State.cursor1.line+1, {})
    State.lines[State.cursor1.line].data = string.sub(State.lines[State.cursor1.line].data, 1, byte_offset-1)
    State.lines[State.cursor1.line].dataB = nil
    Text.clear_screen_line_cache(State, State.cursor1.line)
    State.cursor1 = {line=State.cursor1.line+1, pos=1}
  else
    -- disable enter when cursor is on the B side
  end
end
function Text.pageup(State)
--?   print('pageup')
  -- duplicate some logic from love.draw
  local top2 = Text.to2(State, State.screen_top1)
--?   print(App.screen.height)
  local y = App.screen.height - State.line_height
  while y >= State.top do
--?     print(y, top2.line, top2.screen_line, top2.screen_pos)
    if State.screen_top1.line == 1 and State.screen_top1.pos and State.screen_top1.pos == 1 then break end
    y = y - State.line_height
    top2 = Text.previous_screen_line(State, top2)
  end
  State.screen_top1 = Text.to1(State, top2)
  State.cursor1 = {line=State.screen_top1.line, pos=State.screen_top1.pos, posB=State.screen_top1.posB}
  Text.move_cursor_down_to_next_text_line_while_scrolling_again_if_necessary(State)
--?   print(State.cursor1.line, State.cursor1.pos, State.screen_top1.line, State.screen_top1.pos)
--?   print('pageup end')
end
function Text.pagedown(State)
--?   print('pagedown')
  local bot2 = Text.to2(State, State.screen_bottom1)
  local new_top1 = Text.to1(State, bot2)
  if Text.lt1(State.screen_top1, new_top1) then
    State.screen_top1 = new_top1
  else
    State.screen_top1 = {line=State.screen_bottom1.line, pos=State.screen_bottom1.pos}
  end
--?   print('setting top to', State.screen_top1.line, State.screen_top1.pos)
  State.cursor1 = {line=State.screen_top1.line, pos=State.screen_top1.pos, posB=State.screen_top1.posB}
  Text.move_cursor_down_to_next_text_line_while_scrolling_again_if_necessary(State)
--?   print('top now', State.screen_top1.line)
  Text.redraw_all(State)  -- if we're scrolling, reclaim all fragments to avoid memory leaks
--?   print('pagedown end')
end
function Text.up(State)
  if State.cursor1.pos then
    Text.upA(State)
  else
    Text.upB(State)
  end
end
function Text.upA(State)
--?   print('up', State.cursor1.line, State.cursor1.pos, State.screen_top1.line, State.screen_top1.pos)
  local screen_line_starting_pos, screen_line_index = Text.pos_at_start_of_screen_line(State, State.cursor1)
  if screen_line_starting_pos == 1 then
--?     print('cursor is at first screen line of its line')
    -- line is done; skip to previous text line
    if State.cursor1.line > 1 then
--?       print('found previous text line')
      State.cursor1 = {line=State.cursor1.line-1, pos=nil}
      Text.populate_screen_line_starting_pos(State, State.cursor1.line)
      -- previous text line found, pick its final screen line
--?       print('has multiple screen lines')
      local screen_line_starting_pos = State.line_cache[State.cursor1.line].screen_line_starting_pos
--?       print(#screen_line_starting_pos)
      screen_line_starting_pos = screen_line_starting_pos[#screen_line_starting_pos]
      local screen_line_starting_byte_offset = Text.offset(State.lines[State.cursor1.line].data, screen_line_starting_pos)
      local s = string.sub(State.lines[State.cursor1.line].data, screen_line_starting_byte_offset)
      State.cursor1.pos = screen_line_starting_pos + Text.nearest_cursor_pos(s, State.cursor_x, State.left) - 1
    end
  else
    -- move up one screen line in current line
    assert(screen_line_index > 1)
    local new_screen_line_starting_pos = State.line_cache[State.cursor1.line].screen_line_starting_pos[screen_line_index-1]
    local new_screen_line_starting_byte_offset = Text.offset(State.lines[State.cursor1.line].data, new_screen_line_starting_pos)
    local s = string.sub(State.lines[State.cursor1.line].data, new_screen_line_starting_byte_offset)
    State.cursor1.pos = new_screen_line_starting_pos + Text.nearest_cursor_pos(s, State.cursor_x, State.left) - 1
--?     print('cursor pos is now '..tostring(State.cursor1.pos))
  end
  if Text.lt1(State.cursor1, State.screen_top1) then
    local top2 = Text.to2(State, State.screen_top1)
    top2 = Text.previous_screen_line(State, top2)
    State.screen_top1 = Text.to1(State, top2)
  end
end
function Text.upB(State)
  local line_cache = State.line_cache[State.cursor1.line]
  local screen_line_starting_posB, screen_line_indexB = Text.pos_at_start_of_screen_lineB(State, State.cursor1)
  assert(screen_line_indexB >= 1)
  if screen_line_indexB == 1 then
    -- move to A side of previous line
    if State.cursor1.line > 1 then
      State.cursor1.line = State.cursor1.line-1
      State.cursor1.posB = nil
      Text.populate_screen_line_starting_pos(State, State.cursor1.line)
      local prev_line_cache = State.line_cache[State.cursor1.line]
      local prev_screen_line_starting_pos = prev_line_cache.screen_line_starting_pos[#prev_line_cache.screen_line_starting_pos]
      local prev_screen_line_starting_byte_offset = Text.offset(State.lines[State.cursor1.line].data, prev_screen_line_starting_pos)
      local s = string.sub(State.lines[State.cursor1.line].data, prev_screen_line_starting_byte_offset)
      State.cursor1.pos = prev_screen_line_starting_pos + Text.nearest_cursor_pos(s, State.cursor_x, State.left) - 1
    end
  elseif screen_line_indexB == 2 then
    -- all-B screen-line to potentially A+B screen-line
    local xA = Margin_left + Text.screen_line_width(State, State.cursor1.line, #line_cache.screen_line_starting_pos) + AB_padding
    if State.cursor_x < xA then
      State.cursor1.posB = nil
      Text.populate_screen_line_starting_pos(State, State.cursor1.line)
      local new_screen_line_starting_pos = line_cache.screen_line_starting_pos[#line_cache.screen_line_starting_pos]
      local new_screen_line_starting_byte_offset = Text.offset(State.lines[State.cursor1.line].data, new_screen_line_starting_pos)
      local s = string.sub(State.lines[State.cursor1.line].data, new_screen_line_starting_byte_offset)
      State.cursor1.pos = new_screen_line_starting_pos + Text.nearest_cursor_pos(s, State.cursor_x, State.left) - 1
    else
      Text.populate_screen_line_starting_posB(State, State.cursor1.line)
      local new_screen_line_starting_posB = line_cache.screen_line_starting_posB[screen_line_indexB-1]
      local new_screen_line_starting_byte_offsetB = Text.offset(State.lines[State.cursor1.line].dataB, new_screen_line_starting_posB)
      local s = string.sub(State.lines[State.cursor1.line].dataB, new_screen_line_starting_byte_offsetB)
      State.cursor1.posB = new_screen_line_starting_posB + Text.nearest_cursor_pos(s, State.cursor_x-xA, State.left) - 1
    end
  else
    assert(screen_line_indexB > 2)
    -- all-B screen-line to all-B screen-line
    Text.populate_screen_line_starting_posB(State, State.cursor1.line)
    local new_screen_line_starting_posB = line_cache.screen_line_starting_posB[screen_line_indexB-1]
    local new_screen_line_starting_byte_offsetB = Text.offset(State.lines[State.cursor1.line].dataB, new_screen_line_starting_posB)
    local s = string.sub(State.lines[State.cursor1.line].dataB, new_screen_line_starting_byte_offsetB)
    State.cursor1.posB = new_screen_line_starting_posB + Text.nearest_cursor_pos(s, State.cursor_x, State.left) - 1
  end
  if Text.lt1(State.cursor1, State.screen_top1) then
    local top2 = Text.to2(State, State.screen_top1)
    top2 = Text.previous_screen_line(State, top2)
    State.screen_top1 = Text.to1(State, top2)
  end
end
-- cursor on final screen line (A or B side) => goes to next screen line on A side
-- cursor on A side => move down one screen line (A side) in current line
-- cursor on B side => move down one screen line (B side) in current line
function Text.down(State)
--?   print('down', State.cursor1.line, State.cursor1.pos, State.screen_top1.line, State.screen_top1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)
  if Text.cursor_at_final_screen_line(State) then
    -- line is done, skip to next text line
--?     print('cursor at final screen line of its line')
    if State.cursor1.line < #State.lines then
      State.cursor1 = {
        line = State.cursor1.line+1,
        pos = Text.nearest_cursor_pos(State.lines[State.cursor1.line+1].data, State.cursor_x, State.left)
      }
--?       print(State.cursor1.pos)
    end
    if State.cursor1.line > State.screen_bottom1.line then
--?       print('screen top before:', State.screen_top1.line, State.screen_top1.pos)
--?       print('scroll up preserving cursor')
      Text.snap_cursor_to_bottom_of_screen(State)
--?       print('screen top after:', State.screen_top1.line, State.screen_top1.pos)
    end
  elseif State.cursor1.pos then
    -- move down one screen line (A side) in current line
    local scroll_down = Text.le1(State.screen_bottom1, State.cursor1)
--?     print('cursor is NOT at final screen line of its line')
    local screen_line_starting_pos, screen_line_index = Text.pos_at_start_of_screen_line(State, State.cursor1)
    Text.populate_screen_line_starting_pos(State, State.cursor1.line)
    local new_screen_line_starting_pos = State.line_cache[State.cursor1.line].screen_line_starting_pos[screen_line_index+1]
--?     print('switching pos of screen line at cursor from '..tostring(screen_line_starting_pos)..' to '..tostring(new_screen_line_starting_pos))
    local new_screen_line_starting_byte_offset = Text.offset(State.lines[State.cursor1.line].data, new_screen_line_starting_pos)
    local s = string.sub(State.lines[State.cursor1.line].data, new_screen_line_starting_byte_offset)
    State.cursor1.pos = new_screen_line_starting_pos + Text.nearest_cursor_pos(s, State.cursor_x, State.left) - 1
--?     print('cursor pos is now', State.cursor1.line, State.cursor1.pos)
    if scroll_down then
--?       print('scroll up preserving cursor')
      Text.snap_cursor_to_bottom_of_screen(State)
--?       print('screen top after:', State.screen_top1.line, State.screen_top1.pos)
    end
  else
    -- move down one screen line (B side) in current line
    local scroll_down = false
    if Text.le1(State.screen_bottom1, State.cursor1) then
      scroll_down = true
    end
    local cursor_line = State.lines[State.cursor1.line]
    local cursor_line_cache = State.line_cache[State.cursor1.line]
    local cursor2 = Text.to2(State, State.cursor1)
    assert(cursor2.screen_lineB < #cursor_line_cache.screen_line_starting_posB)
    local screen_line_starting_posB, screen_line_indexB = Text.pos_at_start_of_screen_lineB(State, State.cursor1)
    Text.populate_screen_line_starting_posB(State, State.cursor1.line)
    local new_screen_line_starting_posB = cursor_line_cache.screen_line_starting_posB[screen_line_indexB+1]
    local new_screen_line_starting_byte_offsetB = Text.offset(cursor_line.dataB, new_screen_line_starting_posB)
    local s = string.sub(cursor_line.dataB, new_screen_line_starting_byte_offsetB)
    State.cursor1.posB = new_screen_line_starting_posB + Text.nearest_cursor_pos(s, State.cursor_x, State.left) - 1
    if scroll_down then
      Text.snap_cursor_to_bottom_of_screen(State)
    end
  end
--?   print('=>', State.cursor1.line, State.cursor1.pos, State.screen_top1.line, State.screen_top1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)
end
function Text.start_of_line(State)
  if State.cursor1.pos then
    State.cursor1.pos = 1
  else
    State.cursor1.posB = 1
  end
  if Text.lt1(State.cursor1, State.screen_top1) then
    State.screen_top1 = {line=State.cursor1.line, pos=1}  -- copy
  end
end
function Text.end_of_line(State)
  if State.cursor1.pos then
    State.cursor1.pos = utf8.len(State.lines[State.cursor1.line].data) + 1
  else
    State.cursor1.posB = utf8.len(State.lines[State.cursor1.line].dataB) + 1
  end
  if Text.cursor_out_of_screen(State) then
    Text.snap_cursor_to_bottom_of_screen(State)
  end
end
function Text.word_left(State)
  -- we can cross the fold, so check side A/B one level down
  Text.skip_whitespace_left(State)
  Text.left(State)
  Text.skip_non_whitespace_left(State)
end
function Text.word_right(State)
  -- we can cross the fold, so check side A/B one level down
  Text.skip_whitespace_right(State)
  Text.right(State)
  Text.skip_non_whitespace_right(State)
  if Text.cursor_out_of_screen(State) then
    Text.snap_cursor_to_bottom_of_screen(State)
  end
end
function Text.skip_whitespace_left(State)
  if State.cursor1.pos then
    Text.skip_whitespace_leftA(State)
  else
    Text.skip_whitespace_leftB(State)
  end
end
function Text.skip_non_whitespace_left(State)
  if State.cursor1.pos then
    Text.skip_non_whitespace_leftA(State)
  else
    Text.skip_non_whitespace_leftB(State)
  end
end
function Text.skip_whitespace_leftA(State)
  while true do
    if State.cursor1.pos == 1 then
      break
    end
    if Text.match(State.lines[State.cursor1.line].data, State.cursor1.pos-1, '%S') then
      break
    end
    Text.left(State)
  end
end
function Text.skip_whitespace_leftB(State)
  while true do
    if State.cursor1.posB == 1 then
      break
    end
    if Text.match(State.lines[State.cursor1.line].dataB, State.cursor1.posB-1, '%S') then
      break
    end
    Text.left(State)
  end
end
function Text.skip_non_whitespace_leftA(State)
  while true do
    if State.cursor1.pos == 1 then
      break
    end
    assert(State.cursor1.pos > 1)
    if Text.match(State.lines[State.cursor1.line].data, State.cursor1.pos-1, '%s') then
      break
    end
    Text.left(State)
  end
end
function Text.skip_non_whitespace_leftB(State)
  while true do
    if State.cursor1.posB == 1 then
      break
    end
    assert(State.cursor1.posB > 1)
    if Text.match(State.lines[State.cursor1.line].dataB, State.cursor1.posB-1, '%s') then
      break
    end
    Text.left(State)
  end
end
function Text.skip_whitespace_right(State)
  if State.cursor1.pos then
    Text.skip_whitespace_rightA(State)
  else
    Text.skip_whitespace_rightB(State)
  end
end
function Text.skip_non_whitespace_right(State)
  if State.cursor1.pos then
    Text.skip_non_whitespace_rightA(State)
  else
    Text.skip_non_whitespace_rightB(State)
  end
end
function Text.skip_whitespace_rightA(State)
  while true do
    if State.cursor1.pos > utf8.len(State.lines[State.cursor1.line].data) then
      break
    end
    if Text.match(State.lines[State.cursor1.line].data, State.cursor1.pos, '%S') then
      break
    end
    Text.right_without_scroll(State)
  end
end
function Text.skip_whitespace_rightB(State)
  while true do
    if State.cursor1.posB > utf8.len(State.lines[State.cursor1.line].dataB) then
      break
    end
    if Text.match(State.lines[State.cursor1.line].dataB, State.cursor1.posB, '%S') then
      break
    end
    Text.right_without_scroll(State)
  end
end
function Text.skip_non_whitespace_rightA(State)
  while true do
    if State.cursor1.pos > utf8.len(State.lines[State.cursor1.line].data) then
      break
    end
    if Text.match(State.lines[State.cursor1.line].data, State.cursor1.pos, '%s') then
      break
    end
    Text.right_without_scroll(State)
  end
end
function Text.skip_non_whitespace_rightB(State)
  while true do
    if State.cursor1.posB > utf8.len(State.lines[State.cursor1.line].dataB) then
      break
    end
    if Text.match(State.lines[State.cursor1.line].dataB, State.cursor1.posB, '%s') then
      break
    end
    Text.right_without_scroll(State)
  end
end
function Text.match(s, pos, pat)
  local start_offset = Text.offset(s, pos)
  assert(start_offset)
  local end_offset = Text.offset(s, pos+1)
  assert(end_offset > start_offset)
  local curr = s:sub(start_offset, end_offset-1)
  return curr:match(pat)
end
function Text.left(State)
  if State.cursor1.pos then
    Text.leftA(State)
  else
    Text.leftB(State)
  end
end
function Text.leftA(State)
  if State.cursor1.pos > 1 then
    State.cursor1.pos = State.cursor1.pos-1
  elseif State.cursor1.line > 1 then
    State.cursor1 = {
      line = State.cursor1.line-1,
      pos = utf8.len(State.lines[State.cursor1.line-1].data) + 1,
    }
  end
  if Text.lt1(State.cursor1, State.screen_top1) then
    local top2 = Text.to2(State, State.screen_top1)
    top2 = Text.previous_screen_line(State, top2)
    State.screen_top1 = Text.to1(State, top2)
  end
end
function Text.leftB(State)
  if State.cursor1.posB > 1 then
    State.cursor1.posB = State.cursor1.posB-1
  else
    -- overflow back into A side
    State.cursor1.posB = nil
    State.cursor1.pos = utf8.len(State.lines[State.cursor1.line].data) + 1
  end
  if Text.lt1(State.cursor1, State.screen_top1) then
    local top2 = Text.to2(State, State.screen_top1)
    top2 = Text.previous_screen_line(State, top2)
    State.screen_top1 = Text.to1(State, top2)
  end
end
function Text.right(State)
  Text.right_without_scroll(State)
  if Text.cursor_out_of_screen(State) then
    Text.snap_cursor_to_bottom_of_screen(State)
  end
end
function Text.right_without_scroll(State)
  if State.cursor1.pos then
    Text.right_without_scrollA(State)
  else
    Text.right_without_scrollB(State)
  end
end
function Text.right_without_scrollA(State)
  if State.cursor1.pos <= utf8.len(State.lines[State.cursor1.line].data) then
    State.cursor1.pos = State.cursor1.pos+1
  elseif State.cursor1.line <= #State.lines-1 then
    State.cursor1 = {line=State.cursor1.line+1, pos=1}
  end
end
function Text.right_without_scrollB(State)
  if State.cursor1.posB <= utf8.len(State.lines[State.cursor1.line].dataB) then
    State.cursor1.posB = State.cursor1.posB+1
  elseif State.cursor1.line <= #State.lines-1 then
    -- overflow back into A side
    State.cursor1 = {line=State.cursor1.line+1, pos=1}
  end
end
function Text.pos_at_start_of_screen_line(State, loc1)
  Text.populate_screen_line_starting_pos(State, loc1.line)
  local line_cache = State.line_cache[loc1.line]
  for i=#line_cache.screen_line_starting_pos,1,-1 do
    local spos = line_cache.screen_line_starting_pos[i]
    if spos <= loc1.pos then
      return spos,i
    end
  end
  assert(false)
end
function Text.pos_at_start_of_screen_lineB(State, loc1)
  Text.populate_screen_line_starting_pos(State, loc1.line)
  local line_cache = State.line_cache[loc1.line]
  local x = Margin_left + Text.screen_line_width(State, loc1.line, #line_cache.screen_line_starting_pos) + AB_padding
  Text.populate_screen_line_starting_posB(State, loc1.line, x)
  for i=#line_cache.screen_line_starting_posB,1,-1 do
    local sposB = line_cache.screen_line_starting_posB[i]
    if sposB <= loc1.posB then
      return sposB,i
    end
  end
  assert(false)
end
function Text.cursor_at_final_screen_line(State)
  Text.populate_screen_line_starting_pos(State, State.cursor1.line)
  local line = State.lines[State.cursor1.line]
  local screen_lines = State.line_cache[State.cursor1.line].screen_line_starting_pos
--?   print(screen_lines[#screen_lines], State.cursor1.pos)
  if (not State.expanded and not line.expanded) or
      line.dataB == nil then
    return screen_lines[#screen_lines] <= State.cursor1.pos
  end
  if State.cursor1.pos then
    -- ignore B side
    return screen_lines[#screen_lines] <= State.cursor1.pos
  end
  assert(State.cursor1.posB)
  local line_cache = State.line_cache[State.cursor1.line]
  local x = Margin_left + Text.screen_line_width(State, State.cursor1.line, #line_cache.screen_line_starting_pos) + AB_padding
  Text.populate_screen_line_starting_posB(State, State.cursor1.line, x)
  local screen_lines = State.line_cache[State.cursor1.line].screen_line_starting_posB
  return screen_lines[#screen_lines] <= State.cursor1.posB
end
function Text.move_cursor_down_to_next_text_line_while_scrolling_again_if_necessary(State)
  if State.top > App.screen.height - State.line_height then
--?     print('scroll up')
    Text.snap_cursor_to_bottom_of_screen(State)
  end
end
-- should never modify State.cursor1
function Text.snap_cursor_to_bottom_of_screen(State)
--?   print('to2:', State.cursor1.line, State.cursor1.pos, State.cursor1.posB)
  local top2 = Text.to2(State, State.cursor1)
--?   print('to2: =>', top2.line, top2.screen_line, top2.screen_pos, top2.screen_lineB, top2.screen_posB)
  -- slide to start of screen line
  if top2.screen_pos then
    top2.screen_pos = 1
  else
    assert(top2.screen_posB)
    top2.screen_posB = 1
  end
--?   print('snap', State.screen_top1.line, State.screen_top1.pos, State.screen_top1.posB, State.cursor1.line, State.cursor1.pos, State.cursor1.posB, State.screen_bottom1.line, State.screen_bottom1.pos, State.screen_bottom1.posB)
--?   print('cursor pos '..tostring(State.cursor1.pos)..' is on the #'..tostring(top2.screen_line)..' screen line down')
  local y = App.screen.height - State.line_height
  -- duplicate some logic from love.draw
  while true do
--?     print(y, 'top2:', State.lines[top2.line].data, top2.line, top2.screen_line, top2.screen_pos, top2.screen_lineB, top2.screen_posB)
    if top2.line == 1 and top2.screen_line == 1 then break end
    local h = State.line_height
    if y - h < State.top then
      break
    end
    y = y - h
    top2 = Text.previous_screen_line(State, top2)
  end
--?   print('top2 finally:', top2.line, top2.screen_line, top2.screen_pos)
  State.screen_top1 = Text.to1(State, top2)
--?   print('top1 finally:', State.screen_top1.line, State.screen_top1.pos)
--?   print('snap =>', State.screen_top1.line, State.screen_top1.pos, State.screen_top1.posB, State.cursor1.line, State.cursor1.pos, State.cursor1.posB, State.screen_bottom1.line, State.screen_bottom1.pos, State.screen_bottom1.posB)
  Text.redraw_all(State)  -- if we're scrolling, reclaim all fragments to avoid memory leaks
  Foo = true
end
function Text.in_line(State, line_index, x,y)
  local line = State.lines[line_index]
  local line_cache = State.line_cache[line_index]
  if line_cache.starty == nil then return false end  -- outside current page
  if y < line_cache.starty then return false end
  local num_screen_lines = 0
  if line_cache.startpos then
    Text.populate_screen_line_starting_pos(State, line_index)
    num_screen_lines = num_screen_lines + #line_cache.screen_line_starting_pos - Text.screen_line_index(line_cache.screen_line_starting_pos, line_cache.startpos) + 1
  end
--?   print('#screenlines after A', num_screen_lines)
  if line.dataB and (State.expanded or line.expanded) then
    local x = Margin_left + Text.screen_line_width(State, line_index, #line_cache.screen_line_starting_pos) + AB_padding
    Text.populate_screen_line_starting_posB(State, line_index, x)
--?     print('B:', x, #line_cache.screen_line_starting_posB)
    if line_cache.startposB then
      num_screen_lines = num_screen_lines + #line_cache.screen_line_starting_posB - Text.screen_line_indexB(line_cache.screen_line_starting_posB, line_cache.startposB)  -- no +1; first screen line of B side overlaps with A side
    else
      num_screen_lines = num_screen_lines + #line_cache.screen_line_starting_posB - Text.screen_line_indexB(line_cache.screen_line_starting_posB, 1)  -- no +1; first screen line of B side overlaps with A side
    end
  end
--?   print('#screenlines after B', num_screen_lines)
  return y < line_cache.starty + State.line_height*num_screen_lines
end
-- convert mx,my in pixels to schema-1 coordinates
-- returns: pos, posB
-- scenarios:
--   line without B side
--   line with B side collapsed
--   line with B side expanded
--   line starting rendering in A side (startpos ~= nil)
--   line starting rendering in B side (startposB ~= nil)
--   my on final screen line of A side
--     mx to right of A side with no B side
--     mx to right of A side but left of B side
--     mx to right of B side
-- preconditions:
--  startpos xor startposB
--  expanded -> dataB
function Text.to_pos_on_line(State, line_index, mx, my)
  local line = State.lines[line_index]
  local line_cache = State.line_cache[line_index]
  assert(my >= line_cache.starty)
  -- duplicate some logic from Text.draw
  local y = line_cache.starty
--?   print('click', line_index, my, 'with line starting at', y, #line_cache.screen_line_starting_pos)  -- , #line_cache.screen_line_starting_posB)
  if line_cache.startpos then
    local start_screen_line_index = Text.screen_line_index(line_cache.screen_line_starting_pos, line_cache.startpos)
    for screen_line_index = start_screen_line_index,#line_cache.screen_line_starting_pos do
      local screen_line_starting_pos = line_cache.screen_line_starting_pos[screen_line_index]
      local screen_line_starting_byte_offset = Text.offset(line.data, screen_line_starting_pos)
--?       print('iter', y, screen_line_index, screen_line_starting_pos, string.sub(line.data, screen_line_starting_byte_offset))
      local nexty = y + State.line_height
      if my < nexty then
        -- On all wrapped screen lines but the final one, clicks past end of
        -- line position cursor on final character of screen line.
        -- (The final screen line positions past end of screen line as always.)
        if screen_line_index < #line_cache.screen_line_starting_pos and mx > State.left + Text.screen_line_width(State, line_index, screen_line_index) then
--?           print('past end of non-final line; return')
          return line_cache.screen_line_starting_pos[screen_line_index+1]-1
        end
        local s = string.sub(line.data, screen_line_starting_byte_offset)
--?         print('return', mx, Text.nearest_cursor_pos(s, mx, State.left), '=>', screen_line_starting_pos + Text.nearest_cursor_pos(s, mx, State.left) - 1)
        local screen_line_posA = Text.nearest_cursor_pos(s, mx, State.left)
        if line.dataB == nil then
          -- no B side
          return screen_line_starting_pos + screen_line_posA - 1
        end
        if not State.expanded and not line.expanded then
          -- B side is not expanded
          return screen_line_starting_pos + screen_line_posA - 1
        end
        local lenA = utf8.len(s)
        if screen_line_posA < lenA then
          -- mx is within A side
          return screen_line_starting_pos + screen_line_posA - 1
        end
        local max_xA = State.left+Text.x(s, lenA+1)
        if mx < max_xA + AB_padding then
          -- mx is in the space between A and B side
          return screen_line_starting_pos + screen_line_posA - 1
        end
        mx = mx - max_xA - AB_padding
        local screen_line_posB = Text.nearest_cursor_pos(line.dataB, mx, --[[no left margin]] 0)
        return nil, screen_line_posB
      end
      y = nexty
    end
  end
  -- look in screen lines composed entirely of the B side
  assert(State.expanded or line.expanded)
  local start_screen_line_indexB
  if line_cache.startposB then
    start_screen_line_indexB = Text.screen_line_indexB(line_cache.screen_line_starting_posB, line_cache.startposB)
  else
    start_screen_line_indexB = 2  -- skip the first line of side B, which we checked above
  end
  for screen_line_indexB = start_screen_line_indexB,#line_cache.screen_line_starting_posB do
    local screen_line_starting_posB = line_cache.screen_line_starting_posB[screen_line_indexB]
    local screen_line_starting_byte_offsetB = Text.offset(line.dataB, screen_line_starting_posB)
--?     print('iter2', y, screen_line_indexB, screen_line_starting_posB, string.sub(line.dataB, screen_line_starting_byte_offsetB))
    local nexty = y + State.line_height
    if my < nexty then
      -- On all wrapped screen lines but the final one, clicks past end of
      -- line position cursor on final character of screen line.
      -- (The final screen line positions past end of screen line as always.)
--?       print('aa', mx, State.left, Text.screen_line_widthB(State, line_index, screen_line_indexB))
      if screen_line_indexB < #line_cache.screen_line_starting_posB and mx > State.left + Text.screen_line_widthB(State, line_index, screen_line_indexB) then
--?         print('past end of non-final line; return')
        return nil, line_cache.screen_line_starting_posB[screen_line_indexB+1]-1
      end
      local s = string.sub(line.dataB, screen_line_starting_byte_offsetB)
--?       print('return', mx, Text.nearest_cursor_pos(s, mx, State.left), '=>', screen_line_starting_posB + Text.nearest_cursor_pos(s, mx, State.left) - 1)
      return nil, screen_line_starting_posB + Text.nearest_cursor_pos(s, mx, State.left) - 1
    end
    y = nexty
  end
  assert(false)
end
function Text.screen_line_width(State, line_index, i)
  local line = State.lines[line_index]
  local line_cache = State.line_cache[line_index]
  local start_pos = line_cache.screen_line_starting_pos[i]
  local start_offset = Text.offset(line.data, start_pos)
  local screen_line
  if i < #line_cache.screen_line_starting_pos then
    local past_end_pos = line_cache.screen_line_starting_pos[i+1]
    local past_end_offset = Text.offset(line.data, past_end_pos)
    screen_line = string.sub(line.data, start_offset, past_end_offset-1)
  else
    screen_line = string.sub(line.data, start_pos)
  end
  local screen_line_text = App.newText(love.graphics.getFont(), screen_line)
  return App.width(screen_line_text)
end
function Text.screen_line_widthB(State, line_index, i)
  local line = State.lines[line_index]
  local line_cache = State.line_cache[line_index]
  local start_posB = line_cache.screen_line_starting_posB[i]
  local start_offsetB = Text.offset(line.dataB, start_posB)
  local screen_line
  if i < #line_cache.screen_line_starting_posB then
--?     print('non-final', i)
    local past_end_posB = line_cache.screen_line_starting_posB[i+1]
    local past_end_offsetB = Text.offset(line.dataB, past_end_posB)
--?     print('between', start_offsetB, past_end_offsetB)
    screen_line = string.sub(line.dataB, start_offsetB, past_end_offsetB-1)
  else
--?     print('final', i)
--?     print('after', start_offsetB)
    screen_line = string.sub(line.dataB, start_offsetB)
  end
  local screen_line_text = App.newText(love.graphics.getFont(), screen_line)
--?   local result = App.width(screen_line_text)
--?   print('=>', result)
--?   return result
  return App.width(screen_line_text)
end
function Text.screen_line_index(screen_line_starting_pos, pos)
  for i = #screen_line_starting_pos,1,-1 do
    if screen_line_starting_pos[i] <= pos then
      return i
    end
  end
end
function Text.screen_line_indexB(screen_line_starting_posB, posB)
  if posB == nil then
    return 0
  end
  assert(screen_line_starting_posB)
  for i = #screen_line_starting_posB,1,-1 do
    if screen_line_starting_posB[i] <= posB then
      return i
    end
  end
end
-- convert x pixel coordinate to pos
-- oblivious to wrapping
-- result: 1 to len+1
function Text.nearest_cursor_pos(line, x, left)
  if x < left then
    return 1
  end
  local len = utf8.len(line)
  local max_x = left+Text.x(line, len+1)
  if x > max_x then
    return len+1
  end
  local leftpos, rightpos = 1, len+1
--?   print('-- nearest', x)
  while true do
--?     print('nearest', x, '^'..line..'$', leftpos, rightpos)
    if leftpos == rightpos then
      return leftpos
    end
    local curr = math.floor((leftpos+rightpos)/2)
    local currxmin = left+Text.x(line, curr)
    local currxmax = left+Text.x(line, curr+1)
--?     print('nearest', x, leftpos, rightpos, curr, currxmin, currxmax)
    if currxmin <= x and x < currxmax then
      if x-currxmin < currxmax-x then
        return curr
      else
        return curr+1
      end
    end
    if leftpos >= rightpos-1 then
      return rightpos
    end
    if currxmin > x then
      rightpos = curr
    else
      leftpos = curr
    end
  end
  assert(false)
end
-- return the nearest index of line (in utf8 code points) which lies entirely
-- within x pixels of the left margin
-- result: 0 to len+1
function Text.nearest_pos_less_than(line, x)
--?   print('', '-- nearest_pos_less_than', line, x)
  local len = utf8.len(line)
  local max_x = Text.x_after(line, len)
  if x > max_x then
    return len+1
  end
  local left, right = 0, len+1
  while true do
    local curr = math.floor((left+right)/2)
    local currxmin = Text.x_after(line, curr+1)
    local currxmax = Text.x_after(line, curr+2)
--?     print('', x, left, right, curr, currxmin, currxmax)
    if currxmin <= x and x < currxmax then
      return curr
    end
    if left >= right-1 then
      return left
    end
    if currxmin > x then
      right = curr
    else
      left = curr
    end
  end
  assert(false)
end
function Text.x_after(s, pos)
  local offset = Text.offset(s, math.min(pos+1, #s+1))
  local s_before = s:sub(1, offset-1)
--?   print('^'..s_before..'$')
  local text_before = App.newText(love.graphics.getFont(), s_before)
  return App.width(text_before)
end
function Text.x(s, pos)
  local offset = Text.offset(s, pos)
  local s_before = s:sub(1, offset-1)
  local text_before = App.newText(love.graphics.getFont(), s_before)
  return App.width(text_before)
end
function Text.to2(State, loc1)
  if loc1.pos then
    return Text.to2A(State, loc1)
  else
    return Text.to2B(State, loc1)
  end
end
function Text.to2A(State, loc1)
  local result = {line=loc1.line}
  local line_cache = State.line_cache[loc1.line]
  Text.populate_screen_line_starting_pos(State, loc1.line)
  for i=#line_cache.screen_line_starting_pos,1,-1 do
    local spos = line_cache.screen_line_starting_pos[i]
    if spos <= loc1.pos then
      result.screen_line = i
      result.screen_pos = loc1.pos - spos + 1
      break
    end
  end
  assert(result.screen_pos)
  return result
end
function Text.to2B(State, loc1)
  local result = {line=loc1.line}
  local line_cache = State.line_cache[loc1.line]
  Text.populate_screen_line_starting_pos(State, loc1.line)
  local x = Margin_left + Text.screen_line_width(State, loc1.line, #line_cache.screen_line_starting_pos) + AB_padding
  Text.populate_screen_line_starting_posB(State, loc1.line, x)
  for i=#line_cache.screen_line_starting_posB,1,-1 do
    local sposB = line_cache.screen_line_starting_posB[i]
    if sposB <= loc1.posB then
      result.screen_lineB = i
      result.screen_posB = loc1.posB - sposB + 1
      break
    end
  end
  assert(result.screen_posB)
  return result
end
function Text.to1(State, loc2)
  if loc2.screen_pos then
    return Text.to1A(State, loc2)
  else
    return Text.to1B(State, loc2)
  end
end
function Text.to1A(State, loc2)
  local result = {line=loc2.line, pos=loc2.screen_pos}
  if loc2.screen_line > 1 then
    result.pos = State.line_cache[loc2.line].screen_line_starting_pos[loc2.screen_line] + loc2.screen_pos - 1
  end
  return result
end
function Text.to1B(State, loc2)
  local result = {line=loc2.line, posB=loc2.screen_posB}
  if loc2.screen_lineB > 1 then
    result.posB = State.line_cache[loc2.line].screen_line_starting_posB[loc2.screen_lineB] + loc2.screen_posB - 1
  end
  return result
end
function Text.lt1(a, b)
  if a.line < b.line then
    return true
  end
  if a.line > b.line then
    return false
  end
  -- A side < B side
  if a.pos and not b.pos then
    return true
  end
  if not a.pos and b.pos then
    return false
  end
  if a.pos then
    return a.pos < b.pos
  else
    return a.posB < b.posB
  end
end
function Text.le1(a, b)
  return eq(a, b) or Text.lt1(a, b)
end
function Text.offset(s, pos1)
  if pos1 == 1 then return 1 end
  local result = utf8.offset(s, pos1)
  if result == nil then
    print(pos1, #s, s)
  end
  assert(result)
  return result
end
function Text.previous_screen_line(State, loc2)
  if loc2.screen_pos then
    return Text.previous_screen_lineA(State, loc2)
  else
    return Text.previous_screen_lineB(State, loc2)
  end
end
function Text.previous_screen_lineA(State, loc2)
  if loc2.screen_line > 1 then
--?     print('a')
    return {line=loc2.line, screen_line=loc2.screen_line-1, screen_pos=1}
  elseif loc2.line == 1 then
--?     print('b')
    return loc2
  else
    Text.populate_screen_line_starting_pos(State, loc2.line-1)
    if State.lines[loc2.line-1].dataB == nil or
        (not State.expanded and not State.lines[loc2.line-1].expanded) then
--?       print('c1', loc2.line-1, State.lines[loc2.line-1].data, '==', State.lines[loc2.line-1].dataB, State.line_cache[loc2.line-1].fragmentsB)
      return {line=loc2.line-1, screen_line=#State.line_cache[loc2.line-1].screen_line_starting_pos, screen_pos=1}
    end
    -- try to switch to B
    local prev_line_cache = State.line_cache[loc2.line-1]
    local x = Margin_left + Text.screen_line_width(State, loc2.line-1, #prev_line_cache.screen_line_starting_pos) + AB_padding
    Text.populate_screen_line_starting_posB(State, loc2.line-1, x)
    local screen_line_starting_posB = State.line_cache[loc2.line-1].screen_line_starting_posB
--?     print('c', loc2.line-1, State.lines[loc2.line-1].data, '==', State.lines[loc2.line-1].dataB, '==', #screen_line_starting_posB, 'starting from x', x)
    if #screen_line_starting_posB > 1 then
--?       print('c2')
      return {line=loc2.line-1, screen_lineB=#State.line_cache[loc2.line-1].screen_line_starting_posB, screen_posB=1}
    else
--?       print('c3')
      -- if there's only one screen line, assume it overlaps with A, so remain in A
      return {line=loc2.line-1, screen_line=#State.line_cache[loc2.line-1].screen_line_starting_pos, screen_pos=1}
    end
  end
end
function Text.previous_screen_lineB(State, loc2)
  if loc2.screen_lineB > 2 then  -- first screen line of B side overlaps with A side
    return {line=loc2.line, screen_lineB=loc2.screen_lineB-1, screen_posB=1}
  else
    -- switch to A side
    -- TODO: handle case where fold lands precisely at end of a new screen-line
    return {line=loc2.line, screen_line=#State.line_cache[loc2.line].screen_line_starting_pos, screen_pos=1}
  end
end
-- resize helper
function Text.tweak_screen_top_and_cursor(State)
  if State.screen_top1.pos == 1 then return end
  Text.populate_screen_line_starting_pos(State, State.screen_top1.line)
  local line = State.lines[State.screen_top1.line]
  local line_cache = State.line_cache[State.screen_top1.line]
  for i=2,#line_cache.screen_line_starting_pos do
    local pos = line_cache.screen_line_starting_pos[i]
    if pos == State.screen_top1.pos then
      break
    end
    if pos > State.screen_top1.pos then
      -- make sure screen top is at start of a screen line
      local prev = line_cache.screen_line_starting_pos[i-1]
      if State.screen_top1.pos - prev < pos - State.screen_top1.pos then
        State.screen_top1.pos = prev
      else
        State.screen_top1.pos = pos
      end
      break
    end
  end
  -- make sure cursor is on screen
  if Text.lt1(State.cursor1, State.screen_top1) then
    State.cursor1 = {line=State.screen_top1.line, pos=State.screen_top1.pos}
  elseif State.cursor1.line >= State.screen_bottom1.line then
--?     print('too low')
    if Text.cursor_out_of_screen(State) then
--?       print('tweak')
      local pos,posB = Text.to_pos_on_line(State, State.screen_bottom1.line, State.right-5, App.screen.height-5)
      State.cursor1 = {line=State.screen_bottom1.line, pos=pos, posB=posB}
    end
  end
end
-- slightly expensive since it redraws the screen
function Text.cursor_out_of_screen(State)
  App.draw()
  return State.cursor_y == nil
  -- this approach is cheaper and almost works, except on the final screen
  -- where file ends above bottom of screen
--?   local botpos = Text.pos_at_start_of_screen_line(State, State.cursor1)
--?   local botline1 = {line=State.cursor1.line, pos=botpos}
--?   return Text.lt1(State.screen_bottom1, botline1)
end
function Text.redraw_all(State)
--?   print('clearing fragments')
  State.line_cache = {}
  for i=1,#State.lines do
    State.line_cache[i] = {}
  end
end
function Text.clear_screen_line_cache(State, line_index)
  State.line_cache[line_index].fragments = nil
  State.line_cache[line_index].fragmentsB = nil
  State.line_cache[line_index].screen_line_starting_pos = nil
  State.line_cache[line_index].screen_line_starting_posB = nil
end
function trim(s)
  return s:gsub('^%s+', ''):gsub('%s+$', '')
end
function ltrim(s)
  return s:gsub('^%s+', '')
end
function rtrim(s)
  return s:gsub('%s+$', '')
end

function test_resize_window()
  io.write('\ntest_resize_window')
  App.screen.init{width=300, height=300}
  Editor_state = edit.initialize_test_state()
  Editor_state.filename = 'foo'
  Log_browser_state = edit.initialize_test_state()
  check_eq(App.screen.width, 300, 'F - test_resize_window/baseline/width')
  check_eq(App.screen.height, 300, 'F - test_resize_window/baseline/height')
  check_eq(Editor_state.left, Test_margin_left, 'F - test_resize_window/baseline/left_margin')
  App.resize(200, 400)
  check_eq(App.screen.width, 200, 'F - test_resize_window/width')
  check_eq(App.screen.height, 400, 'F - test_resize_window/height')
  check_eq(Editor_state.left, Test_margin_left, 'F - test_resize_window/left_margin')
  -- ugly; right margin switches from 0 after resize
  check_eq(Editor_state.right, 200-Margin_right, 'F - test_resize_window/right_margin')
  check_eq(Editor_state.width, 200-Test_margin_left-Margin_right, 'F - test_resize_window/drawing_width')
  -- TODO: how to make assertions about when App.update got past the early exit?
end
function test_drop_file()
  io.write('\ntest_drop_file')
  App.screen.init{width=Editor_state.left+300, height=300}
  Editor_state = edit.initialize_test_state()
  App.filesystem['foo'] = 'abc\ndef\nghi\n'
  local fake_dropped_file = {
    opened = false,
    getFilename = function(self)
                    return 'foo'
                  end,
    open = function(self)
             self.opened = true
           end,
    lines = function(self)
              assert(self.opened)
              return App.filesystem['foo']:gmatch('[^\n]+')
            end,
    close = function(self)
              self.opened = false
            end,
  }
  App.filedropped(fake_dropped_file)
  check_eq(#Editor_state.lines, 3, 'F - test_drop_file/#lines')
  check_eq(Editor_state.lines[1].data, 'abc', 'F - test_drop_file/lines:1')
  check_eq(Editor_state.lines[2].data, 'def', 'F - test_drop_file/lines:2')
  check_eq(Editor_state.lines[3].data, 'ghi', 'F - test_drop_file/lines:3')
  edit.draw(Editor_state)
end
function test_drop_file_saves_previous()
  io.write('\ntest_drop_file_saves_previous')
  App.screen.init{width=Editor_state.left+300, height=300}
  -- initially editing a file called foo that hasn't been saved to filesystem yet
  Editor_state.lines = load_array{'abc', 'def'}
  Editor_state.filename = 'foo'
  schedule_save(Editor_state)
  -- now drag a new file bar from the filesystem
  App.filesystem['bar'] = 'abc\ndef\nghi\n'
  local fake_dropped_file = {
    opened = false,
    getFilename = function(self)
                    return 'bar'
                  end,
    open = function(self)
             self.opened = true
           end,
    lines = function(self)
              assert(self.opened)
              return App.filesystem['bar']:gmatch('[^\n]+')
            end,
    close = function(self)
              self.opened = false
            end,
  }
  App.filedropped(fake_dropped_file)
  -- filesystem now contains a file called foo
  check_eq(App.filesystem['foo'], 'abc\ndef\n', 'F - test_drop_file_saves_previous')
end

-- primitives for saving to file and loading from file
Fold = '\x1e'  -- ASCII RS (record separator)
function file_exists(filename)
  local infile = App.open_for_reading(filename)
  if infile then
    infile:close()
    return true
  else
    return false
  end
end
function load_from_disk(State)
  local infile = App.open_for_reading(State.filename)
  State.lines = load_from_file(infile)
  if infile then infile:close() end
end
function load_from_file(infile)
  local result = {}
  if infile then
    local infile_next_line = infile:lines()  -- works with both Lua files and LÖVE Files (https://www.love2d.org/wiki/File)
    while true do
      local line = infile_next_line()
      if line == nil then break end
      local line_info = {}
      if line:find(Fold) then
        _, _, line_info.data, line_info.dataB = line:find('([^'..Fold..']*)'..Fold..'([^'..Fold..']*)')
      else
        line_info.data = line
      end
      table.insert(result, line_info)
    end
  end
  if #result == 0 then
    table.insert(result, {data=''})
  end
  return result
end
function save_to_disk(State)
  local outfile = App.open_for_writing(State.filename)
  if outfile == nil then
    error('failed to write to "'..State.filename..'"')
  end
  for _,line in ipairs(State.lines) do
    outfile:write(line.data)
    if line.dataB and #line.dataB > 0 then
      outfile:write(Fold)
      outfile:write(line.dataB)
    end
    outfile:write('\n')
  end
  outfile:close()
end
function file_exists(filename)
  local infile = App.open_for_reading(filename)
  if infile then
    infile:close()
    return true
  else
    return false
  end
end
-- for tests
function load_array(a)
  local result = {}
  local next_line = ipairs(a)
  local i,line,drawing = 0, ''
  while true do
    i,line = next_line(a, i)
    if i == nil then break end
    local line_info = {}
    if line:find(Fold) then
      _, _, line_info.data, line_info.dataB = line:find('([^'..Fold..']*)'..Fold..'([^'..Fold..']*)')
    else
      line_info.data = line
    end
    table.insert(result, line_info)
  end
  if #result == 0 then
    table.insert(result, {data=''})
  end
  return result
end

-- some constants people might like to tweak
Text_color = {r=0, g=0, b=0}
Cursor_color = {r=1, g=0, b=0}
Focus_stroke_color = {r=1, g=0, b=0}  -- what mouse is hovering over
Highlight_color = {r=0.7, g=0.7, b=0.9}  -- selected text
Fold_color = {r=0, g=0.6, b=0}
Fold_background_color = {r=0, g=0.7, b=0}
Margin_top = 15
Margin_left = 25
Margin_right = 25
edit = {}
-- run in both tests and a real run
function edit.initialize_state(top, left, right, font_height, line_height)  -- currently always draws to bottom of screen
  local result = {
    -- a line of bifold text consists of an A side and an optional B side, each of which is a string
    -- expanded: whether to show B side
    lines = {{data='', dataB=nil, expanded=nil}},  -- array of lines
    -- Lines can be too long to fit on screen, in which case they _wrap_ into
    -- multiple _screen lines_.
    -- rendering wrapped text lines needs some additional short-lived data per line:
    --   startpos, the index of data the line starts rendering from, can only be >1 for topmost line on screen
    --   starty, the y coord in pixels the line starts rendering from
    --   fragments: snippets of rendered love.graphics.Text, guaranteed to not straddle screen lines
    --   screen_line_starting_pos: optional array of grapheme indices if it wraps over more than one screen line
    line_cache = {},
    -- Given wrapping, any potential location for the text cursor can be described in two ways:
    -- * schema 1: As a combination of line index and position within a line (in utf8 codepoint units)
    -- * schema 2: As a combination of line index, screen line index within the line, and a position within the screen line.
    -- Positions (and screen line indexes) can be in either the A or the B side.
    --
    -- Most of the time we'll only persist positions in schema 1, translating to
    -- schema 2 when that's convenient.
    --
    -- Make sure these coordinates are never aliased, so that changing one causes
    -- action at a distance.
    screen_top1 = {line=1, pos=1, posB=nil},  -- position of start of screen line at top of screen
    cursor1 = {line=1, pos=1, posB=nil},  -- position of cursor
    screen_bottom1 = {line=1, pos=1, posB=nil},  -- position of start of screen line at bottom of screen
    -- cursor coordinates in pixels
    cursor_x = 0,
    cursor_y = 0,
    font_height = font_height,
    line_height = line_height,
    em = App.newText(love.graphics.getFont(), 'm'),  -- widest possible character width
    top = top,
    left = left,
    right = right,
    width = right-left,
    filename = love.filesystem.getUserDirectory()..'/lines.txt',
    next_save = nil,
    -- undo
    history = {},
    next_history = 1,
    -- search
    search_term = nil,
    search_text = nil,
    search_backup = nil,  -- stuff to restore when cancelling search
  }
  return result
end  -- App.initialize_state
function edit.draw(State)
  State.button_handlers = {}
  App.color(Text_color)
  assert(#State.lines == #State.line_cache)
  if not Text.le1(State.screen_top1, State.cursor1) then
    print(State.screen_top1.line, State.screen_top1.pos, State.screen_top1.posB, State.cursor1.line, State.cursor1.pos, State.cursor1.posB)
    assert(false)
  end
  State.cursor_x = nil
  State.cursor_y = nil
  local y = State.top
--?   print('== draw')
  for line_index = State.screen_top1.line,#State.lines do
    local line = State.lines[line_index]
--?     print('draw:', y, line_index, line)
    if y + State.line_height > App.screen.height then break end
    State.screen_bottom1 = {line=line_index, pos=nil, posB=nil}
--?     print('text.draw', y, line_index)
    local startpos, startposB = 1, nil
    if line_index == State.screen_top1.line then
      if State.screen_top1.pos then
        startpos = State.screen_top1.pos
      else
        startpos, startposB = nil, State.screen_top1.posB
      end
    end
    y, State.screen_bottom1.pos, State.screen_bottom1.posB = Text.draw(State, line_index, y, startpos, startposB)
    y = y + State.line_height
--?     print('=> y', y)
  end
  if State.search_term then
    Text.draw_search_bar(State)
  end
end
function edit.update(State, dt)
  if State.next_save and State.next_save < App.getTime() then
    save_to_disk(State)
    State.next_save = nil
  end
end
function schedule_save(State)
  if State.next_save == nil then
    State.next_save = App.getTime() + 3  -- short enough that you're likely to still remember what you did
  end
end
function edit.quit(State)
  -- make sure to save before quitting
  if State.next_save then
    save_to_disk(State)
  end
end
function edit.mouse_pressed(State, x,y, mouse_button)
  if State.search_term then return end
--?   print('press', State.selection1.line, State.selection1.pos)
  if mouse_press_consumed_by_any_button_handler(State, x,y, mouse_button) then
    -- press on a button and it returned 'true' to short-circuit
    return
  end
  for line_index,line in ipairs(State.lines) do
    if Text.in_line(State, line_index, x,y) then
      local pos,posB = Text.to_pos_on_line(State, line_index, x, y)
--?       print(x,y, 'setting cursor:', line_index, pos, posB)
      State.cursor1 = {line=line_index, pos=pos, posB=posB}
      break
    end
  end
end
function edit.mouse_released(State, x,y, mouse_button)
end
function edit.textinput(State, t)
  for _,line_cache in ipairs(State.line_cache) do line_cache.starty = nil end  -- just in case we scroll
  if State.search_term then
    State.search_term = State.search_term..t
    State.search_text = nil
    Text.search_next(State)
  else
    Text.textinput(State, t)
  end
  schedule_save(State)
end
function edit.keychord_pressed(State, chord, key)
  if State.search_term then
    if chord == 'escape' then
      State.search_term = nil
      State.search_text = nil
      State.cursor1 = State.search_backup.cursor
      State.screen_top1 = State.search_backup.screen_top
      State.search_backup = nil
      Text.redraw_all(State)  -- if we're scrolling, reclaim all fragments to avoid memory leaks
    elseif chord == 'return' then
      State.search_term = nil
      State.search_text = nil
      State.search_backup = nil
    elseif chord == 'backspace' then
      local len = utf8.len(State.search_term)
      local byte_offset = Text.offset(State.search_term, len)
      State.search_term = string.sub(State.search_term, 1, byte_offset-1)
      State.search_text = nil
    elseif chord == 'down' then
      if State.cursor1.pos then
        State.cursor1.pos = State.cursor1.pos+1
      else
        State.cursor1.posB = State.cursor1.posB+1
      end
      Text.search_next(State)
    elseif chord == 'up' then
      Text.search_previous(State)
    end
    return
  elseif chord == 'C-f' then
    State.search_term = ''
    State.search_backup = {
      cursor={line=State.cursor1.line, pos=State.cursor1.pos, posB=State.cursor1.posB},
      screen_top={line=State.screen_top1.line, pos=State.screen_top1.pos, posB=State.screen_top1.posB},
    }
    assert(State.search_text == nil)
  -- bifold text
  elseif chord == 'C-b' then
    State.expanded = not State.expanded
    Text.redraw_all(State)
    if not State.expanded then
      for _,line in ipairs(State.lines) do
        line.expanded = nil
      end
      edit.eradicate_locations_after_the_fold(State)
    end
  elseif chord == 'C-d' then
    if State.cursor1.posB == nil then
      local before = snapshot(State, State.cursor1.line)
      if State.lines[State.cursor1.line].dataB == nil then
        State.lines[State.cursor1.line].dataB = ''
      end
      State.lines[State.cursor1.line].expanded = true
      State.cursor1.pos = nil
      State.cursor1.posB = 1
      if Text.cursor_out_of_screen(State) then
        Text.snap_cursor_to_bottom_of_screen(State, State.left, State.right)
      end
      schedule_save(State)
      record_undo_event(State, {before=before, after=snapshot(State, State.cursor1.line)})
    end
  -- zoom
  elseif chord == 'C-=' then
    edit.update_font_settings(State, State.font_height+2)
    Text.redraw_all(State)
  elseif chord == 'C--' then
    edit.update_font_settings(State, State.font_height-2)
    Text.redraw_all(State)
  elseif chord == 'C-0' then
    edit.update_font_settings(State, 20)
    Text.redraw_all(State)
  -- undo
  elseif chord == 'C-z' then
    for _,line_cache in ipairs(State.line_cache) do line_cache.starty = nil end  -- just in case we scroll
    local event = undo_event(State)
    if event then
      local src = event.before
      State.screen_top1 = deepcopy(src.screen_top)
      State.cursor1 = deepcopy(src.cursor)
      patch(State.lines, event.after, event.before)
      patch_placeholders(State.line_cache, event.after, event.before)
      -- if we're scrolling, reclaim all fragments to avoid memory leaks
      Text.redraw_all(State)
      schedule_save(State)
    end
  elseif chord == 'C-y' then
    for _,line_cache in ipairs(State.line_cache) do line_cache.starty = nil end  -- just in case we scroll
    local event = redo_event(State)
    if event then
      local src = event.after
      State.screen_top1 = deepcopy(src.screen_top)
      State.cursor1 = deepcopy(src.cursor)
      patch(State.lines, event.before, event.after)
      -- if we're scrolling, reclaim all fragments to avoid memory leaks
      Text.redraw_all(State)
      schedule_save(State)
    end
  -- clipboard
  elseif chord == 'C-c' then
    local s = Text.selection(State)
    if s then
      App.setClipboardText(s)
    end
  elseif chord == 'C-x' then
    for _,line_cache in ipairs(State.line_cache) do line_cache.starty = nil end  -- just in case we scroll
    local s = Text.cut_selection(State, State.left, State.right)
    if s then
      App.setClipboardText(s)
    end
    schedule_save(State)
  elseif chord == 'C-v' then
    for _,line_cache in ipairs(State.line_cache) do line_cache.starty = nil end  -- just in case we scroll
    -- We don't have a good sense of when to scroll, so we'll be conservative
    -- and sometimes scroll when we didn't quite need to.
    local before_line = State.cursor1.line
    local before = snapshot(State, before_line)
    local clipboard_data = App.getClipboardText()
    for _,code in utf8.codes(clipboard_data) do
      local c = utf8.char(code)
      if c == '\n' then
        Text.insert_return(State)
      else
        Text.insert_at_cursor(State, c)
      end
    end
    if Text.cursor_out_of_screen(State) then
      Text.snap_cursor_to_bottom_of_screen(State, State.left, State.right)
    end
    schedule_save(State)
    record_undo_event(State, {before=before, after=snapshot(State, before_line, State.cursor1.line)})
  -- dispatch to text
  else
    for _,line_cache in ipairs(State.line_cache) do line_cache.starty = nil end  -- just in case we scroll
    Text.keychord_pressed(State, chord)
  end
end
function edit.eradicate_locations_after_the_fold(State)
  -- eradicate side B from any locations we track
  if State.cursor1.posB then
    State.cursor1.posB = nil
    State.cursor1.pos = utf8.len(State.lines[State.cursor1.line].data)
    State.cursor1.pos = Text.pos_at_start_of_screen_line(State, State.cursor1)
  end
  if State.screen_top1.posB then
    State.screen_top1.posB = nil
    State.screen_top1.pos = utf8.len(State.lines[State.screen_top1.line].data)
    State.screen_top1.pos = Text.pos_at_start_of_screen_line(State, State.screen_top1)
  end
end
function edit.key_released(State, key, scancode)
end
function edit.update_font_settings(State, font_height)
  State.font_height = font_height
  love.graphics.setFont(love.graphics.newFont(Editor_state.font_height))
  State.line_height = math.floor(font_height*1.3)
  State.em = App.newText(love.graphics.getFont(), 'm')
  Text_cache = {}
end
--== some methods for tests
Test_margin_left = 25
function edit.initialize_test_state()
  -- if you change these values, tests will start failing
  return edit.initialize_state(
      15,  -- top margin
      Test_margin_left,
      App.screen.width,  -- right margin = 0
      14,  -- font height assuming default LÖVE font
      15)  -- line height
end
-- all textinput events are also keypresses
-- TODO: handle chords of multiple keys
function edit.run_after_textinput(State, t)
  edit.keychord_pressed(State, t)
  edit.textinput(State, t)
  edit.key_released(State, t)
  App.screen.contents = {}
  edit.draw(State)
end
-- not all keys are textinput
function edit.run_after_keychord(State, chord)
  edit.keychord_pressed(State, chord)
  edit.key_released(State, chord)
  App.screen.contents = {}
  edit.draw(State)
end
function edit.run_after_mouse_click(State, x,y, mouse_button)
  App.fake_mouse_press(x,y, mouse_button)
  edit.mouse_pressed(State, x,y, mouse_button)
  App.fake_mouse_release(x,y, mouse_button)
  edit.mouse_released(State, x,y, mouse_button)
  App.screen.contents = {}
  edit.draw(State)
end
function edit.run_after_mouse_press(State, x,y, mouse_button)
  App.fake_mouse_press(x,y, mouse_button)
  edit.mouse_pressed(State, x,y, mouse_button)
  App.screen.contents = {}
  edit.draw(State)
end
function edit.run_after_mouse_release(State, x,y, mouse_button)
  App.fake_mouse_release(x,y, mouse_button)
  edit.mouse_released(State, x,y, mouse_button)
  App.screen.contents = {}
  edit.draw(State)
end

source = {}
Editor_state = {}
-- called both in tests and real run
function source.initialize_globals()
  -- tests currently mostly clear their own state
  Show_log_browser_side = false
  Focus = 'edit'
  Show_file_navigator = false
  File_navigation = {
    candidates = {
      'run',
      'run_tests',
      'log',
      'edit',
      'text',
      'search',
      'select',
      'undo',
      'text_tests',
      'file',
      'source',
      'source_tests',
      'commands',
      'log_browser',
      'source_edit',
      'source_text',
      'source_undo',
      'colorize',
      'source_text_tests',
      'source_file',
      'main',
      'button',
      'keychord',
      'app',
      'test',
      'json',
    },
    index = 1,
  }
  Menu_status_bar_height = nil  -- initialized below
  -- a few text objects we can avoid recomputing unless the font changes
  Text_cache = {}
  -- blinking cursor
  Cursor_time = 0
end
-- called only for real run
function source.initialize()
  love.keyboard.setTextInput(true)  -- bring up keyboard on touch screen
  love.keyboard.setKeyRepeat(true)
  love.graphics.setBackgroundColor(1,1,1)
  if Settings and Settings.source then
    source.load_settings()
  else
    source.initialize_default_settings()
  end
  source.initialize_edit_side{'run.lua'}
  source.initialize_log_browser_side()
  Menu_status_bar_height = 5 + Editor_state.line_height + 5
  Editor_state.top = Editor_state.top + Menu_status_bar_height
  Log_browser_state.top = Log_browser_state.top + Menu_status_bar_height
end
-- environment for a mutable file of bifolded text
-- TODO: some initialization is also happening in load_settings/initialize_default_settings. Clean that up.
function source.initialize_edit_side(arg)
  if #arg > 0 then
    Editor_state.filename = arg[1]
    load_from_disk(Editor_state)
    Text.redraw_all(Editor_state)
    Editor_state.screen_top1 = {line=1, pos=1}
    Editor_state.cursor1 = {line=1, pos=1}
  else
    load_from_disk(Editor_state)
    Text.redraw_all(Editor_state)
  end
  if #arg > 1 then
    print('ignoring commandline args after '..arg[1])
  end
  -- We currently start out with side B collapsed.
  -- Other options:
  --  * save all expanded state by line
  --  * expand all if any location is in side B
  if Editor_state.cursor1.line > #Editor_state.lines then
    Editor_state.cursor1 = {line=1, pos=1}
  end
  if Editor_state.screen_top1.line > #Editor_state.lines then
    Editor_state.screen_top1 = {line=1, pos=1}
  end
  edit.eradicate_locations_after_the_fold(Editor_state)
  if rawget(_G, 'jit') then
    jit.off()
    jit.flush()
  end
end
function source.load_settings()
  local settings = Settings.source
  love.graphics.setFont(love.graphics.newFont(settings.font_height))
  -- maximize window to determine maximum allowable dimensions
  love.window.setMode(0, 0)  -- maximize
  Display_width, Display_height, App.screen.flags = love.window.getMode()
  -- set up desired window dimensions
  App.screen.flags.resizable = true
  App.screen.flags.minwidth = math.min(Display_width, 200)
  App.screen.flags.minheight = math.min(Display_height, 200)
  App.screen.width, App.screen.height = settings.width, settings.height
--?   print('setting window from settings:', App.screen.width, App.screen.height)
  love.window.setMode(App.screen.width, App.screen.height, App.screen.flags)
--?   print('loading source position', settings.x, settings.y, settings.displayindex)
  source.set_window_position_from_settings(settings)
  Show_log_browser_side = settings.show_log_browser_side
  local right = App.screen.width - Margin_right
  if Show_log_browser_side then
    right = App.screen.width/2 - Margin_right
  end
  Editor_state = edit.initialize_state(Margin_top, Margin_left, right, settings.font_height, math.floor(settings.font_height*1.3))
  Editor_state.filename = settings.filename
  Editor_state.screen_top1 = settings.screen_top
  Editor_state.cursor1 = settings.cursor
end
function source.set_window_position_from_settings(settings)
  -- setPosition doesn't quite seem to do what is asked of it on Linux.
  love.window.setPosition(settings.x, settings.y-37, settings.displayindex)
end
function source.initialize_default_settings()
  local font_height = 20
  love.graphics.setFont(love.graphics.newFont(font_height))
  local em = App.newText(love.graphics.getFont(), 'm')
  source.initialize_window_geometry(App.width(em))
  Editor_state = edit.initialize_state(Margin_top, Margin_left, App.screen.width-Margin_right)
  Editor_state.font_height = font_height
  Editor_state.line_height = math.floor(font_height*1.3)
  Editor_state.em = em
end
function source.initialize_window_geometry(em_width)
  -- maximize window
  love.window.setMode(0, 0)  -- maximize
  Display_width, Display_height, App.screen.flags = love.window.getMode()
  -- shrink height slightly to account for window decoration
  App.screen.height = Display_height-100
  App.screen.width = 40*em_width
  App.screen.flags.resizable = true
  App.screen.flags.minwidth = math.min(App.screen.width, 200)
  App.screen.flags.minheight = math.min(App.screen.width, 200)
  love.window.setMode(App.screen.width, App.screen.height, App.screen.flags)
  print('initializing source position')
  if Settings == nil then Settings = {} end
  if Settings.source == nil then Settings.source = {} end
  Settings.source.x, Settings.source.y, Settings.source.displayindex = love.window.getPosition()
end
function source.resize(w, h)
--?   print(("Window resized to width: %d and height: %d."):format(w, h))
  App.screen.width, App.screen.height = w, h
  Text.redraw_all(Editor_state)
  Editor_state.selection1 = {}  -- no support for shift drag while we're resizing
  if Show_log_browser_side then
    Editor_state.right = App.screen.width/2 - Margin_right
  else
    Editor_state.right = App.screen.width-Margin_right
  end
  Log_browser_state.left = App.screen.width/2 + Margin_right
  Log_browser_state.right = App.screen.width-Margin_right
  Editor_state.width = Editor_state.right-Editor_state.left
  Text.tweak_screen_top_and_cursor(Editor_state, Editor_state.left, Editor_state.right)
--?   print('end resize')
end
function source.filedropped(file)
  -- first make sure to save edits on any existing file
  if Editor_state.next_save then
    save_to_disk(Editor_state)
  end
  -- clear the slate for the new file
  Editor_state.filename = file:getFilename()
  file:open('r')
  Editor_state.lines = load_from_file(file)
  file:close()
  Text.redraw_all(Editor_state)
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.cursor1 = {line=1, pos=1}
end
-- a copy of source.filedropped when given a filename
function source.switch_to_file(filename)
  -- first make sure to save edits on any existing file
  if Editor_state.next_save then
    save_to_disk(Editor_state)
  end
  -- clear the slate for the new file
  Editor_state.filename = filename
  load_from_disk(Editor_state)
  Text.redraw_all(Editor_state)
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.cursor1 = {line=1, pos=1}
end
function source.draw()
  source.draw_menu_bar()
  edit.draw(Editor_state)
  if Show_log_browser_side then
    -- divider
    App.color(Divider_color)
    love.graphics.rectangle('fill', App.screen.width/2-1,Menu_status_bar_height, 3,App.screen.height)
    --
    log_browser.draw(Log_browser_state)
  end
end
function source.update(dt)
  Cursor_time = Cursor_time + dt
  if App.mouse_x() < Editor_state.right then
    edit.update(Editor_state, dt)
  elseif Show_log_browser_side then
    log_browser.update(Log_browser_state, dt)
  end
end
function source.quit()
  edit.quit(Editor_state)
  log_browser.quit(Log_browser_state)
  -- convert any bifold files here
end
function source.convert_bifold_text(infilename, outfilename)
  local contents = love.filesystem.read(infilename)
  contents = contents:gsub('\u{1e}', ';')
  love.filesystem.write(outfilename, contents)
end
function source.settings()
  if Current_app == 'source' then
--?     print('reading source window position')
    Settings.source.x, Settings.source.y, Settings.source.displayindex = love.window.getPosition()
  end
  local filename = Editor_state.filename
  if filename:sub(1,1) ~= '/' then
    filename = love.filesystem.getWorkingDirectory()..'/'..filename  -- '/' should work even on Windows
  end
--?   print('saving source settings', Settings.source.x, Settings.source.y, Settings.source.displayindex)
  return {
    x=Settings.source.x, y=Settings.source.y, displayindex=Settings.source.displayindex,
    width=App.screen.width, height=App.screen.height,
    font_height=Editor_state.font_height,
    filename=filename,
    screen_top=Editor_state.screen_top1, cursor=Editor_state.cursor1,
    show_log_browser_side=Show_log_browser_side,
    focus=Focus,
  }
end
function source.mouse_pressed(x,y, mouse_button)
  Cursor_time = 0  -- ensure cursor is visible immediately after it moves
--?   print('mouse click', x, y)
--?   print(Editor_state.left, Editor_state.right)
--?   print(Log_browser_state.left, Log_browser_state.right)
  if Editor_state.left <= x and x < Editor_state.right then
--?     print('click on edit side')
    if Focus ~= 'edit' then
      Focus = 'edit'
    end
    edit.mouse_pressed(Editor_state, x,y, mouse_button)
  elseif Show_log_browser_side and Log_browser_state.left <= x and x < Log_browser_state.right then
--?     print('click on log_browser side')
    if Focus ~= 'log_browser' then
      Focus = 'log_browser'
    end
    log_browser.mouse_pressed(Log_browser_state, x,y, mouse_button)
    for _,line_cache in ipairs(Editor_state.line_cache) do line_cache.starty = nil end  -- just in case we scroll
  end
end
function source.mouse_released(x,y, mouse_button)
  Cursor_time = 0  -- ensure cursor is visible immediately after it moves
  if Focus == 'edit' then
    return edit.mouse_released(Editor_state, x,y, mouse_button)
  else
    return log_browser.mouse_released(Log_browser_state, x,y, mouse_button)
  end
end
function source.textinput(t)
  Cursor_time = 0  -- ensure cursor is visible immediately after it moves
  if Focus == 'edit' then
    return edit.textinput(Editor_state, t)
  else
    return log_browser.textinput(Log_browser_state, t)
  end
end
function source.keychord_pressed(chord, key)
  Cursor_time = 0  -- ensure cursor is visible immediately after it moves
--?   print('source keychord')
  if Show_file_navigator then
    keychord_pressed_on_file_navigator(chord, key)
    return
  end
  if chord == 'C-l' then
--?     print('C-l')
    Show_log_browser_side = not Show_log_browser_side
    if Show_log_browser_side then
      App.screen.width = Log_browser_state.right + Margin_right
    else
      App.screen.width = Editor_state.right + Margin_right
    end
--?     print('setting window:', App.screen.width, App.screen.height)
    love.window.setMode(App.screen.width, App.screen.height, App.screen.flags)
--?     print('done setting window')
    -- try to restore position if possible
    -- if the window gets wider the window manager may not respect this
    source.set_window_position_from_settings(Settings.source)
    return
  end
  if chord == 'C-g' then
    Show_file_navigator = true
    File_navigation.index = 1
    return
  end
  if Focus == 'edit' then
    return edit.keychord_pressed(Editor_state, chord, key)
  else
    return log_browser.keychord_pressed(Log_browser_state, chord, key)
  end
end
function source.key_released(key, scancode)
  Cursor_time = 0  -- ensure cursor is visible immediately after it moves
  if Focus == 'edit' then
    return edit.key_released(Editor_state, key, scancode)
  else
    return log_browser.keychord_pressed(Log_browser_state, chordkey, scancode)
  end
end
-- use this sparingly
function to_text(s)
  if Text_cache[s] == nil then
    Text_cache[s] = App.newText(love.graphics.getFont(), s)
  end
  return Text_cache[s]
end