Basic implementation of undo/redo

It's not great, as the granularity is too low. But it's a good first
step. It only works in the RawEditor so far.

lib/editors/bottom_bar.dart

@@ -24,6 +24,9 @@ class EditorBottomBar extends StatelessWidget {
   final Func0<void> onZenModeChanged;
   final bool metaDataEditable;
 
+  final bool undoAllowed;
+  final bool redoAllowed;
+
   final Func0<void> onUndoSelected;
   final Func0<void> onRedoSelected;
 
@@ -37,6 +40,8 @@ class EditorBottomBar extends StatelessWidget {
     @required this.metaDataEditable,
     @required this.onUndoSelected,
     @required this.onRedoSelected,
+    @required this.undoAllowed,
+    @required this.redoAllowed,
   });
 
   @override
@@ -84,17 +89,24 @@ class EditorBottomBar extends StatelessWidget {
               maintainState: true,
               maintainInteractivity: false,
             ),
-            // TODO: Add the undo and redo icons
-            Expanded(
-              child: FlatButton.icon(
-                icon: const Icon(Icons.folder),
-                label: Text(parentFolder.publicName),
-                onPressed: () {
-                  var note = editorState.getNote();
-                  editor.moveNoteToFolderSelected(note);
-                },
-              ),
+            const Spacer(),
+            IconButton(
+              icon: const Icon(Icons.undo),
+              onPressed: undoAllowed ? onUndoSelected : null,
             ),
+            FlatButton.icon(
+              icon: const Icon(Icons.folder),
+              label: Text(parentFolder.publicName),
+              onPressed: () {
+                var note = editorState.getNote();
+                editor.moveNoteToFolderSelected(note);
+              },
+            ),
+            IconButton(
+              icon: const Icon(Icons.redo),
+              onPressed: redoAllowed ? onRedoSelected : null,
+            ),
+            const Spacer(),
             menuIcon,
           ],
           mainAxisAlignment: MainAxisAlignment.center,

lib/editors/checklist_editor.dart

@@ -185,6 +185,8 @@ class ChecklistEditorState extends State<ChecklistEditor>
       ),
       onUndoSelected: _undo,
       onRedoSelected: _redo,
+      undoAllowed: false,
+      redoAllowed: false,
     );
   }
 

lib/editors/journal_editor.dart

@@ -108,6 +108,8 @@ class JournalEditorState extends State<JournalEditor>
       body: editor,
       onUndoSelected: _undo,
       onRedoSelected: _redo,
+      undoAllowed: false,
+      redoAllowed: false,
     );
   }
 

lib/editors/markdown_editor.dart

@@ -142,6 +142,8 @@ class MarkdownEditorState extends State<MarkdownEditor>
       body: editor,
       onUndoSelected: _undo,
       onRedoSelected: _redo,
+      undoAllowed: false,
+      redoAllowed: false,
     );
   }
 

lib/editors/raw_editor.dart

@@ -8,6 +8,7 @@ import 'package:gitjournal/core/md_yaml_doc_codec.dart';
 import 'package:gitjournal/core/note.dart';
 import 'package:gitjournal/editors/common.dart';
 import 'package:gitjournal/editors/disposable_change_notifier.dart';
+import 'package:gitjournal/editors/undo_redo.dart';
 import 'package:gitjournal/widgets/editor_scroll_view.dart';
 
 class RawEditor extends StatefulWidget implements Editor {
@@ -56,12 +57,14 @@ class RawEditorState extends State<RawEditor>
     implements EditorState {
   Note note;
   bool _noteModified;
-  TextEditingController _textController = TextEditingController();
+  TextEditingController _textController;
+  UndoRedoStack _undoRedoStack;
 
   final serializer = MarkdownYAMLCodec();
 
   RawEditorState(this.note) {
     _textController = TextEditingController(text: serializer.encode(note.data));
+    _undoRedoStack = UndoRedoStack();
   }
 
   @override
@@ -106,6 +109,8 @@ class RawEditorState extends State<RawEditor>
       body: editor,
       onUndoSelected: _undo,
       onRedoSelected: _redo,
+      undoAllowed: _undoRedoStack.undoPossible,
+      redoAllowed: _undoRedoStack.redoPossible,
     );
   }
 
@@ -118,6 +123,12 @@ class RawEditorState extends State<RawEditor>
   void _noteTextChanged() {
     notifyListeners();
 
+    var editState = TextEditorState.fromValue(_textController.value);
+    var redraw = _undoRedoStack.textChanged(editState);
+    if (redraw) {
+      setState(() {});
+    }
+
     if (_noteModified) return;
     setState(() {
       _noteModified = true;
@@ -136,9 +147,21 @@ class RawEditorState extends State<RawEditor>
   @override
   bool get noteModified => _noteModified;
 
-  Future<void> _undo() async {}
+  Future<void> _undo() async {
+    var es = _undoRedoStack.undo();
+    _textController.value = es.toValue();
+    setState(() {
+      // To Redraw the undo/redo button state
+    });
+  }
 
-  Future<void> _redo() async {}
+  Future<void> _redo() async {
+    var es = _undoRedoStack.redo();
+    _textController.value = es.toValue();
+    setState(() {
+      // To Redraw the undo/redo button state
+    });
+  }
 }
 
 class _NoteEditor extends StatelessWidget {

lib/editors/scaffold.dart

@@ -24,6 +24,9 @@ class EditorScaffold extends StatefulWidget {
   final Func0<void> onUndoSelected;
   final Func0<void> onRedoSelected;
 
+  final bool undoAllowed;
+  final bool redoAllowed;
+
   EditorScaffold({
     @required this.editor,
     @required this.editorState,
@@ -33,6 +36,8 @@ class EditorScaffold extends StatefulWidget {
     @required this.parentFolder,
     @required this.onUndoSelected,
     @required this.onRedoSelected,
+    @required this.undoAllowed,
+    @required this.redoAllowed,
     this.extraButton,
   });
 
@@ -169,6 +174,8 @@ class _EditorScaffoldState extends State<EditorScaffold> {
                 metaDataEditable: note != null ? note.canHaveMetadata : false,
                 onUndoSelected: widget.onUndoSelected,
                 onRedoSelected: widget.onRedoSelected,
+                undoAllowed: widget.undoAllowed,
+                redoAllowed: widget.redoAllowed,
               ),
             )
           ],

lib/editors/undo_redo.dart

@@ -0,0 +1,57 @@
+import 'dart:math';
+
+import 'package:gitjournal/editors/common.dart';
+
+// FIXME: Possibly conserve memory by only storing the difference between the
+//        texts? Or by saving it to disk?
+
+// FIXME: This should probably also have what field was changed?
+//        How does this work for the title and the checklist editor?
+
+// FIXME: Instead of storing if each note has been modified that should be
+//        be just taken from this class
+//
+class UndoRedoStack {
+  var _versions = <TextEditorState>[];
+  int _index = -1;
+
+  /// Returns if UI should be redrawn
+  bool textChanged(TextEditorState es) {
+    var _redo = redoPossible;
+    var _undo = undoPossible;
+    if (_redo) {
+      var i = max(0, _index);
+      _versions.removeRange(i, _versions.length - 1);
+    }
+    if (_versions.isEmpty) {
+      _versions.add(es);
+      _index = _versions.length - 1;
+      return true;
+    }
+    var last = _versions.last;
+    if (last.text == es.text) {
+      return false;
+    }
+    _versions.add(es);
+    _index = _versions.length - 1;
+
+    return redoPossible != _redo || undoPossible != _undo;
+  }
+
+  TextEditorState undo() {
+    var i = _index;
+    _index--;
+    return _versions[i];
+  }
+
+  TextEditorState redo() {
+    _index++;
+    return _versions[_index];
+  }
+
+  bool get undoPossible => _index >= 0;
+  bool get redoPossible => _index < _versions.length - 1;
+  bool get modified => _versions.isNotEmpty;
+}
+
+// FIXME: Only save it every x seconds?