# Watcher Health Monitoring Implementation Summary

## What Was Implemented

A comprehensive health monitoring and automatic recovery system for the file watcher service to ensure it continues running and automatically recovers if it crashes.

## Files Created

1. **Backend Service** - `/apps/service/src/watcher-health.service.ts`
   - Monitors watcher health every 30 seconds
   - Detects unexpected watcher stops
   - Logs all errors to database
   - Implements automatic recovery with configurable limits
   - Provides health status and error log APIs

2. **Frontend Component** - `/apps/web/src/app/components/WatcherHealthStatus.tsx`
   - Displays real-time watcher health status (green/red indicator)
   - Shows recent error logs with timestamps
   - Allows viewing and clearing error history
   - Toggle button to enable/disable auto-recovery
   - WebSocket integration for real-time updates

3. **Documentation** - `/docs/WATCHER_HEALTH_MONITORING.md`
   - Complete feature documentation
   - Architecture overview
   - API endpoint reference
   - Configuration guide
   - Troubleshooting tips

## Files Modified

1. **App Module** - `/apps/service/src/app.module.ts`
   - Added `WatcherHealthService` to providers

2. **App Service** - `/apps/service/src/app.service.ts`
   - Added health check method wrappers:
     - `watcherHealthStatus()`
     - `watcherRecentErrors(limit?)`
     - `clearWatcherErrors()`
     - `setWatcherAutoRecovery(enabled)`
     - `isWatcherAutoRecoveryEnabled()`

3. **App Controller** - `/apps/service/src/app.controller.ts`
   - Added 6 new HTTP endpoints:
     - `GET /watcher/health` - Get health status
     - `GET /watcher/errors` - List recent errors
     - `DELETE /watcher/errors` - Clear error logs
     - `POST /watcher/auto-recovery` - Set auto-recovery status
     - `GET /watcher/auto-recovery` - Get auto-recovery status

4. **Watcher Service** - `/apps/service/src/watcher.service.ts`
   - Added `ready` event listener to log when watcher is ready

5. **Stats Section** - `/apps/web/src/app/components/StatsSection.tsx`
   - Imported and integrated `WatcherHealthStatus` component
   - Added full-width health monitoring section to dashboard

## Key Features

### Health Monitoring

- ✅ Continuous monitoring every 30 seconds
- ✅ Detects when watcher unexpectedly stops
- ✅ Real-time status updates via WebSocket

### Error Logging

- ✅ All errors logged to `watcher_errors` database table
- ✅ Automatic cleanup (keeps last 100 errors)
- ✅ Accessible via API and web UI

### Automatic Recovery

- ✅ Configurable enable/disable
- ✅ Intelligent restart with last known configuration
- ✅ Recovery limiting (5 attempts per hour)
- ✅ Comprehensive logging of recovery attempts
- ✅ Automatic attempt counter reset after success

### User Interface

- ✅ Health status dashboard with green/red indicator
- ✅ Error log viewer with timestamps
- ✅ Clear error logs button
- ✅ Auto-recovery toggle
- ✅ Real-time updates via WebSocket
- ✅ Toast notifications for user feedback

## How It Works

```
User starts watcher
    ↓
WatcherHealthService begins monitoring
    ↓
Every 30 seconds: Health check runs
    ↓
Is watcher still running?
    ├─ YES: Continue monitoring (no action)
    └─ NO:
        ├─ Log error to database
        ├─ Emit WebSocket alert to UI
        └─ If auto-recovery enabled:
            ├─ Attempt restart with last config
            ├─ Log recovery attempt
            ├─ If successful: Reset attempt counter
            └─ If failed: Increment counter (max 5/hour)
```

## Configuration

Auto-recovery is **enabled by default**. Users can:

1. **Disable via UI** - Click "Disable" in the Auto-Recovery section
2. **Disable via API** - `POST /watcher/auto-recovery { "enabled": false }`
3. **Disable via database** - Set `watcher_auto_recovery` setting to false

## Testing the Feature

1. Start the watcher through the web UI
2. Kill the watcher process: `pkill -f "watcher"`
3. Observe automatic recovery (within 30 seconds):
   - Watcher should restart automatically
   - Dashboard should show recovery in progress
   - Error logs should record the failure
4. Check error logs: Click "View Errors" in the health panel
5. Clear logs: Click "Clear Log" button

## API Usage Examples

```bash
# Get health status
curl http://localhost:3001/watcher/health

# Get recent errors
curl http://localhost:3001/watcher/errors?limit=20

# Clear error logs
curl -X DELETE http://localhost:3001/watcher/errors

# Enable auto-recovery
curl -X POST http://localhost:3001/watcher/auto-recovery \
  -H "Content-Type: application/json" \
  -d '{"enabled": true}'

# Check auto-recovery status
curl http://localhost:3001/watcher/auto-recovery
```

## Build Status

✅ **Build successful** - All TypeScript compiles without errors
✅ **Tests** - Existing tests continue to pass
✅ **No breaking changes** - Fully backward compatible

## Database Changes

New table created automatically on first run:

```sql
CREATE TABLE IF NOT EXISTS watcher_errors (
  id INTEGER PRIMARY KEY AUTOINCREMENT,
  timestamp TEXT NOT NULL,
  message TEXT NOT NULL,
  recovery_attempt INTEGER DEFAULT 0,
  created_at TEXT NOT NULL
);
```

No existing tables or data are affected.

## Next Steps

Users can now:

1. Monitor watcher health in real-time
2. View detailed error logs with timestamps
3. Enable/disable automatic recovery as needed
4. Troubleshoot watcher issues more easily
5. Ensure watcher is always running when configured

## Support

For detailed information, see `/docs/WATCHER_HEALTH_MONITORING.md`