adding packages

deprecated/undo/lib/src/undo_stack.dart

@@ -0,0 +1,92 @@
+import 'dart:collection';
+
+import 'change.dart';
+
+class ChangeStack {
+  /// Changes to keep track of
+  ChangeStack({this.limit});
+
+  /// Limit changes to store in the history
+  int? limit;
+
+  final Queue<List<Change>> _history = ListQueue();
+  final Queue<List<Change>> _redos = ListQueue();
+
+  /// List of changes in the history
+  List<Change> get history => _history.last;
+
+  /// List of changes in the redo stack
+  List<Change> get redos => _redos.first;
+
+  /// Can redo the previous change
+  bool get canRedo => _redos.isNotEmpty;
+
+  /// Can undo the previous change
+  bool get canUndo => _history.isNotEmpty;
+
+  /// Add New Change and Clear Redo Stack
+  void add<T>(Change<T> change) {
+    try {
+      change.execute();
+      _history.addLast([change]);
+      _moveForward();
+    } catch (e) {
+      rethrow;
+    }
+  }
+
+  void _moveForward() {
+    _redos.clear();
+
+    if (limit != null && _history.length > limit! + 1) {
+      _history.removeFirst();
+    }
+  }
+
+  /// Add New Group of Changes and Clear Redo Stack
+  void addGroup<T>(List<Change<T>> changes) {
+    try {
+      _applyChanges(changes);
+      _history.addLast(changes);
+      _moveForward();
+    } catch (e) {
+      rethrow;
+    }
+  }
+
+  void _applyChanges(List<Change> changes) {
+    for (final change in changes) {
+      change.execute();
+    }
+  }
+
+  /// Clear Undo History
+  @deprecated
+  void clear() => clearHistory();
+
+  /// Clear Undo History
+  void clearHistory() {
+    _history.clear();
+    _redos.clear();
+  }
+
+  /// Redo Previous Undo
+  void redo() {
+    if (canRedo) {
+      final changes = _redos.removeFirst();
+      _applyChanges(changes);
+      _history.addLast(changes);
+    }
+  }
+
+  /// Undo Last Change
+  void undo() {
+    if (canUndo) {
+      final changes = _history.removeLast();
+      for (final change in changes) {
+        change.undo();
+      }
+      _redos.addFirst(changes);
+    }
+  }
+}