Implement Undo/Redo Stack with Command Pattern #34

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2026-03-27T23:18:03Z

thib8956 commented

2026-03-27 23:18:03 +00:00

Overview

Implement undo/redo functionality with a command history stack.

Current State

Controller handles shape operations (add, delete, move, color change)
No command history exists
Selection system tracks selected shapes

Implementation Plan

1. Command pattern

Create Command interface with execute() and undo() methods
Create concrete commands:
- AddShapeCommand - stores shape reference, removes on undo
- DeleteShapesCommand - stores shapes list, re-adds on undo
- MoveShapeCommand - stores shape, original pos, new pos
- ChangeColorCommand - stores shape, old/new colors
- ResizeCommand - stores shape, old/new bounds
- GroupCommand - composite for batch operations

2. CommandManager class

Maintains two stacks: undoStack, redoStack
execute(Command): push to undoStack, clear redoStack
undo(): pop from undoStack, call undo(), push to redoStack
redo(): pop from redoStack, call execute(), push to undoStack
Limit stack size (e.g., 50 commands)

3. Controller integration

Replace direct shape operations with commands
Example: instead of collection.add(shape), do commandManager.execute(new AddShapeCommand(shape, collection))

4. Keyboard shortcuts

Ctrl+Z: undo
Ctrl+Y: redo (or Ctrl+Shift+Z)
Update menu with these shortcuts

5. Menu additions

Add Edit menu items: Undo, Redo
Enable/disable based on stack state

Files to create/modify

Create: commands/Command.java, commands/CommandManager.java
Create: commands/AddShapeCommand.java, commands/DeleteShapesCommand.java, commands/MoveShapeCommand.java, etc.
Modify: ui/Controller.java, App.java (menu)

Edge cases

Copy/paste after undo: clear redo stack
Multi-select delete: single compound command
Application close: no persistence needed (in-memory only)

## Overview Implement undo/redo functionality with a command history stack. ## Current State - Controller handles shape operations (add, delete, move, color change) - No command history exists - Selection system tracks selected shapes ## Implementation Plan ### 1. Command pattern - Create Command interface with execute() and undo() methods - Create concrete commands: - AddShapeCommand - stores shape reference, removes on undo - DeleteShapesCommand - stores shapes list, re-adds on undo - MoveShapeCommand - stores shape, original pos, new pos - ChangeColorCommand - stores shape, old/new colors - ResizeCommand - stores shape, old/new bounds - GroupCommand - composite for batch operations ### 2. CommandManager class - Maintains two stacks: undoStack, redoStack - execute(Command): push to undoStack, clear redoStack - undo(): pop from undoStack, call undo(), push to redoStack - redo(): pop from redoStack, call execute(), push to undoStack - Limit stack size (e.g., 50 commands) ### 3. Controller integration - Replace direct shape operations with commands - Example: instead of collection.add(shape), do commandManager.execute(new AddShapeCommand(shape, collection)) ### 4. Keyboard shortcuts - Ctrl+Z: undo - Ctrl+Y: redo (or Ctrl+Shift+Z) - Update menu with these shortcuts ### 5. Menu additions - Add Edit menu items: Undo, Redo - Enable/disable based on stack state ## Files to create/modify - Create: commands/Command.java, commands/CommandManager.java - Create: commands/AddShapeCommand.java, commands/DeleteShapesCommand.java, commands/MoveShapeCommand.java, etc. - Modify: ui/Controller.java, App.java (menu) ## Edge cases - Copy/paste after undo: clear redo stack - Multi-select delete: single compound command - Application close: no persistence needed (in-memory only)

thib8956 referenced this issue from a commit

2026-03-27 23:57:48 +00:00

Implement #34: Undo/Redo Stack with Command Pattern

thib8956 referenced this issue

2026-03-27 23:58:07 +00:00

Implement #34: Undo/Redo with Command Pattern #41

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Reference: thib8956/new-shapes#34