Divide Originator into Recovery-Backup classes.

patterns/memento/memento_editor/editor/editor.dart

@@ -5,7 +5,8 @@ import '../memento_pattern/originator.dart';
 import '../shapes/shapes.dart';
 import 'manipulator.dart';
 
-class Editor extends ClassicApp with Manipulator, Shapes, Originator {
+class Editor extends ClassicApp
+    with Manipulator, Shapes, BackupOriginator, RecoveryOriginator {
   @override
   void onPaint(Canvas canvas, Size canvasSize) {
     _paintBackground(canvas, canvasSize);

patterns/memento/memento_editor/memento_pattern/originator.dart

@@ -6,37 +6,22 @@ import '../shapes/shapes.dart';
 import '../shapes/shape.dart';
 import 'snapshot.dart';
 
-mixin Originator implements Shapes {
-  Snapshot backup() {
-    final data = _allocateBuffer();
-    _writeShapes(data);
-    _writeSelectedIndex(data);
-    return _toSnapshot(data);
-  }
+const _shapeByteSize = 16;
+const _selectedIndexByteSize = 4;
 
-  void restore(Snapshot snapshot) {
-    final byteData = _fromSnapshotToByteData(snapshot);
-    final newShapes = _readShapes(byteData);
-    final selectedIndex = _readSelectedIndex(byteData);
-    shapes.clear();
-    shapes.addAll(newShapes);
-    selectByIndex(selectedIndex);
+mixin BackupOriginator implements Shapes {
+  Snapshot backup() {
+    final buffer = _allocateBuffer();
+    _writeShapes(buffer);
+    _writeSelectedIndex(buffer);
+    return _toSnapshot(buffer);
   }
 
-  static const _shapeByteSize = 16;
-  static const _selectedIndexByteSize = 4;
-
   ByteData _allocateBuffer() {
     final byteSize = shapes.length * _shapeByteSize + _selectedIndexByteSize;
     return ByteData(byteSize);
   }
 
-  ByteData _fromSnapshotToByteData(Snapshot snapshot) {
-    final unBase = Base64Decoder().convert(snapshot);
-    final byteData = ByteData.sublistView(unBase);
-    return byteData;
-  }
-
   void _writeSelectedIndex(ByteData data) {
     late final int selectedIndex;
 
@@ -59,12 +44,35 @@ mixin Originator implements Shapes {
         ..setFloat32(byteOffset + 4, shape.y)
         ..setInt32(byteOffset + 8, shape.color.value)
         ..setFloat32(byteOffset + 12, shape.size);
-      byteOffset += 16;
+      byteOffset += _shapeByteSize;
     }
 
     return byteOffset;
   }
 
+  Snapshot _toSnapshot(ByteData data) {
+    return Base64Encoder().convert(
+      data.buffer.asUint8List(),
+    );
+  }
+}
+
+mixin RecoveryOriginator implements Shapes {
+  void restore(Snapshot snapshot) {
+    final byteData = _fromSnapshotToByteData(snapshot);
+    final newShapes = _readShapes(byteData);
+    final selectedIndex = _readSelectedIndex(byteData);
+    shapes.clear();
+    shapes.addAll(newShapes);
+    selectByIndex(selectedIndex);
+  }
+
+  ByteData _fromSnapshotToByteData(Snapshot snapshot) {
+    final unBase = Base64Decoder().convert(snapshot);
+    final byteData = ByteData.sublistView(unBase);
+    return byteData;
+  }
+
   int _getNumberOfShapes(ByteData byteData) {
     return (byteData.lengthInBytes - _selectedIndexByteSize) ~/ _shapeByteSize;
   }
@@ -82,7 +90,7 @@ mixin Originator implements Shapes {
         byteData.getFloat32(byteOffset + 12),
       );
       shapes.add(shape);
-      byteOffset += 16;
+      byteOffset += _shapeByteSize;
     }
 
     return shapes;
@@ -91,10 +99,4 @@ mixin Originator implements Shapes {
   int _readSelectedIndex(ByteData byteData) {
     return byteData.getInt32(byteData.lengthInBytes - _selectedIndexByteSize);
   }
-
-  Snapshot _toSnapshot(ByteData data) {
-    return Base64Encoder().convert(
-      data.buffer.asUint8List(),
-    );
-  }
 }