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 -- makes a copy of lines on every single keystroke; will be inefficient with really long lines.
   5 -- TODO: highlight stuff inserted by any undo/redo operation
   6 -- TODO: coalesce multiple similar operations
   7
   8 function record_undo_event(State, data)
   9   State.history[State.next_history] = data
  10   State.next_history = State.next_history+1
  11   for i=State.next_history,#State.history do
  12     State.history[i] = nil
  13   end
  14 end
  15
  16 function undo_event(State)
  17   if State.next_history > 1 then
  18 --?     print('moving to history', State.next_history-1)
  19     State.next_history = State.next_history-1
  20     local result = State.history[State.next_history]
  21     return result
  22   end
  23 end
  24
  25 function redo_event(State)
  26   if State.next_history <= #State.history then
  27 --?     print('restoring history', State.next_history+1)
  28     local result = State.history[State.next_history]
  29     State.next_history = State.next_history+1
  30     return result
  31   end
  32 end
  33
  34 -- Copy all relevant global state.
  35 -- Make copies of objects; the rest of the app may mutate them in place, but undo requires immutable histories.
  36 function snapshot(State, s,e)
  37   -- Snapshot everything by default, but subset if requested.
  38   assert(s, 'failed to snapshot operation for undo history')
  39   if e == nil then
  40     e = s
  41   end
  42   assert(#State.lines > 0, 'failed to snapshot operation for undo history')
  43   if s < 1 then s = 1 end
  44   if s > #State.lines then s = #State.lines end
  45   if e < 1 then e = 1 end
  46   if e > #State.lines then e = #State.lines end
  47   -- compare with App.initialize_globals
  48   local event = {
  49     screen_top=deepcopy(State.screen_top1),
  50     selection=deepcopy(State.selection1),
  51     cursor=deepcopy(State.cursor1),
  52     lines={},
  53     start_line=s,
  54     end_line=e,
  55     -- no filename; undo history is cleared when filename changes
  56   }
  57   for i=s,e do
  58     table.insert(event.lines, deepcopy(State.lines[i]))
  59   end
  60   return event
  61 end
  62
  63 function patch(lines, from, to)
  64 --?   if #from.lines == 1 and #to.lines == 1 then
  65 --?     assert(from.start_line == from.end_line)
  66 --?     assert(to.start_line == to.end_line)
  67 --?     assert(from.start_line == to.start_line)
  68 --?     lines[from.start_line] = to.lines[1]
  69 --?     return
  70 --?   end
  71   assert(from.start_line == to.start_line, 'failed to patch undo operation')
  72   for i=from.end_line,from.start_line,-1 do
  73     table.remove(lines, i)
  74   end
  75   assert(#to.lines == to.end_line-to.start_line+1, 'failed to patch undo operation')
  76   for i=1,#to.lines do
  77     table.insert(lines, to.start_line+i-1, to.lines[i])
  78   end
  79 end
  80
  81 -- https://stackoverflow.com/questions/640642/how-do-you-copy-a-lua-table-by-value/26367080#26367080
  82 function deepcopy(obj, seen)
  83   if type(obj) ~= 'table' then return obj end
  84   if seen and seen[obj] then return seen[obj] end
  85   local s = seen or {}
  86   local result = setmetatable({}, getmetatable(obj))
  87   s[obj] = result
  88   for k,v in pairs(obj) do
  89     result[deepcopy(k, s)] = deepcopy(v, s)
  90   end
  91   return result
  92 end
  93
  94 function minmax(a, b)
  95   return math.min(a,b), math.max(a,b)
  96 end