-- 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(data)
  History[Next_history] = data
  Next_history = Next_history+1
  for i=Next_history,#History do
    History[i] = nil
  end
end
function undo_event()
  if Next_history > 1 then
--?     print('moving to history', Next_history-1)
    Next_history = Next_history-1
    local result = History[Next_history]
    return result
  end
end
function redo_event()
  if Next_history <= #History then
--?     print('restoring history', Next_history+1)
    local result = History[Next_history]
    Next_history = Next_history+1
    return result
  end
end
-- Make copies of objects; the rest of the app may mutate them in place, but undo requires immutable histories.
function snapshot_everything()
  -- compare with App.initialize_globals
  local event = {
    screen_top=deepcopy(Screen_top1),
    selection=deepcopy(Selection1),
    cursor=deepcopy(Cursor1),
    current_drawing_mode=Drawing_mode,
    previous_drawing_mode=Previous_drawing_mode,
    zoom=Zoom,
    lines={},
    -- no filename; undo history is cleared when filename changes
  }
  -- deep copy lines without cached stuff like text fragments
  for _,line in ipairs(Lines) do
    if line.mode == 'text' then
      table.insert(event.lines, {mode='text', data=line.data})
    elseif line.mode == 'drawing' then
      local points=deepcopy(line.points)
--?       print('copying', line.points, 'with', #line.points, 'points into', points)
      local shapes=deepcopy(line.shapes)
--?       print('copying', line.shapes, 'with', #line.shapes, 'shapes into', shapes)
      table.insert(event.lines, {mode='drawing', y=line.y, h=line.h, points=points, shapes=shapes, pending={}})
--?       table.insert(event.lines, {mode='drawing', y=line.y, h=line.h, points=deepcopy(line.points), shapes=deepcopy(line.shapes), pending={}})
    else
      print(line.mode)
      assert(false)
    end
  end
  return event
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

require 'undo'

function test_undo_insert_text()
  io.write('\ntest_undo_insert_text')
  App.screen.init{width=120, height=60}
  Lines = load_array{'abc', 'def', 'xyz'}
  Line_width = App.screen.width
  Cursor1 = {line=2, pos=4}
  Screen_top1 = {line=1, pos=1}
  Screen_bottom1 = {}
  Zoom = 1
  -- insert a character
  App.run_after_textinput('g')
  check_eq(Cursor1.line, 2, 'F - test_undo_insert_text/baseline/cursor:line')
  check_eq(Cursor1.pos, 5, 'F - test_undo_insert_text/baseline/cursor:pos')
  check_nil(Selection1.line, 'F - test_undo_insert_text/baseline/selection:line')
  check_nil(Selection1.pos, 'F - test_undo_insert_text/baseline/selection:pos')
  local screen_top_margin = 15  -- pixels
  local line_height = 15  -- pixels
  local y = screen_top_margin
  App.screen.check(y, 'abc', 'F - test_undo_insert_text/baseline/screen:1')
  y = y + line_height
  App.screen.check(y, 'defg', 'F - test_undo_insert_text/baseline/screen:2')
  y = y + line_height
  App.screen.check(y, 'xyz', 'F - test_undo_insert_text/baseline/screen:3')
  -- undo
  App.run_after_keychord('M-z')
  check_eq(Cursor1.line, 2, 'F - test_undo_insert_text/cursor:line')
  check_eq(Cursor1.pos, 4, 'F - test_undo_insert_text/cursor:pos')
  check_nil(Selection1.line, 'F - test_undo_insert_text/selection:line')
  check_nil(Selection1.pos, 'F - test_undo_insert_text/selection:pos')
  y = screen_top_margin
  App.screen.check(y, 'abc', 'F - test_undo_insert_text/screen:1')
  y = y + line_height
  App.screen.check(y, 'def', 'F - test_undo_insert_text/screen:2')
  y = y + 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}
  Lines = load_array{'abc', 'defg', 'xyz'}
  Line_width = App.screen.width
  Cursor1 = {line=2, pos=5}
  Screen_top1 = {line=1, pos=1}
  Screen_bottom1 = {}
  Zoom = 1
  -- delete a character
  App.run_after_keychord('backspace')
  check_eq(Cursor1.line, 2, 'F - test_undo_delete_text/baseline/cursor:line')
  check_eq(Cursor1.pos, 4, 'F - test_undo_delete_text/baseline/cursor:pos')
  check_nil(Selection1.line, 'F - test_undo_delete_text/baseline/selection:line')
  check_nil(Selection1.pos, 'F - test_undo_delete_text/baseline/selection:pos')
  local screen_top_margin = 15  -- pixels
  local line_height = 15  -- pixels
  local y = screen_top_margin
  App.screen.check(y, 'abc', 'F - test_undo_delete_text/baseline/screen:1')
  y = y + line_height
  App.screen.check(y, 'def', 'F - test_undo_delete_text/baseline/screen:2')
  y = y + line_height
  App.screen.check(y, 'xyz', 'F - test_undo_delete_text/baseline/screen:3')
  -- undo
--?   -- after undo, the backspaced key is selected
  App.run_after_keychord('M-z')
  check_eq(Cursor1.line, 2, 'F - test_undo_delete_text/cursor:line')
  check_eq(Cursor1.pos, 5, 'F - test_undo_delete_text/cursor:pos')
  check_nil(Selection1.line, 'F - test_undo_delete_text/selection:line')
  check_nil(Selection1.pos, 'F - test_undo_delete_text/selection:pos')
--?   check_eq(Selection1.line, 2, 'F - test_undo_delete_text/selection:line')
--?   check_eq(Selection1.pos, 4, 'F - test_undo_delete_text/selection:pos')
  y = screen_top_margin
  App.screen.check(y, 'abc', 'F - test_undo_delete_text/screen:1')
  y = y + line_height
  App.screen.check(y, 'defg', 'F - test_undo_delete_text/screen:2')
  y = y + line_height
  App.screen.check(y, 'xyz', 'F - test_undo_delete_text/screen:3')
end

  -- Collect what you did in an event that can be undone.
  local before = snapshot_everything()

  -- finalize undo event
  record_undo_event({before=before, after=snapshot_everything()})

    local before = snapshot_everything()

    record_undo_event({before=before, after=snapshot_everything()})

    local before = snapshot_everything()

    record_undo_event({before=before, after=snapshot_everything()})

    local before = snapshot_everything()

      save_to_disk(Lines, Filename)
      record_undo_event({before=before, after=snapshot_everything()})

    record_undo_event({before=before, after=snapshot_everything()})

    local before = snapshot_everything()

      save_to_disk(Lines, Filename)
      record_undo_event({before=before, after=snapshot_everything()})

    record_undo_event({before=before, after=snapshot_everything()})
  -- undo/redo really belongs in main.lua, but it's here so I can test the
  -- text-specific portions of it
  elseif chord == 'M-z' then
    local event = undo_event()
    if event then
      local src = event.before
      Screen_top1 = deepcopy(src.screen_top)
      Cursor1 = deepcopy(src.cursor)
      Selection1 = deepcopy(src.selection)
      if src.lines then
        Lines = deepcopy(src.lines)
      end
    end
  elseif chord == 'M-y' then
    local event = redo_event()
    if event then
      local src = event.after
      Screen_top1 = deepcopy(src.screen_top)
      Cursor1 = deepcopy(src.cursor)
      Selection1 = deepcopy(src.selection)
      if src.lines then
        Lines = deepcopy(src.lines)
--?         for _,line in ipairs(Lines) do
--?           if line.mode == 'drawing' then
--?             print('restoring', line.points, 'with', #line.points, 'points')
--?             print('restoring', line.shapes, 'with', #line.shapes, 'shapes')
--?           end
--?         end
      end
    end

-- undo
History = {}
Next_history = 1

  App.initialize_globals()  -- in particular, forget all undo history

  Drawing.before = snapshot_everything()

  record_undo_event({before=Drawing.before, after=snapshot_everything()})

* Undo is extremely inefficient in space. While this app is extremely unlikely
  to lose the current state of a file at any moment, undo history is volatile
  and should be considered unstable.