# Flutter Barcode Scanner App Guidelines

## App Overview
Simple barcode scanner app with two screens:
1. **Home Screen**: Barcode scanner + scan result display + history list
2. **Detail Screen**: 4 text fields + Save (API call) & Print buttons

## Project Structure
```
lib/
  core/
    constants/
    theme/
    widgets/
    network/
      api_client.dart
  features/
    scanner/
      data/
        datasources/
          scanner_remote_datasource.dart
        models/
          scan_item.dart
          save_request_model.dart
        repositories/
          scanner_repository.dart
      domain/
        entities/
          scan_entity.dart
        repositories/
          scanner_repository.dart
        usecases/
          save_scan_usecase.dart
      presentation/
        providers/
          scanner_provider.dart
        pages/
          home_page.dart
          detail_page.dart
        widgets/
          barcode_scanner_widget.dart
          scan_result_display.dart
          scan_history_list.dart
  main.dart
```

## App Flow
1. **Scan Barcode**: Camera scans → Show result below scanner
2. **Tap Result**: Navigate to detail screen
3. **Fill Form**: Enter data in 4 text fields
4. **Save**: Call API to save data + store locally
5. **Print**: Print form data

## Data Models
```dart
class ScanItem {
  final String barcode;
  final DateTime timestamp;
  final String field1;
  final String field2;
  final String field3;
  final String field4;
  
  ScanItem({
    required this.barcode,
    required this.timestamp,
    this.field1 = '',
    this.field2 = '',
    this.field3 = '',
    this.field4 = '',
  });
}

class SaveRequest {
  final String barcode;
  final String field1;
  final String field2;
  final String field3;
  final String field4;
  
  SaveRequest({
    required this.barcode,
    required this.field1,
    required this.field2,
    required this.field3,
    required this.field4,
  });
  
  Map<String, dynamic> toJson() => {
    'barcode': barcode,
    'field1': field1,
    'field2': field2,
    'field3': field3,
    'field4': field4,
  };
}
```

## Home Screen Layout
```
┌─────────────────────────┐
│                         │
│    Barcode Scanner      │
│     (Camera View)       │
│                         │
├─────────────────────────┤
│  Last Scanned: 123456   │
│    [Tap to edit]        │
├─────────────────────────┤
│    Scan History         │
│  • 123456 - 10:30 AM    │
│  • 789012 - 10:25 AM    │
│  • 345678 - 10:20 AM    │
│                         │
└─────────────────────────┘
```

## Detail Screen Layout
```
┌─────────────────────────┐
│   Barcode: 123456789    │
├─────────────────────────┤
│                         │
│ Field 1: [____________] │
│                         │
│ Field 2: [____________] │
│                         │
│ Field 3: [____________] │
│                         │
│ Field 4: [____________] │
│                         │
├─────────────────────────┤
│   [Save]     [Print]    │
└─────────────────────────┘
```

## Key Features

### Barcode Scanner
- Use **mobile_scanner** package
- Support Code128 and common formats
- Show scanned value immediately below scanner
- Add to history list automatically

### API Integration
- Call API when Save button is pressed
- Send form data to server
- Handle success/error responses
- Show loading state during API call

### Local Storage
- Use **Hive** for simple local storage
- Store scan history with timestamps
- Save form data after successful API call

### Navigation
- Tap on scan result → Navigate to detail screen
- Pass barcode value to detail screen
- Simple back navigation

## State Management (Riverpod)

### Scanner State
```dart
class ScannerState {
  final String? currentBarcode;
  final List<ScanItem> history;
  
  ScannerState({
    this.currentBarcode,
    this.history = const [],
  });
}
```

### Form State
```dart  
class FormState {
  final String barcode;
  final String field1;
  final String field2; 
  final String field3;
  final String field4;
  final bool isLoading;
  final String? error;
  
  FormState({
    required this.barcode,
    this.field1 = '',
    this.field2 = '',
    this.field3 = '',
    this.field4 = '',
    this.isLoading = false,
    this.error,
  });
}
```

## Use Cases

### Save Scan Use Case
```dart
class SaveScanUseCase {
  final ScannerRepository repository;
  
  SaveScanUseCase(this.repository);
  
  Future<Either<Failure, void>> call(SaveRequest request) async {
    return await repository.saveScan(request);
  }
}
```

## Repository Pattern
```dart
abstract class ScannerRepository {
  Future<Either<Failure, void>> saveScan(SaveRequest request);
}

class ScannerRepositoryImpl implements ScannerRepository {
  final ScannerRemoteDataSource remoteDataSource;
  
  ScannerRepositoryImpl(this.remoteDataSource);
  
  @override
  Future<Either<Failure, void>> saveScan(SaveRequest request) async {
    try {
      await remoteDataSource.saveScan(request);
      return const Right(null);
    } catch (e) {
      return Left(ServerFailure(e.toString()));
    }
  }
}
```

## Data Source
```dart
abstract class ScannerRemoteDataSource {
  Future<void> saveScan(SaveRequest request);
}

class ScannerRemoteDataSourceImpl implements ScannerRemoteDataSource {
  final ApiClient apiClient;
  
  ScannerRemoteDataSourceImpl(this.apiClient);
  
  @override
  Future<void> saveScan(SaveRequest request) async {
    final response = await apiClient.post(
      '/api/scans',
      data: request.toJson(),
    );
    
    if (response.statusCode != 200) {
      throw ServerException('Failed to save scan');
    }
  }
}
```

## Widget Structure

### Home Page
```dart
class HomePage extends ConsumerWidget {
  Widget build(BuildContext context, WidgetRef ref) {
    return Scaffold(
      body: Column(
        children: [
          // Barcode Scanner (top half)
          Expanded(
            flex: 1,
            child: BarcodeScannerWidget(),
          ),
          
          // Scan Result Display
          ScanResultDisplay(),
          
          // History List (bottom half)  
          Expanded(
            flex: 1,
            child: ScanHistoryList(),
          ),
        ],
      ),
    );
  }
}
```

### Detail Page with Save API Call
```dart
class DetailPage extends ConsumerWidget {
  final String barcode;
  
  Widget build(BuildContext context, WidgetRef ref) {
    final formState = ref.watch(formProvider);
    
    return Scaffold(
      appBar: AppBar(title: Text('Edit Details')),
      body: Column(
        children: [
          // Barcode Header
          Container(
            padding: EdgeInsets.all(16),
            child: Text('Barcode: $barcode'),
          ),
          
          // 4 Text Fields
          Expanded(
            child: Padding(
              padding: EdgeInsets.all(16),
              child: Column(
                children: [
                  TextField(
                    decoration: InputDecoration(labelText: 'Field 1'),
                    onChanged: (value) => ref.read(formProvider.notifier).updateField1(value),
                  ),
                  TextField(
                    decoration: InputDecoration(labelText: 'Field 2'),
                    onChanged: (value) => ref.read(formProvider.notifier).updateField2(value),
                  ),
                  TextField(
                    decoration: InputDecoration(labelText: 'Field 3'),
                    onChanged: (value) => ref.read(formProvider.notifier).updateField3(value),
                  ),
                  TextField(
                    decoration: InputDecoration(labelText: 'Field 4'),
                    onChanged: (value) => ref.read(formProvider.notifier).updateField4(value),
                  ),
                ],
              ),
            ),
          ),
          
          // Error Message
          if (formState.error != null)
            Container(
              padding: EdgeInsets.all(16),
              child: Text(
                formState.error!,
                style: TextStyle(color: Colors.red),
              ),
            ),
          
          // Save & Print Buttons
          Padding(
            padding: EdgeInsets.all(16),
            child: Row(
              children: [
                Expanded(
                  child: ElevatedButton(
                    onPressed: formState.isLoading ? null : () => _saveData(ref),
                    child: formState.isLoading 
                      ? CircularProgressIndicator()
                      : Text('Save'),
                  ),
                ),
                SizedBox(width: 16),
                Expanded(
                  child: ElevatedButton(
                    onPressed: _printData,  
                    child: Text('Print'),
                  ),
                ),
              ],
            ),
          ),
        ],
      ),
    );
  }
  
  void _saveData(WidgetRef ref) async {
    final formState = ref.read(formProvider);
    final saveRequest = SaveRequest(
      barcode: barcode,
      field1: formState.field1,
      field2: formState.field2,
      field3: formState.field3,
      field4: formState.field4,
    );
    
    await ref.read(formProvider.notifier).saveData(saveRequest);
  }
}
```

## Core Functions

### Save Data with API Call
```dart
class FormNotifier extends StateNotifier<FormState> {
  final SaveScanUseCase saveScanUseCase;
  
  FormNotifier(this.saveScanUseCase, String barcode) 
    : super(FormState(barcode: barcode));
  
  Future<void> saveData(SaveRequest request) async {
    state = state.copyWith(isLoading: true, error: null);
    
    final result = await saveScanUseCase(request);
    
    result.fold(
      (failure) => state = state.copyWith(
        isLoading: false, 
        error: failure.message,
      ),
      (_) {
        state = state.copyWith(isLoading: false);
        // Save to local storage after successful API call
        _saveToLocal(request);
        // Navigate back or show success message
      },
    );
  }
  
  void _saveToLocal(SaveRequest request) {
    // Save to Hive local storage
    final scanItem = ScanItem(
      barcode: request.barcode,
      timestamp: DateTime.now(),
      field1: request.field1,
      field2: request.field2,
      field3: request.field3,
      field4: request.field4,
    );
    // Add to Hive box
  }
}
```

### Print Data
```dart
void printData(ScanItem item) {
  // Format data for printing
  // Use platform printing service
}
```

## Dependencies
```yaml
dependencies:
  flutter_riverpod: ^2.4.9
  mobile_scanner: ^4.0.1
  hive: ^2.2.3
  hive_flutter: ^1.1.0
  go_router: ^12.1.3
  dio: ^5.3.2
  dartz: ^0.10.1
  get_it: ^7.6.4
  
dev_dependencies:
  hive_generator: ^2.0.1
  build_runner: ^2.4.7
```

## Error Handling
```dart
abstract class Failure {
  final String message;
  const Failure(this.message);
}

class ServerFailure extends Failure {
  const ServerFailure(String message) : super(message);
}

class NetworkFailure extends Failure {
  const NetworkFailure(String message) : super(message);
}
```

## Key Points
- Save button calls API to save form data
- Show loading state during API call
- Handle API errors with user-friendly messages
- Save to local storage only after successful API call
- Use clean architecture with use cases and repository pattern
- Keep UI simple with proper error handling