worker/CART_API_QUICK_START.md

# Cart API Integration - Quick Start Guide

## Files Created

### Core Files (Ready to Use)
1. `/Users/ssg/project/worker/lib/core/constants/api_constants.dart` - Updated with cart endpoints
2. `/Users/ssg/project/worker/lib/features/cart/domain/repositories/cart_repository.dart` - Repository interface
3. `/Users/ssg/project/worker/lib/features/cart/data/datasources/cart_remote_datasource.dart` - API calls
4. `/Users/ssg/project/worker/lib/features/cart/data/datasources/cart_local_datasource.dart` - Hive storage
5. `/Users/ssg/project/worker/lib/features/cart/data/repositories/cart_repository_impl.dart` - Implementation

### Generated Files (Riverpod)
6. `/Users/ssg/project/worker/lib/features/cart/data/datasources/cart_remote_datasource.g.dart`
7. `/Users/ssg/project/worker/lib/features/cart/data/datasources/cart_local_datasource.g.dart`
8. `/Users/ssg/project/worker/lib/features/cart/data/repositories/cart_repository_impl.g.dart`

### Documentation
9. `/Users/ssg/project/worker/lib/features/cart/CART_API_INTEGRATION.md` - Detailed docs
10. `/Users/ssg/project/worker/CART_API_INTEGRATION_SUMMARY.md` - Complete summary
11. `/Users/ssg/project/worker/CART_API_QUICK_START.md` - This file

## Quick Usage

### 1. Import the Repository

```dart
import 'package:worker/features/cart/data/repositories/cart_repository_impl.dart';
import 'package:worker/features/cart/domain/entities/cart_item.dart';
```

### 2. Use in Your Provider

```dart
@riverpod
class Cart extends _$Cart {
  CartRepository get _repository => ref.read(cartRepositoryProvider);

  // Add to cart
  Future<void> addProductToCart(Product product, double quantity) async {
    try {
      final items = await _repository.addToCart(
        itemIds: [product.erpnextItemCode ?? product.productId],
        quantities: [quantity],
        prices: [product.basePrice],
      );
      // Update UI state with items
    } catch (e) {
      // Show error
    }
  }

  // Get cart items
  Future<void> loadCart() async {
    try {
      final items = await _repository.getCartItems();
      // Update UI state with items
    } catch (e) {
      // Show error
    }
  }

  // Remove from cart
  Future<void> removeProduct(String itemId) async {
    try {
      await _repository.removeFromCart(itemIds: [itemId]);
      // Update UI state
    } catch (e) {
      // Show error
    }
  }
}
```

## API Methods Available

```dart
// Add items to cart (replaces/updates existing)
Future<List<CartItem>> addToCart({
  required List<String> itemIds,      // ERPNext item codes
  required List<double> quantities,
  required List<double> prices,
});

// Remove items from cart
Future<bool> removeFromCart({
  required List<String> itemIds,
});

// Get all cart items
Future<List<CartItem>> getCartItems();

// Update quantity (uses addToCart internally)
Future<List<CartItem>> updateQuantity({
  required String itemId,
  required double quantity,
  required double price,
});

// Clear entire cart
Future<bool> clearCart();

// Get cart total
Future<double> getCartTotal();

// Get cart item count
Future<int> getCartItemCount();
```

## Error Handling

All methods can throw:
- `NoInternetException` - No network connection
- `TimeoutException` - Request timeout
- `UnauthorizedException` - 401 auth error
- `ForbiddenException` - 403 permission error
- `NotFoundException` - 404 not found
- `ServerException` - 5xx server error
- `NetworkException` - Other network errors
- `StorageException` - Local storage error
- `ValidationException` - Invalid input
- `UnknownException` - Unexpected error

## Important Notes

### Product ID Mapping
```dart
// ALWAYS use erpnextItemCode for API calls
final itemId = product.erpnextItemCode ?? product.productId;

await _repository.addToCart(
  itemIds: [itemId],  // ERPNext code, not UUID
  quantities: [quantity],
  prices: [product.basePrice],
);
```

### Offline Support
- Read operations fallback to local storage when offline
- Write operations save locally and queue for sync (TODO)
- Cart persists across app restarts

### Response Format
Methods return domain `CartItem` entities:
```dart
class CartItem {
  final String cartItemId;
  final String cartId;
  final String productId;      // ERPNext item code
  final double quantity;
  final double unitPrice;
  final double subtotal;
  final DateTime addedAt;
}
```

## Common Patterns

### Add Product to Cart
```dart
void onAddToCart(Product product) async {
  try {
    setState(() => _isLoading = true);

    await _repository.addToCart(
      itemIds: [product.erpnextItemCode ?? product.productId],
      quantities: [1.0],
      prices: [product.basePrice],
    );

    // Show success
    ScaffoldMessenger.of(context).showSnackBar(
      SnackBar(content: Text('Added to cart')),
    );
  } catch (e) {
    // Show error
    ScaffoldMessenger.of(context).showSnackBar(
      SnackBar(content: Text('Failed to add to cart')),
    );
  } finally {
    setState(() => _isLoading = false);
  }
}
```

### Load Cart on Page Open
```dart
@override
void initState() {
  super.initState();
  _loadCart();
}

Future<void> _loadCart() async {
  try {
    final items = await ref.read(cartRepositoryProvider).getCartItems();
    // Update state
  } catch (e) {
    // Handle error
  }
}
```

### Update Quantity
```dart
Future<void> onQuantityChanged(String itemId, double newQuantity, double price) async {
  try {
    await _repository.updateQuantity(
      itemId: itemId,
      quantity: newQuantity,
      price: price,
    );
    // Reload cart
    await loadCart();
  } catch (e) {
    // Show error
  }
}
```

### Remove Item
```dart
Future<void> onRemoveItem(String itemId) async {
  try {
    await _repository.removeFromCart(itemIds: [itemId]);
    // Reload cart
    await loadCart();
  } catch (e) {
    // Show error
  }
}
```

## Testing

Run tests with:
```bash
flutter test
```

Test files location:
- `/Users/ssg/project/worker/test/features/cart/`

## Troubleshooting

### Issue: "Box is already open and of type Box<dynamic>"
**Solution**: The datasource already uses `Box<dynamic>`. Don't re-open boxes with specific types.

### Issue: "Network error" on every request
**Solution**: Check if user is authenticated. Cart endpoints require valid session.

### Issue: Items not syncing to API
**Solution**: Check network connection. Items save locally when offline.

### Issue: "ProductId not found in cart"
**Solution**: Use ERPNext item code, not product UUID. Check `product.erpnextItemCode`.

## Next Steps

1. Update existing `cart_provider.dart` to use repository
2. Add loading states to cart UI
3. Add error messages with SnackBar
4. Test all cart operations
5. Implement offline queue (optional)

## Support

For questions or issues:
- Check `/Users/ssg/project/worker/lib/features/cart/CART_API_INTEGRATION.md` for detailed docs
- Check `/Users/ssg/project/worker/CART_API_INTEGRATION_SUMMARY.md` for architecture overview
- Review code comments in source files