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
-- result: pos, index of screen line
    end
  end
end
  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')
  assert(State.cursor1.pos, 'cursor has no pos')
--?   print('down', State.cursor1.line, State.cursor1.pos, State.screen_top1.line, State.screen_top1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)
  assert(State.lines[State.cursor1.line].mode == 'text', 'line is not text')
function Text.down(State)
  end
end
    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)
--?     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)
    State.cursor1.pos = new_screen_line_starting_pos + Text.nearest_cursor_pos(State.font, s, State.cursor_x, State.left) - 1
    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)
  else
    -- move down one screen line in current line
    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
        }
--?         print(State.cursor1.pos)
        break
      end
          pos = Text.nearest_cursor_pos(State.font, State.lines[new_cursor_line].data, State.cursor_x, State.left),
    local new_cursor_line = State.cursor1.line
    while new_cursor_line < #State.lines do
      new_cursor_line = new_cursor_line+1
      if State.lines[new_cursor_line].mode == 'text' then
        State.cursor1 = {
          line = new_cursor_line,
end
function ends_with(s, suffix)
  if #s < #suffix then
    return false
  end
  for i=0,#suffix-1 do
    if s:sub(#s-i,#s-i) ~= suffix:sub(#suffix-i,#suffix-i) then
      return false
    end
  end
  return true
end
function starts_with(s, prefix)
  if #s < #prefix then
    return false
  end
  for i=1,#prefix do
    if s:sub(i,i) ~= prefix:sub(i,i) then
      return false
    end
  end
  return true
end
end
function trim(s)
  return s:gsub('^%s+', ''):gsub('%s+$', '')
end
function ltrim(s)
  return s:gsub('^%s+', '')
end
function rtrim(s)
  return s:gsub('%s+$', '')
  State.line_cache[line_index].link_offsets = nil
  State.line_cache[line_index].screen_line_starting_pos = nil
end
function Text.clear_screen_line_cache(State, line_index)
  State.line_cache = {}
  for i=1,#State.lines do
    State.line_cache[i] = {}
  end
  -- Perform some early sanity checking here, in hopes that we correctly call
  -- this whenever we change editor state.
  if State.right <= State.left then
    assert(false, ('Right margin %d must be to the right of the left margin %d'):format(State.right, State.left))
  end
end
function Text.redraw_all(State)
--?   print('clearing fragments')
  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)
  edit.draw(State)
    end
  end
end
-- slightly expensive since it redraws the screen
function Text.cursor_out_of_screen(State)
      State.cursor1 = {
          line=State.screen_bottom1.line,
          pos=Text.to_pos_on_line(State, State.screen_bottom1.line, State.right-5, App.screen.height-5),
      }
  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')
    return {line=loc2.line-1, screen_line=#State.line_cache[loc2.line-1].screen_line_starting_pos, screen_pos=1}
    Text.populate_screen_line_starting_pos(State, loc2.line-1)
    local l = State.lines[loc2.line-1]
  else
  elseif State.lines[loc2.line-1].mode == 'drawing' then
    return {line=loc2.line-1, screen_line=1, screen_pos=1}
  if loc2.screen_line > 1 then
    return {line=loc2.line, screen_line=loc2.screen_line-1, screen_pos=1}
  elseif loc2.line == 1 then
    return loc2
  return result
end
function Text.previous_screen_line(State, loc2)
  end
    assert(false, ('Text.offset(%d) called on a string of length %d (byte size %d); this is likely a failure to handle utf8\n\n^%s$\n'):format(pos1, utf8.len(s), #s, s))
end
function Text.offset(s, pos1)
  if pos1 == 1 then return 1 end
  local result = utf8.offset(s, pos1)
  if result == nil then
  return a.pos <= b.pos
    return false
  end
  if a.line > b.line then
    return true
  end
  return a.pos < b.pos
end
function Text.le1(a, b)
  if a.line < b.line then
end
function Text.lt1(a, b)
  if a.line < b.line then
    return true
  end
  if a.line > b.line then
    return false
  end
function Text.eq1(a, b)
  return a.line == b.line and a.pos == b.pos
  local result = {line=loc2.line, pos=loc2.screen_pos}
  if loc2.screen_line > 1 then
    result.pos = State.line_cache[loc2.line].screen_line_starting_pos[loc2.screen_line] + loc2.screen_pos - 1
  end
  return result
end
  return result
end
function Text.to1(State, loc2)
  assert(result.screen_pos, 'failed to convert schema-1 coordinate to schema-2')
  local result = {line=loc1.line}
  local line_cache = State.line_cache[loc1.line]
  Text.populate_screen_line_starting_pos(State, loc1.line)
  for i=#line_cache.screen_line_starting_pos,1,-1 do
    local spos = line_cache.screen_line_starting_pos[i]
    if spos <= loc1.pos then
      result.screen_line = i
      result.screen_pos = loc1.pos - spos + 1
      break
    end
  end
  end
  if State.lines[loc1.line].mode == 'drawing' then
    return {line=loc1.line, screen_line=1, screen_pos=1}
end
function Text.to2(State, loc1)
  return font:getWidth(s_before)
  local offset = Text.offset(s, pos)
  local s_before = s:sub(1, offset-1)
function Text.x(font, s, pos)
end
  return font:getWidth(s_before)
  local s_before = s:sub(1, offset-1)
--?   print('^'..s_before..'$')
  local len = utf8.len(s)
  local offset = Text.offset(s, math.min(pos+1, len+1))
function Text.x_after(font, s, pos)
end
  assert(false, 'failed to map x pixel to pos')
--?     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
    local currxmin = Text.x_after(font, line, curr+1)
    local currxmax = Text.x_after(font, line, curr+2)
  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 max_x = Text.x_after(font, line, len)
--?   print('', '-- nearest_pos_less_than', line, x)
  local len = utf8.len(line)
function Text.nearest_pos_less_than(font, line, x)
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
  assert(false, 'failed to map x pixel to pos')
--?     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
    local currxmin = left+Text.x(font, line, curr)
    local currxmax = left+Text.x(font, line, curr+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 max_x = left+Text.x(font, line, len+1)
  if x < left then
    return 1
  end
  local len = utf8.len(line)
function Text.nearest_cursor_pos(font, line, x, left)
      return i
    end
  end
end
-- convert x pixel coordinate to pos
-- oblivious to wrapping
-- result: 1 to len+1
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 State.font:getWidth(screen_line)
  end
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)
  assert(false, 'failed to map y pixel to line')
    end
    y = nexty
  end
--?       print('return', mx, Text.nearest_cursor_pos(State.font, s, mx, State.left), '=>', screen_line_starting_pos + Text.nearest_cursor_pos(State.font, s, mx, State.left) - 1)
      return screen_line_starting_pos + Text.nearest_cursor_pos(State.font, s, mx, State.left) - 1
      local s = string.sub(line.data, screen_line_starting_byte_offset)
      end
        return line_cache.screen_line_starting_pos[screen_line_index+1]-1
--?         print('past end of non-final line; return')
      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
    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.)
  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))
  -- duplicate some logic from Text.draw
  local y = line_cache.starty
  assert(my >= line_cache.starty, 'failed to map y pixel to line')
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]
end
-- convert mx,my in pixels to schema-1 coordinates
  Text.populate_screen_line_starting_pos(State, line_index)
  return y < line_cache.starty + State.line_height*(#line_cache.screen_line_starting_pos - Text.screen_line_index(line_cache.screen_line_starting_pos, line_cache.startpos) + 1)
  Text.redraw_all(State)  -- if we're scrolling, reclaim all fragments to avoid memory leaks
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
--?   print('snap =>', State.screen_top1.line, State.screen_top1.pos, State.cursor1.line, State.cursor1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)
    end
    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)
      -- We currently can't draw partial drawings, so either skip it entirely
      -- or not at all.
      local h = Drawing_padding_height + Drawing.pixels(State.lines[top2.line-1].h, State.width)
      if y - h < State.top then
        break
      end
--?       print('skipping drawing of height', h)
      y = y - h
      assert(top2.line > 1, 'tried to snap cursor to buttom of screen but failed')
      assert(State.lines[top2.line-1].mode == 'drawing', "expected a drawing but it's not")
    if top2.screen_line > 1 or State.lines[top2.line-1].mode == 'text' then
      local h = State.line_height
      if y - h < State.top then
        break
      end
      y = y - h
    else
    if top2.line == 1 and top2.screen_line == 1 then break end
--?     print(y, 'top2:', top2.line, top2.screen_line, top2.screen_pos)
--?   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
  top2.screen_pos = 1  -- start of screen line
--?   print('snap', State.screen_top1.line, State.screen_top1.pos, State.cursor1.line, State.cursor1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)
  -- slide to start of screen line
--?   print('to2: =>', top2.line, top2.screen_line, top2.screen_pos)
  local top2 = Text.to2(State, State.cursor1)
--?   print('to2:', State.cursor1.line, State.cursor1.pos)
--?     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)
    table.insert(State.lines, {mode='text', data=''})
    table.insert(State.line_cache, {})
  end
--?   print(y, App.screen.height, App.screen.height-State.line_height)
  if y > App.screen.height - State.line_height then
    assert(State.cursor1.line == #State.lines+1, 'tried to ensure bottom line of file is text, but failed')
  end
  -- hack: insert a text line at bottom of file if necessary
  if State.cursor1.line > #State.lines then
  end
  if State.cursor1.pos == nil then
    State.cursor1.pos = 1
  local y = State.top
  while State.cursor1.line <= #State.lines do
    if State.lines[State.cursor1.line].mode == 'text' then
      break
    end
--?     print('cursor skips', State.cursor1.line)
    y = y + Drawing_padding_height + Drawing.pixels(State.lines[State.cursor1.line].h, State.width)
    State.cursor1.line = State.cursor1.line + 1
function Text.cursor_at_final_screen_line(State)
  Text.populate_screen_line_starting_pos(State, State.cursor1.line)
  local screen_lines = State.line_cache[State.cursor1.line].screen_line_starting_pos
--?   print(screen_lines[#screen_lines], State.cursor1.pos)
  return screen_lines[#screen_lines] <= State.cursor1.pos
end
function Text.move_cursor_down_to_next_text_line_while_scrolling_again_if_necessary(State)
end
  assert(false, ('invalid pos %d'):format(loc1.pos))
function Text.pos_at_end_of_screen_line(State, loc1)
  Text.populate_screen_line_starting_pos(State, loc1.line)
  local line_cache = State.line_cache[loc1.line]
  local most_recent_final_pos = utf8.len(State.lines[loc1.line].data)+1
  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 most_recent_final_pos
    end
    most_recent_final_pos = spos-1
  end
end
  assert(false, ('invalid pos %d'):format(loc1.pos))
  end
    end
    local new_cursor_line = State.cursor1.line
    while new_cursor_line <= #State.lines-1 do
      new_cursor_line = new_cursor_line+1
      if State.lines[new_cursor_line].mode == 'text' then
        State.cursor1 = {line=new_cursor_line, pos=1}
        break
      end
  else
  if State.cursor1.pos <= utf8.len(State.lines[State.cursor1.line].data) then
    State.cursor1.pos = State.cursor1.pos+1
  assert(State.lines[State.cursor1.line].mode == 'text', 'line is not text')
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)
  end
end
    State.screen_top1 = {
      line=State.cursor1.line,
      pos=Text.pos_at_start_of_screen_line(State, State.cursor1),
    }
    Text.redraw_all(State)  -- if we're scrolling, reclaim all fragments to avoid memory leaks
  end
  if Text.lt1(State.cursor1, State.screen_top1) then
    local new_cursor_line = State.cursor1.line
    while new_cursor_line > 1 do
      new_cursor_line = new_cursor_line-1
      if State.lines[new_cursor_line].mode == 'text' then
        State.cursor1 = {
          line = new_cursor_line,
          pos = utf8.len(State.lines[new_cursor_line].data) + 1,
        }
        break
      end
    end
  if State.cursor1.pos > 1 then
    State.cursor1.pos = State.cursor1.pos-1
  else
  assert(State.lines[State.cursor1.line].mode == 'text', 'line is not text')
  local curr = s:sub(start_offset, end_offset-1)
  return curr:match(pat)
end
function Text.left(State)
  assert(end_offset > start_offset, ('end_offset %d not > start_offset %d'):format(end_offset, start_offset))
  local end_offset = Text.offset(s, pos+1)
  end
end
function Text.match(s, pos, pat)
  local start_offset = Text.offset(s, pos)
  if Text.cursor_out_of_screen(State) then
    Text.snap_cursor_to_bottom_of_screen(State)
  end
    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)
  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
  while true do
function Text.word_right(State)
  -- skip some whitespace
  end
end
    if Text.match(State.lines[State.cursor1.line].data, State.cursor1.pos-1, '%s') then
      break
    end
    assert(State.cursor1.pos > 1, 'bumped up against start of line')
    if State.cursor1.pos == 1 then
      break
    end
    Text.left(State)
  while true do
  -- skip some non-whitespace
  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
  -- skip some whitespace
  if Text.cursor_out_of_screen(State) then
    Text.snap_cursor_to_bottom_of_screen(State)
  end
end
function Text.word_left(State)
  State.cursor1.pos = utf8.len(State.lines[State.cursor1.line].data) + 1
  end
end
function Text.end_of_line(State)
  if Text.lt1(State.cursor1, State.screen_top1) then
    State.screen_top1 = {line=State.cursor1.line, pos=State.cursor1.pos}  -- copy
  State.cursor1.pos = 1
    State.screen_top1 = {
      line=State.cursor1.line,
      pos=Text.pos_at_start_of_screen_line(State, State.cursor1),
    }
    Text.redraw_all(State)  -- if we're scrolling, reclaim all fragments to avoid memory leaks
--?     print('cursor pos is now '..tostring(State.cursor1.pos))
  end
  if Text.lt1(State.cursor1, State.screen_top1) then
    State.cursor1.pos = new_screen_line_starting_pos + Text.nearest_cursor_pos(State.font, s, State.cursor_x, State.left) - 1

    State.cursor1.pos = new_screen_line_starting_pos + Text.nearest_cursor_pos(State.font, 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
    State.screen_top1 = {
      line=State.cursor1.line,
      pos=Text.pos_at_start_of_screen_line(State, State.cursor1),
    }
    Text.redraw_all(State)  -- if we're scrolling, reclaim all fragments to avoid memory leaks
  end
end
function Text.down(State)
  assert(State.lines[State.cursor1.line].mode == 'text', 'line is not text')
--?   print('down', State.cursor1.line, State.cursor1.pos, State.screen_top1.line, State.screen_top1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)
  assert(State.cursor1.pos, 'cursor has no 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')
    local new_cursor_line = State.cursor1.line
    while new_cursor_line < #State.lines do
      new_cursor_line = new_cursor_line+1
      if State.lines[new_cursor_line].mode == 'text' then
        State.cursor1 = {
          line = new_cursor_line,
          pos = Text.nearest_cursor_pos(State.font, State.lines[new_cursor_line].data, State.cursor_x, State.left),
        }
--?         print(State.cursor1.pos)
        break
      end
    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
  else
    -- move down one screen line 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(State.font, 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
  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)
  State.cursor1.pos = 1
  if Text.lt1(State.cursor1, State.screen_top1) then
    State.screen_top1 = {line=State.cursor1.line, pos=State.cursor1.pos}  -- copy
  end
end
function Text.end_of_line(State)
  State.cursor1.pos = utf8.len(State.lines[State.cursor1.line].data) + 1
  if Text.cursor_out_of_screen(State) then
    Text.snap_cursor_to_bottom_of_screen(State)
  end
end
function Text.word_left(State)
  -- skip some whitespace
  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
  -- skip some non-whitespace
  while true do
    Text.left(State)
    if State.cursor1.pos == 1 then
      break
    end
    assert(State.cursor1.pos > 1, 'bumped up against start of line')
    if Text.match(State.lines[State.cursor1.line].data, State.cursor1.pos-1, '%s') then
      break
    end
  end
end
function Text.word_right(State)
  -- skip some whitespace
  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
  while true do
    Text.right_without_scroll(State)
    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
  end
  if Text.cursor_out_of_screen(State) then
    Text.snap_cursor_to_bottom_of_screen(State)
  end
end
function Text.match(s, pos, pat)
  local start_offset = Text.offset(s, pos)
  local end_offset = Text.offset(s, pos+1)
  assert(end_offset > start_offset, ('end_offset %d not > start_offset %d'):format(end_offset, start_offset))
  local curr = s:sub(start_offset, end_offset-1)
  return curr:match(pat)
end
function Text.left(State)
  assert(State.lines[State.cursor1.line].mode == 'text', 'line is not text')
  if State.cursor1.pos > 1 then
    State.cursor1.pos = State.cursor1.pos-1
  else
    local new_cursor_line = State.cursor1.line
    while new_cursor_line > 1 do
      new_cursor_line = new_cursor_line-1
      if State.lines[new_cursor_line].mode == 'text' then
        State.cursor1 = {
          line = new_cursor_line,
          pos = utf8.len(State.lines[new_cursor_line].data) + 1,
        }
        break
      end
    end
  end
  if Text.lt1(State.cursor1, State.screen_top1) then
    State.screen_top1 = {
      line=State.cursor1.line,
      pos=Text.pos_at_start_of_screen_line(State, State.cursor1),
    }
    Text.redraw_all(State)  -- if we're scrolling, reclaim all fragments to avoid memory leaks
  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)
  assert(State.lines[State.cursor1.line].mode == 'text', 'line is not text')
  if State.cursor1.pos <= utf8.len(State.lines[State.cursor1.line].data) then
    State.cursor1.pos = State.cursor1.pos+1
  else
    local new_cursor_line = State.cursor1.line
    while new_cursor_line <= #State.lines-1 do
      new_cursor_line = new_cursor_line+1
      if State.lines[new_cursor_line].mode == 'text' then
        State.cursor1 = {line=new_cursor_line, pos=1}
        break
      end
    end
  end
end
-- result: pos, index of screen line
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, ('invalid pos %d'):format(loc1.pos))
end
function Text.pos_at_end_of_screen_line(State, loc1)
  Text.populate_screen_line_starting_pos(State, loc1.line)
  local line_cache = State.line_cache[loc1.line]
  local most_recent_final_pos = utf8.len(State.lines[loc1.line].data)+1
  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 most_recent_final_pos
    end
    most_recent_final_pos = spos-1
  end
  assert(false, ('invalid pos %d'):format(loc1.pos))
end
function Text.cursor_at_final_screen_line(State)
  Text.populate_screen_line_starting_pos(State, State.cursor1.line)
  local screen_lines = State.line_cache[State.cursor1.line].screen_line_starting_pos
--?   print(screen_lines[#screen_lines], State.cursor1.pos)
  return screen_lines[#screen_lines] <= State.cursor1.pos
end
function Text.move_cursor_down_to_next_text_line_while_scrolling_again_if_necessary(State)
  local y = State.top
  while State.cursor1.line <= #State.lines do
    if State.lines[State.cursor1.line].mode == 'text' then
      break
    end
--?     print('cursor skips', State.cursor1.line)
    y = y + Drawing_padding_height + Drawing.pixels(State.lines[State.cursor1.line].h, State.width)
    State.cursor1.line = State.cursor1.line + 1
  end
  if State.cursor1.pos == nil then
    State.cursor1.pos = 1
  end
  -- hack: insert a text line at bottom of file if necessary
  if State.cursor1.line > #State.lines then
    assert(State.cursor1.line == #State.lines+1, 'tried to ensure bottom line of file is text, but failed')
    table.insert(State.lines, {mode='text', data=''})
    table.insert(State.line_cache, {})
  end
--?   print(y, App.screen.height, App.screen.height-State.line_height)
  if y > 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)
  local top2 = Text.to2(State, State.cursor1)
--?   print('to2: =>', top2.line, top2.screen_line, top2.screen_pos)
  -- slide to start of screen line
  top2.screen_pos = 1  -- start of screen line
--?   print('snap', State.screen_top1.line, State.screen_top1.pos, State.cursor1.line, State.cursor1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)
--?   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:', top2.line, top2.screen_line, top2.screen_pos)
    if top2.line == 1 and top2.screen_line == 1 then break end
    if top2.screen_line > 1 or State.lines[top2.line-1].mode == 'text' then
      local h = State.line_height
      if y - h < State.top then
        break
      end
      y = y - h
    else
      assert(top2.line > 1, 'tried to snap cursor to buttom of screen but failed')
      assert(State.lines[top2.line-1].mode == 'drawing', "expected a drawing but it's not")
      -- We currently can't draw partial drawings, so either skip it entirely
      -- or not at all.
      local h = Drawing_padding_height + Drawing.pixels(State.lines[top2.line-1].h, State.width)
      if y - h < State.top then
        break
      end
--?       print('skipping drawing of height', h)
      y = y - h
    end
    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.cursor1.line, State.cursor1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)
  Text.redraw_all(State)  -- if we're scrolling, reclaim all fragments to avoid memory leaks
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
  Text.populate_screen_line_starting_pos(State, line_index)
  return y < line_cache.starty + State.line_height*(#line_cache.screen_line_starting_pos - Text.screen_line_index(line_cache.screen_line_starting_pos, line_cache.startpos) + 1)
end
-- convert mx,my in pixels to schema-1 coordinates
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, 'failed to map y pixel to line')
  -- duplicate some logic from Text.draw
  local y = line_cache.starty
  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(State.font, s, mx, State.left), '=>', screen_line_starting_pos + Text.nearest_cursor_pos(State.font, s, mx, State.left) - 1)
      return screen_line_starting_pos + Text.nearest_cursor_pos(State.font, s, mx, State.left) - 1
    end
    y = nexty
  end
  assert(false, 'failed to map y pixel to line')
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
  return State.font:getWidth(screen_line)
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
-- convert x pixel coordinate to pos
-- oblivious to wrapping
-- result: 1 to len+1
function Text.nearest_cursor_pos(font, line, x, left)
  if x < left then
    return 1
  end
  local len = utf8.len(line)
  local max_x = left+Text.x(font, 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..'$', leftpos, rightpos)
    if leftpos == rightpos then
      return leftpos
    end
    local curr = math.floor((leftpos+rightpos)/2)
    local currxmin = left+Text.x(font, line, curr)
    local currxmax = left+Text.x(font, line, curr+1)
--?     print('nearest', x, leftpos, rightpos, curr, currxmin, currxmax)
    if currxmin <= x and x < currxmax then
      if x-currxmin < currxmax-x then
        return curr
      else
        return curr+1
      end
    end
    if leftpos >= rightpos-1 then
      return rightpos
    end
    if currxmin > x then
      rightpos = curr
    else
      leftpos = curr
    end
  end
  assert(false, 'failed to map x pixel to pos')
end
-- return the nearest index of line (in utf8 code points) which lies entirely
-- within x pixels of the left margin
-- result: 0 to len+1
function Text.nearest_pos_less_than(font, line, x)
--?   print('', '-- nearest_pos_less_than', line, x)
  local len = utf8.len(line)
  local max_x = Text.x_after(font, line, len)
  if x > max_x then
    return len+1
  end
  local left, right = 0, len+1
  while true do
    local curr = math.floor((left+right)/2)
    local currxmin = Text.x_after(font, line, curr+1)
    local currxmax = Text.x_after(font, line, curr+2)
--?     print('', x, left, right, curr, currxmin, currxmax)
    if currxmin <= x and x < currxmax then
      return curr
    end
    if left >= right-1 then
      return left
    end
    if currxmin > x then
      right = curr
    else
      left = curr
    end
  end
  assert(false, 'failed to map x pixel to pos')
end
function Text.x_after(font, s, pos)
  local len = utf8.len(s)
  local offset = Text.offset(s, math.min(pos+1, len+1))
  local s_before = s:sub(1, offset-1)
--?   print('^'..s_before..'$')
  return font:getWidth(s_before)
end
function Text.x(font, s, pos)
  local offset = Text.offset(s, pos)
  local s_before = s:sub(1, offset-1)
  return font:getWidth(s_before)
end
function Text.to2(State, loc1)
  if State.lines[loc1.line].mode == 'drawing' then
    return {line=loc1.line, screen_line=1, screen_pos=1}
  end
  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, 'failed to convert schema-1 coordinate to schema-2')
  return result
end
function Text.to1(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.eq1(a, b)
  return a.line == b.line and a.pos == b.pos
end
function Text.lt1(a, b)
  if a.line < b.line then
    return true
  end
  if a.line > b.line then
    return false
  end
  return a.pos < b.pos
end
function Text.le1(a, b)
  if a.line < b.line then
    return true
  end
  if a.line > b.line then
    return false
  end
  return a.pos <= b.pos
end
function Text.offset(s, pos1)
  if pos1 == 1 then return 1 end
  local result = utf8.offset(s, pos1)
  if result == nil then
    assert(false, ('Text.offset(%d) called on a string of length %d (byte size %d); this is likely a failure to handle utf8\n\n^%s$\n'):format(pos1, utf8.len(s), #s, s))
  end
  return result
end
function Text.previous_screen_line(State, loc2)
  if loc2.screen_line > 1 then
    return {line=loc2.line, screen_line=loc2.screen_line-1, screen_pos=1}
  elseif loc2.line == 1 then
    return loc2
  elseif State.lines[loc2.line-1].mode == 'drawing' then
    return {line=loc2.line-1, screen_line=1, screen_pos=1}
  else
    local l = State.lines[loc2.line-1]
    Text.populate_screen_line_starting_pos(State, loc2.line-1)
    return {line=loc2.line-1, screen_line=#State.line_cache[loc2.line-1].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')
      State.cursor1 = {
          line=State.screen_bottom1.line,
          pos=Text.to_pos_on_line(State, State.screen_bottom1.line, State.right-5, App.screen.height-5),
      }
    end
  end
end
-- slightly expensive since it redraws the screen
function Text.cursor_out_of_screen(State)
  edit.draw(State)
  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')
  -- Perform some early sanity checking here, in hopes that we correctly call
  -- this whenever we change editor state.
  if State.right <= State.left then
    assert(false, ('Right margin %d must be to the right of the left margin %d'):format(State.right, State.left))
  end
  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].screen_line_starting_pos = nil
  State.line_cache[line_index].link_offsets = 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 starts_with(s, prefix)
  if #s < #prefix then
    return false
  end
  for i=1,#prefix do
    if s:sub(i,i) ~= prefix:sub(i,i) then
      return false
    end
  end
  return true
end
function ends_with(s, suffix)
  if #s < #suffix then
    return false
  end
  for i=0,#suffix-1 do
    if s:sub(#s-i,#s-i) ~= suffix:sub(#suffix-i,#suffix-i) then
      return false
    end
  end
  return true
end