feat: notify transaction instead of operations

frontend/app_flowy/packages/appflowy_editor/example/lib/main.dart

@@ -109,8 +109,8 @@ class _MyHomePageState extends State<MyHomePage> {
             ..handler = (message) {
               debugPrint(message);
             };
-          _editorState!.operationStream.listen((event) {
-            debugPrint('Operation: ${event.toJson()}');
+          _editorState!.transactionStream.listen((event) {
+            debugPrint('Transaction: ${event.toJson()}');
           });
           return Container(
             color: darkMode ? Colors.black : Colors.white,

frontend/app_flowy/packages/appflowy_editor/lib/src/editor_state.dart

@@ -9,7 +9,7 @@ import 'package:appflowy_editor/src/core/location/selection.dart';
 import 'package:appflowy_editor/src/core/document/document.dart';
 import 'package:appflowy_editor/src/core/transform/operation.dart';
 import 'package:appflowy_editor/src/core/transform/transaction.dart';
-import 'package:appflowy_editor/src/undo_manager.dart';
+import 'package:appflowy_editor/src/history/undo_manager.dart';
 
 class ApplyOptions {
   /// This flag indicates that
@@ -63,8 +63,8 @@ class EditorState {
   EditorStyle editorStyle = EditorStyle.defaultStyle();
 
   /// Operation stream.
-  Stream<Operation> get operationStream => _observer.stream;
-  final StreamController<Operation> _observer = StreamController.broadcast();
+  Stream<Transaction> get transactionStream => _observer.stream;
+  final StreamController<Transaction> _observer = StreamController.broadcast();
 
   final UndoManager undoManager = UndoManager();
   Selection? _cursorSelection;
@@ -140,6 +140,8 @@ class EditorState {
       _applyOperation(op);
     }
 
+    _observer.add(transaction);
+
     WidgetsBinding.instance.addPostFrameCallback((_) {
       updateCursorSelection(transaction.afterSelection);
     });
@@ -187,6 +189,5 @@ class EditorState {
     } else if (op is UpdateTextOperation) {
       document.updateText(op.path, op.delta);
     }
-    _observer.add(op);
   }
 }

frontend/app_flowy/packages/appflowy_editor/lib/src/history/undo_manager.dart

@@ -0,0 +1,152 @@
+import 'dart:collection';
+
+import 'package:appflowy_editor/src/core/location/selection.dart';
+import 'package:appflowy_editor/src/infra/log.dart';
+import 'package:appflowy_editor/src/core/transform/operation.dart';
+import 'package:appflowy_editor/src/core/transform/transaction.dart';
+import 'package:appflowy_editor/src/editor_state.dart';
+
+/// A [HistoryItem] contains list of operations committed by users.
+/// If a [HistoryItem] is not sealed, operations can be added sequentially.
+/// Otherwise, the operations should be added to a new [HistoryItem].
+class HistoryItem extends LinkedListEntry<HistoryItem> {
+  final List<Operation> operations = [];
+  Selection? beforeSelection;
+  Selection? afterSelection;
+  bool _sealed = false;
+
+  HistoryItem();
+
+  /// Seal the history item.
+  /// When an item is sealed, no more operations can be added
+  /// to the item.
+  ///
+  /// The caller should create a new [HistoryItem].
+  seal() {
+    _sealed = true;
+  }
+
+  bool get sealed => _sealed;
+
+  add(Operation op) {
+    operations.add(op);
+  }
+
+  addAll(Iterable<Operation> iterable) {
+    operations.addAll(iterable);
+  }
+
+  /// Create a new [Transaction] by inverting the operations.
+  Transaction toTransaction(EditorState state) {
+    final builder = Transaction(document: state.document);
+    for (var i = operations.length - 1; i >= 0; i--) {
+      final operation = operations[i];
+      final inverted = operation.invert();
+      builder.add(inverted, transform: false);
+    }
+    builder.afterSelection = beforeSelection;
+    builder.beforeSelection = afterSelection;
+    return builder;
+  }
+}
+
+class FixedSizeStack {
+  final _list = LinkedList<HistoryItem>();
+  final int maxSize;
+
+  FixedSizeStack(this.maxSize);
+
+  push(HistoryItem stackItem) {
+    if (_list.length >= maxSize) {
+      _list.remove(_list.first);
+    }
+    _list.add(stackItem);
+  }
+
+  HistoryItem? pop() {
+    if (_list.isEmpty) {
+      return null;
+    }
+    final last = _list.last;
+
+    _list.remove(last);
+
+    return last;
+  }
+
+  clear() {
+    _list.clear();
+  }
+
+  HistoryItem get last => _list.last;
+
+  bool get isEmpty => _list.isEmpty;
+
+  bool get isNonEmpty => _list.isNotEmpty;
+}
+
+class UndoManager {
+  final FixedSizeStack undoStack;
+  final FixedSizeStack redoStack;
+  EditorState? state;
+
+  UndoManager([int stackSize = 20])
+      : undoStack = FixedSizeStack(stackSize),
+        redoStack = FixedSizeStack(stackSize);
+
+  HistoryItem getUndoHistoryItem() {
+    if (undoStack.isEmpty) {
+      final item = HistoryItem();
+      undoStack.push(item);
+      return item;
+    }
+    final last = undoStack.last;
+    if (last.sealed) {
+      redoStack.clear();
+      final item = HistoryItem();
+      undoStack.push(item);
+      return item;
+    }
+    return last;
+  }
+
+  undo() {
+    Log.editor.debug('undo');
+    final s = state;
+    if (s == null) {
+      return;
+    }
+    final historyItem = undoStack.pop();
+    if (historyItem == null) {
+      return;
+    }
+    final transaction = historyItem.toTransaction(s);
+    s.apply(
+      transaction,
+      const ApplyOptions(
+        recordUndo: false,
+        recordRedo: true,
+      ),
+    );
+  }
+
+  redo() {
+    Log.editor.debug('redo');
+    final s = state;
+    if (s == null) {
+      return;
+    }
+    final historyItem = redoStack.pop();
+    if (historyItem == null) {
+      return;
+    }
+    final transaction = historyItem.toTransaction(s);
+    s.apply(
+      transaction,
+      const ApplyOptions(
+        recordUndo: true,
+        recordRedo: false,
+      ),
+    );
+  }
+}

frontend/app_flowy/packages/appflowy_editor/test/legacy/undo_manager_test.dart

@@ -1,6 +1,6 @@
 import 'dart:collection';
 import 'package:appflowy_editor/appflowy_editor.dart';
-import 'package:appflowy_editor/src/undo_manager.dart';
+import 'package:appflowy_editor/src/history/undo_manager.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 void main() async {