undo.lua

   1 -- undo/redo by managing the sequence of events in the current session
   2 -- based on https://github.com/akkartik/mu1/blob/master/edit/012-editor-undo.mu
   3
   4 -- Incredibly inefficient; we make a copy of lines on every single keystroke.
   5 -- The hope here is that we're either editing small files or just reading large files.
   6 -- TODO: highlight stuff inserted by any undo/redo operation
   7 -- TODO: coalesce multiple similar operations
   8
   9 function record_undo_event(State, data)
  10   State.history[State.next_history] = data
  11   State.next_history = State.next_history+1
  12   for i=State.next_history,#State.history do
  13     State.history[i] = nil
  14   end
  15 end
  16
  17 function undo_event(State)
  18   if State.next_history > 1 then
  19 --?     print('moving to history', State.next_history-1)
  20     State.next_history = State.next_history-1
  21     local result = State.history[State.next_history]
  22     return result
  23   end
  24 end
  25
  26 function redo_event(State)
  27   if State.next_history <= #State.history then
  28 --?     print('restoring history', State.next_history+1)
  29     local result = State.history[State.next_history]
  30     State.next_history = State.next_history+1
  31     return result
  32   end
  33 end
  34
  35 -- Copy all relevant global state.
  36 -- Make copies of objects; the rest of the app may mutate them in place, but undo requires immutable histories.
  37 function snapshot(State, s,e)
  38   -- Snapshot everything by default, but subset if requested.
  39   assert(s)
  40   if e == nil then
  41     e = s
  42   end
  43   assert(#State.lines > 0)
  44   if s < 1 then s = 1 end
  45   if s > #State.lines then s = #State.lines end
  46   if e < 1 then e = 1 end
  47   if e > #State.lines then e = #State.lines end
  48   -- compare with App.initialize_globals
  49   local event = {
  50     screen_top=deepcopy(State.screen_top1),
  51     selection=deepcopy(State.selection1),
  52     cursor=deepcopy(State.cursor1),
  53     current_drawing_mode=Drawing_mode,
  54     previous_drawing_mode=State.previous_drawing_mode,
  55     lines={},
  56     start_line=s,
  57     end_line=e,
  58     -- no filename; undo history is cleared when filename changes
  59   }
  60   -- deep copy lines without cached stuff like text fragments
  61   for i=s,e do
  62     local line = State.lines[i]
  63     if line.mode == 'text' then
  64       table.insert(event.lines, {mode='text', data=line.data})  -- I've forgotten: should we deepcopy(line.data)?
  65     elseif line.mode == 'drawing' then
  66       table.insert(event.lines, {mode='drawing', h=line.h, points=deepcopy(line.points), shapes=deepcopy(line.shapes), pending={}})
  67     else
  68       print(line.mode)
  69       assert(false)
  70     end
  71   end
  72   return event
  73 end
  74
  75 function patch(lines, from, to)
  76 --?   if #from.lines == 1 and #to.lines == 1 then
  77 --?     assert(from.start_line == from.end_line)
  78 --?     assert(to.start_line == to.end_line)
  79 --?     assert(from.start_line == to.start_line)
  80 --?     lines[from.start_line] = to.lines[1]
  81 --?     return
  82 --?   end
  83   assert(from.start_line == to.start_line)
  84   for i=from.end_line,from.start_line,-1 do
  85     table.remove(lines, i)
  86   end
  87   assert(#to.lines == to.end_line-to.start_line+1)
  88   for i=1,#to.lines do
  89     table.insert(lines, to.start_line+i-1, to.lines[i])
  90   end
  91 end
  92
  93 function patch_placeholders(line_cache, from, to)
  94   assert(from.start_line == to.start_line)
  95   for i=from.end_line,from.start_line,-1 do
  96     table.remove(line_cache, i)
  97   end
  98   assert(#to.lines == to.end_line-to.start_line+1)
  99   for i=1,#to.lines do
 100     table.insert(line_cache, to.start_line+i-1, {})
 101   end
 102 end
 103
 104 -- https://stackoverflow.com/questions/640642/how-do-you-copy-a-lua-table-by-value/26367080#26367080
 105 function deepcopy(obj, seen)
 106   if type(obj) ~= 'table' then return obj end
 107   if seen and seen[obj] then return seen[obj] end
 108   local s = seen or {}
 109   local result = setmetatable({}, getmetatable(obj))
 110   s[obj] = result
 111   for k,v in pairs(obj) do
 112     result[deepcopy(k, s)] = deepcopy(v, s)
 113   end
 114   return result
 115 end
 116
 117 function minmax(a, b)
 118   return math.min(a,b), math.max(a,b)
 119 end