# Scanner PWA - Offline-First Ticket Scanning

## Overview

The BCT Scanner is an offline-first Progressive Web App (PWA) designed for gate staff to scan tickets even without an internet connection. It features automatic background sync, conflict resolution, and a mobile-optimized interface.

## Features

### Core Functionality
- **QR Code Scanning**: Uses native BarcodeDetector API with ZXing fallback
- **Offline Operation**: Full functionality without internet connection
- **Background Sync**: Automatic synchronization when connection is restored
- **Conflict Resolution**: Handles duplicate scans and offline/online discrepancies
- **Multi-Device Support**: Unique device identification for analytics
- **Zone/Gate Tracking**: Configurable location identification

### User Experience
- **Optimistic UI**: Instant feedback even when offline
- **Haptic Feedback**: Vibration patterns for scan results
- **Audio Feedback**: Sound confirmation for successful scans
- **Torch Control**: Automatic and manual flashlight control
- **Responsive Design**: Optimized for mobile devices
- **PWA Features**: Installable, works offline, background sync

## Installation & Setup

### 1. PWA Installation

**Mobile (iOS/Android):**
1. Open `/scan?eventId=your-event-id` in browser
2. Look for "Add to Home Screen" prompt
3. Follow device-specific installation steps

**Desktop:**
1. Navigate to scanner page
2. Look for install prompt in address bar
3. Click "Install" to add to desktop

### 2. Camera Permissions

The scanner requires camera access:
- **First Visit**: Browser will prompt for camera permission
- **Grant Access**: Select "Allow" to enable scanning
- **Denied Access**: Use settings to re-enable camera permission

### 3. Device Configuration

Set your gate/zone identifier in scanner settings:
1. Click settings icon (gear) in header
2. Enter zone name (e.g., "Gate A", "Main Entrance")
3. Zone is saved locally and included in scan logs

## Usage Guide

### Basic Scanning

1. **Access Scanner**: Navigate to `/scan?eventId={eventId}`
2. **Position QR Code**: Center QR code within scanning frame
3. **Wait for Scan**: Scanner automatically detects and processes codes
4. **View Result**: Status banner shows scan result with color coding

### Scan Results

**Success (Green)**
- Valid ticket, entry allowed
- Shows ticket information (event, type, customer)

**Already Scanned (Yellow)**
- Ticket previously used
- Shows original scan timestamp

**Invalid (Red)**
- Invalid or expired ticket
- Shows error reason

**Offline Accepted (Blue)**
- Accepted in offline mode (if optimistic mode enabled)
- Will be verified when connection restored

### Settings Configuration

**Optimistic Accept (Default: ON)**
- When enabled: Show success for scans when offline
- When disabled: Queue scans for later verification

**Zone/Gate Setting**
- Identifies scanning location
- Included in all scan logs for analytics
- Persisted locally across sessions

**Audio/Haptic Feedback**
- Success: Short beep + brief vibration
- Already Scanned: Double vibration
- Invalid: Long vibration

## Offline Behavior

### How It Works

1. **Scan Detection**: QR codes are processed immediately
2. **Local Storage**: Scans stored in IndexedDB queue
3. **Optimistic UI**: Instant feedback based on settings
4. **Background Sync**: Automatic verification when online
5. **Conflict Detection**: Handles offline/online discrepancies

### Queue Management

**Pending Scans**
- Stored locally until internet connection restored
- Automatically synced with exponential backoff
- Retry logic handles temporary failures

**Sync Status**
- Total scans: All scans from this device
- Pending sync: Queued scans awaiting verification
- Last sync: Timestamp of most recent successful sync

### Conflict Resolution

**Conflict Scenarios**
- Offline scan shows "success" but server says "already scanned"
- Multiple devices scan same ticket while offline

**Resolution Process**
1. Conflicts automatically logged when detected
2. Admin can review conflict log in settings
3. Manual resolution may be required for edge cases

## Technical Architecture

### Frontend Components

```
src/features/scanner/
├── ScannerPage.tsx          # Main scanner interface
├── useScanner.ts            # Camera/scanning hook
├── useScanQueue.ts          # Offline queue management
└── types.ts                 # TypeScript definitions
```

### Offline Storage

**IndexedDB Database: `sentinel_scans`**
- `scans`: Individual scan records with sync status
- `conflicts`: Offline/online result discrepancies
- `settings`: User preferences and device configuration

### Background Sync

**Service Worker** (`/public/sw.js`)
- Handles background synchronization
- Caches essential assets for offline use
- Manages retry logic with exponential backoff

### API Endpoints

**Verification**: `/api/tickets/verify`
- Validates QR codes against ticket database
- Returns ticket information and scan history

**Logging**: `/api/scans/log`
- Records scan events for analytics
- Includes device, zone, and timing information

## Security & Access Control

### Authentication
- **Required**: User must be authenticated to access scanner
- **Permissions**: Requires `scan:tickets` permission
- **Roles**: Available to staff, organizers, and admins

### Data Protection
- **Local Storage**: Encrypted scan queue in IndexedDB
- **Device ID**: Unique identifier for tracking (not personally identifiable)
- **No Secrets**: All verification happens server-side

## Testing

### Running Tests

```bash
# All scanner tests
npm run test tests/scan-offline.spec.ts

# With UI (helpful for debugging)
npm run test:ui tests/scan-offline.spec.ts

# Headed mode (see actual browser)
npm run test:headed tests/scan-offline.spec.ts
```

### Test Coverage

**Online Scenarios**
1. Valid ticket scan → success + server verification
2. Invalid ticket scan → error from server
3. Duplicate scan → already_scanned response

**Offline Scenarios**
1. Offline scan with optimistic ON → immediate success
2. Offline scan with optimistic OFF → queued status
3. Connection restored → background sync processes queue

**Conflict Scenarios**
1. Offline success + server already_scanned → conflict logged
2. Multiple device conflicts → resolution workflow

**Access Control**
1. Unauthenticated user → redirect to login
2. User without scan permission → unauthorized error
3. Staff/admin user → scanner access granted

## Troubleshooting

### Common Issues

**Camera Not Working**
- Check browser permissions in settings
- Try different browser (Chrome/Firefox recommended)
- Ensure HTTPS connection (required for camera access)

**Scans Not Syncing**
- Check internet connection
- Open settings to view pending sync count
- Use "Force Sync" button if available

**App Not Installing**
- Ensure HTTPS connection
- Clear browser cache and retry
- Check if PWA is already installed

**Performance Issues**
- Close other camera-using apps
- Restart browser
- Clear scanner app data and reinstall

### Browser Support

**Recommended Browsers**
- Chrome 88+ (best performance)
- Safari 14+ (iOS support)
- Firefox 85+ (good fallback)
- Edge 88+ (Windows support)

**Required Features**
- Camera API (getUserMedia)
- IndexedDB (offline storage)
- Service Workers (background sync)
- Web App Manifest (PWA installation)

### Debugging Tools

**Browser DevTools**
- Application tab → Service Workers (check registration)
- Application tab → IndexedDB (view scan queue)
- Console tab → Look for scanner logs
- Network tab → Monitor API calls

**Scanner Settings**
- View pending sync count
- Check last sync timestamp
- Review conflict log
- Force manual sync

## Analytics & Monitoring

### Scan Metrics

**Per Device**
- Total scans processed
- Success/failure rates
- Average scan time
- Offline vs online scans

**Per Event**
- Device coverage (zones/gates)
- Peak scanning times
- Conflict rates
- Sync latency

### Data Export

Scan data can be exported for analysis:
- Individual scan records with timestamps
- Device and zone information
- Sync status and conflicts
- Customer and ticket details

## API Reference

### Scanner API Service

```typescript
// Verify a QR code
const result = await api.scanner.verifyTicket(qrCode);

// Log scan event (fire-and-forget)
await api.scanner.logScan({
  eventId: 'evt-123',
  qr: 'TICKET_456',
  deviceId: 'device_789',
  zone: 'Gate A',
  result: 'valid',
  latency: 250
});

// Get scan history
const history = await api.scanner.getScanHistory(eventId, page, pageSize);
```

### Response Formats

**Verify Response**
```json
{
  "valid": true,
  "reason": "already_scanned", // if invalid
  "scannedAt": "2024-01-01T12:00:00Z", // if duplicate
  "ticketInfo": {
    "eventTitle": "Sample Event",
    "ticketTypeName": "General Admission",
    "customerEmail": "customer@example.com",
    "seatNumber": "A-15" // if assigned seating
  }
}
```

## Best Practices

### For Gate Staff

1. **Keep Device Charged**: Scanner is power-intensive
2. **Good Lighting**: Use torch in dark environments
3. **Steady Hands**: Hold device stable for better scanning
4. **Check Sync**: Periodically verify pending sync count
5. **Report Issues**: Note any conflicts or unusual behavior

### For Event Managers

1. **Test Before Event**: Verify scanner works with sample tickets
2. **Multiple Devices**: Deploy scanners at all entry points
3. **Backup Plan**: Have manual ticket list as fallback
4. **Monitor Conflicts**: Review conflict logs after event
5. **Network Planning**: Ensure WiFi coverage at gates

### For Developers

1. **Error Handling**: Graceful degradation when camera fails
2. **Performance**: Optimize for mobile device constraints
3. **Security**: Never store sensitive data locally
4. **Testing**: Include both online and offline scenarios
5. **Monitoring**: Track sync success rates and latency

## Future Enhancements

### Planned Features
- **Bulk Scan Mode**: Rapid scanning for high-volume events
- **Advanced Analytics**: Real-time dashboard for scan monitoring
- **Multi-Event Support**: Switch between events without app restart
- **Biometric Integration**: Facial recognition for VIP verification
- **Inventory Alerts**: Real-time capacity warnings

### Technical Improvements
- **WebAssembly Scanner**: Faster QR code detection
- **Machine Learning**: Improved camera auto-focus
- **Push Notifications**: Sync status and conflict alerts
- **Cloud Sync**: Cross-device scan sharing
- **Advanced PWA**: Enhanced installation and app store distribution