constellation-analyzer/docs/UNDO_REDO_IMPLEMENTATION.md

Undo/Redo System Implementation

Overview

The Constellation Analyzer now features a comprehensive per-document undo/redo system that allows users to safely experiment with their graphs without fear of permanent mistakes.

Key Features:

• ✅ Per-Document History: Each document maintains its own independent undo/redo stack (max 50 actions)
• ✅ Keyboard Shortcuts: Ctrl+Z (undo), Ctrl+Y or Ctrl+Shift+Z (redo)
• ✅ Visual UI: Undo/Redo buttons in toolbar with disabled states and tooltips
• ✅ Action Descriptions: Hover tooltips show what action will be undone/redone
• ✅ Automatic Tracking: All graph operations are automatically tracked
• ✅ Debounced Moves: Node dragging is debounced to avoid cluttering history
• ✅ Document Switching: History is preserved when switching between documents

Architecture

1. History Store (src/stores/historyStore.ts)

The central store manages history for all documents:

{
  histories: Map<documentId, DocumentHistory>
  maxHistorySize: 50
}

Each DocumentHistory contains:

• undoStack: Array of past actions (most recent at end)
• redoStack: Array of undone actions that can be redone
• currentState: The current document state snapshot

Key Methods:

• pushAction(documentId, action): Records a new action
• undo(documentId): Reverts to previous state
• redo(documentId): Restores undone state
• canUndo/canRedo(documentId): Check if actions available
• initializeHistory(documentId, initialState): Setup history for new document
• removeHistory(documentId): Clean up when document deleted

2. Document History Hook (src/hooks/useDocumentHistory.ts)

Provides high-level undo/redo functionality for the active document:

const { undo, redo, canUndo, canRedo, undoDescription, redoDescription, pushToHistory } = useDocumentHistory();

Responsibilities:

• Initializes history when document is first loaded
• Provides pushToHistory(description) to record actions
• Handles undo/redo by restoring document state
• Updates both graphStore and workspaceStore on undo/redo
• Marks documents as dirty after undo/redo

3. Graph Operations with History (src/hooks/useGraphWithHistory.ts)

OPTIONAL WRAPPER: This hook wraps all graph operations with automatic history tracking.

const { addNode, updateNode, deleteNode, addEdge, ... } = useGraphWithHistory();

Features:

• Debounces node position changes (500ms) to avoid cluttering history during dragging
• Immediate history push for add/delete operations
• Smart action descriptions (e.g., "Add Person Actor", "Delete Collaborates Relation")
• Prevents recursive history pushes during undo/redo restore

Note: This is an alternative to manually calling pushToHistory() after each operation.

4. Keyboard Shortcuts (src/hooks/useKeyboardShortcuts.ts)

Extended to support undo/redo:

useKeyboardShortcuts({
  onUndo: undo,
  onRedo: redo,
  // ... other shortcuts
});

Handles:

• Ctrl+Z / Cmd+Z: Undo
• Ctrl+Y / Cmd+Y: Redo
• Ctrl+Shift+Z / Cmd+Shift+Z: Alternative redo

5. Toolbar UI (src/components/Toolbar/Toolbar.tsx)

Displays undo/redo buttons with visual feedback:

• Undo Button: Shows "Undo: [action description] (Ctrl+Z)" on hover
• Redo Button: Shows "Redo: [action description] (Ctrl+Y)" on hover
• Buttons are disabled (grayed out) when no actions available
• Uses Material-UI icons (UndoIcon, RedoIcon)

6. App Integration (src/App.tsx)

Connects keyboard shortcuts to undo/redo functionality:

const { undo, redo } = useDocumentHistory();

useKeyboardShortcuts({
  onUndo: undo,
  onRedo: redo,
});

Usage

Option A: Manual History Tracking

Components can manually record actions:

import { useDocumentHistory } from '../hooks/useDocumentHistory';

function MyComponent() {
  const { pushToHistory } = useDocumentHistory();
  const graphStore = useGraphStore();

  const handleAddNode = () => {
    graphStore.addNode(newNode);
    pushToHistory('Add Person Actor');
  };
}

Option B: Automatic with useGraphWithHistory

Replace useGraphStore() with useGraphWithHistory():

import { useGraphWithHistory } from '../hooks/useGraphWithHistory';

function MyComponent() {
  const { addNode } = useGraphWithHistory();

  const handleAddNode = () => {
    addNode(newNode); // Automatically tracked!
  };
}

Current Implementation

The current codebase uses Option A (manual tracking). Components like GraphEditor and Toolbar use useGraphStore() directly.

To enable automatic tracking, update components to use useGraphWithHistory() instead of useGraphStore().

How It Works: Undo/Redo Flow

Recording an Action

1. User performs action (e.g., adds a node)
2. pushToHistory('Add Person Actor') is called
3. Current document state is snapshotted
4. Snapshot is pushed to undoStack
5. redoStack is cleared (since new action invalidates redo)

Performing Undo

1. User presses Ctrl+Z or clicks Undo button
2. Last action is popped from undoStack
3. Current state is pushed to redoStack
4. Previous state from action is restored
5. GraphStore and WorkspaceStore are updated
6. Document marked as dirty

Performing Redo

1. User presses Ctrl+Y or clicks Redo button
2. Last undone action is popped from redoStack
3. Current state is pushed to undoStack
4. Future state from undone action is restored
5. GraphStore and WorkspaceStore are updated
6. Document marked as dirty

Per-Document Independence

Critical Feature: Each document has completely separate history.

Example workflow:

1. Document A: Add 3 nodes
2. Switch to Document B: Add 2 edges
3. Switch back to Document A: Can still undo those 3 node additions
4. Switch back to Document B: Can still undo those 2 edge additions

History stacks are preserved across document switches and remain independent.

Performance Considerations

Memory Management

• Max 50 actions per document (configurable via MAX_HISTORY_SIZE)
• Old actions are automatically removed when limit exceeded
• History is removed when document is deleted
• Document states use deep cloning to prevent mutation issues

Debouncing

• Node position updates are debounced (500ms) to group multiple moves
• Add/delete operations are immediate (0ms delay)
• Prevents hundreds of history entries when dragging nodes

Testing Checklist

• Create history store
• Create useDocumentHistory hook
• Add keyboard shortcuts (Ctrl+Z, Ctrl+Y, Ctrl+Shift+Z)
• Add undo/redo buttons to toolbar
• Show action descriptions in tooltips
• Disable buttons when no actions available
• Test: Add node → Undo → Node disappears
• Test: Delete node → Undo → Node reappears with connections
• Test: Move node → Undo → Node returns to original position
• Test: Add edge → Undo → Edge disappears
• Test: Update node properties → Undo → Properties restored
• Test: Multiple operations → Undo multiple times → Redo multiple times
• Test: Document A changes → Switch to Document B → Changes independent
• Test: 51 actions → Oldest action removed from history
• Test: Undo then new action → Redo stack cleared
• Test: Keyboard shortcuts work (Ctrl+Z, Ctrl+Y)

Future Enhancements

1. History Panel: Show list of all actions with ability to jump to specific point
2. Persistent History: Save history to localStorage (survives page refresh)
3. Collaborative Undo: Undo operations in multi-user scenarios
4. Selective Undo: Undo specific actions, not just chronological
5. History Branching: Tree-based history (like Git) instead of linear
6. Action Grouping: Combine related actions (e.g., "Add 5 nodes" instead of 5 separate entries)
7. Undo Metadata: Store viewport position, selection state with each action
8. History Analytics: Track most common actions, undo patterns

Implementation Notes

Why Deep Cloning?

Document states are deep cloned using JSON.parse(JSON.stringify()) to prevent mutation:

const snapshot = JSON.parse(JSON.stringify(currentDoc));

This ensures that modifying the current state doesn't affect historical snapshots.

Why Separate undoStack and redoStack?

Standard undo/redo pattern:

• undoStack: Stores past states
• redoStack: Stores undone states that can be restored

When a new action occurs, redoStack is cleared because the "future" is no longer valid.

Why Per-Document History?

Users expect each document to maintain independent history, similar to:

• Text editors (each file has own undo stack)
• Image editors (each image has own history)
• IDEs (each file has own history)

This matches user mental model and prevents confusion.

File Structure

src/
├── stores/
│   └── historyStore.ts              # Central history management
├── hooks/
│   ├── useDocumentHistory.ts        # Per-document undo/redo
│   ├── useGraphWithHistory.ts       # Automatic history tracking wrapper
│   └── useKeyboardShortcuts.ts      # Keyboard shortcuts (extended)
├── components/
│   └── Toolbar/
│       └── Toolbar.tsx              # UI buttons for undo/redo
└── App.tsx                          # Connects keyboard shortcuts

Conclusion

The undo/redo system provides a safety net for users, encouraging experimentation without fear of permanent mistakes. Each document maintains independent history, operations are automatically tracked, and the UI provides clear feedback about available undo/redo actions.

Status: ✅ Implementation Complete (Ready for Testing)

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Implemented: 2025-10-09 Based on: UX_ANALYSIS.md recommendations (Priority: CRITICAL)