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, 'failed to snapshot operation for undo history')
  40   if e == nil then
  41     e = s
  42   end
  43   assert(#State.lines > 0, 'failed to snapshot operation for undo history')
  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     lines={},
  54     start_line=s,
  55     end_line=e,
  56     -- no filename; undo history is cleared when filename changes
  57   }
  58   -- deep copy lines without cached stuff like text fragments
  59   for i=s,e do
  60     local line = State.lines[i]
  61     table.insert(event.lines, {data=line.data})  -- I've forgotten: should we deepcopy(line.data)?
  62   end
  63   return event
  64 end
  65
  66 function patch(lines, from, to)
  67 --?   if #from.lines == 1 and #to.lines == 1 then
  68 --?     assert(from.start_line == from.end_line)
  69 --?     assert(to.start_line == to.end_line)
  70 --?     assert(from.start_line == to.start_line)
  71 --?     lines[from.start_line] = to.lines[1]
  72 --?     return
  73 --?   end
  74   assert(from.start_line == to.start_line, 'failed to patch undo operation')
  75   for i=from.end_line,from.start_line,-1 do
  76     table.remove(lines, i)
  77   end
  78   assert(#to.lines == to.end_line-to.start_line+1, 'failed to patch undo operation')
  79   for i=1,#to.lines do
  80     table.insert(lines, to.start_line+i-1, to.lines[i])
  81   end
  82 end
  83
  84 function patch_placeholders(line_cache, from, to)
  85   assert(from.start_line == to.start_line, 'failed to patch undo operation')
  86   for i=from.end_line,from.start_line,-1 do
  87     table.remove(line_cache, i)
  88   end
  89   assert(#to.lines == to.end_line-to.start_line+1, 'failed to patch undo operation')
  90   for i=1,#to.lines do
  91     table.insert(line_cache, to.start_line+i-1, {})
  92   end
  93 end
  94
  95 -- https://stackoverflow.com/questions/640642/how-do-you-copy-a-lua-table-by-value/26367080#26367080
  96 function deepcopy(obj, seen)
  97   if type(obj) ~= 'table' then return obj end
  98   if seen and seen[obj] then return seen[obj] end
  99   local s = seen or {}
 100   local result = setmetatable({}, getmetatable(obj))
 101   s[obj] = result
 102   for k,v in pairs(obj) do
 103     result[deepcopy(k, s)] = deepcopy(v, s)
 104   end
 105   return result
 106 end
 107
 108 function minmax(a, b)
 109   return math.min(a,b), math.max(a,b)
 110 end