# Issue #72: Graph Visualization Component

## Objective

Create interactive knowledge graph visualization component in Next.js web UI using the graph API from issue #71.

## Approach

1. Research and select graph visualization library
2. Follow TDD: Write tests before implementation
3. Create graph visualization component with:
   - Force-directed layout
   - Node sizing based on connections
   - PDA-friendly status colors
   - Click handlers for navigation
   - Zoom/pan controls
   - Layout toggle options
4. Performance test with 500+ nodes
5. Integrate with graph API

## Library Selection

Evaluating options:

- **react-force-graph**: WebGL-based, high performance, good for 500+ nodes
- **vis-network**: Canvas-based, feature-rich
- **d3-force**: Low-level, full control but more complex

**Decision: react-force-graph-2d**

- Best performance for 500+ nodes (WebGL rendering)
- Simple API
- Built-in zoom/pan
- Easy to customize node appearance
- Active maintenance

## Progress

- [x] Create scratchpad
- [x] Set up component structure
- [x] Write tests (TDD) - 16 tests, all passing
- [x] Implement basic graph rendering
- [x] Add node sizing logic (based on connection count)
- [x] Add status-based coloring (PDA-friendly colors)
- [x] Implement click handlers (navigation to entry)
- [x] Add layout controls (force, hierarchical, circular)
- [x] Performance testing (supports 500+ nodes)
- [x] Create display page at /knowledge/graph
- [x] Add filters (status, tags, orphans)
- [x] Type checking passes
- [x] Linting passes
- [ ] Code review
- [ ] QA checks
- [ ] Commit and close issue

## Testing Strategy

1. Unit tests for graph component
2. Test node rendering
3. Test interaction handlers
4. Test layout switching
5. Performance test with large datasets

## PDA-Friendly Colors

From CLAUDE.md:

- 🟢 Active: green-500
- 🔵 Scheduled: blue-500
- ⏸️ Paused: yellow-500
- 💤 Dormant: gray-400
- ⚪ Archived: gray-300

## Implementation Summary

### Components Created

1. **KnowledgeGraphViewer.tsx** - Main graph visualization component
   - Force-directed, hierarchical, and circular layout options
   - PDA-friendly status colors (green=published, blue=draft, gray=archived)
   - Node sizing based on connection count
   - Interactive zoom/pan controls
   - Click to navigate to entry
   - Filters: status, tags, orphan visibility
   - Legend panel showing color meanings

2. **KnowledgeGraphViewer.test.tsx** - Comprehensive test suite
   - 16 tests covering all features
   - 100% test pass rate
   - Performance test with 500+ nodes

3. **page.tsx** - Display page at /knowledge/graph

### API Integration

- Added fetchKnowledgeGraph() to knowledge.ts API client
- Fetches from /api/knowledge/graph endpoint (implemented in issue #71)
- Supports filtering by tags, status, and limit

### Libraries Used

- @xyflow/react - Graph rendering and layout
- elkjs - Hierarchical layout algorithm
- Already in package.json, no new dependencies needed

### Features Implemented

- ✅ Force-directed layout (default)
- ✅ Hierarchical layout (ELK algorithm)
- ✅ Circular layout
- ✅ Node sizing based on connections (40px - 120px)
- ✅ PDA-friendly colors by status
- ✅ Orphan node detection and highlighting
- ✅ Click to navigate to entry
- ✅ Zoom and pan controls (ReactFlow built-in)
- ✅ MiniMap for navigation
- ✅ Filters: status, tags, show/hide orphans
- ✅ Statistics display (total nodes, edges, orphans)
- ✅ Legend panel
- ✅ Performance tested with 500+ nodes

### Notes

- Using @xyflow/react instead of react-force-graph (already in dependencies)
- Memoization implemented for filtered nodes/edges
- Layout calculations are async to prevent UI blocking
- All quality gates passed (tests, typecheck, lint)