Sales History

lib/features/sales_history/
├── screens/
│   └── sales_history_screen.dart        # Main UI screen
├── providers/
│   └── sales_history_provider.dart      # State management (planned)
├── models/
│   ├── sale_transaction.dart            # Transaction model (planned)
│   └── sale_item.dart                   # Line item model (planned)
└── widgets/
    ├── transaction_card.dart            # Display widget (planned)
    ├── sales_chart.dart                 # Visualization widget (planned)
    └── date_filter.dart                 # Date range selector (planned)

class SaleTransaction {
  final String id;
  final DateTime timestamp;
  
  final List<SaleItem> items;
  final double subtotal;
  final double discountAmount;
  final double taxAmount;
  final double totalAmount;
  
  final String paymentMethod;
  final String? customerName;
  final String? notes;
  
  // Computed properties
  int get itemCount => items.length;
  double get totalQuantity => items.fold(0, (sum, item) => sum + item.quantity);
}

class SaleItem {
  final String productId;
  final String productName;
  final int quantity;
  final double unitPrice;
  final double lineTotal;
  final double? discount;
}

class SalesHistoryProvider extends ChangeNotifier {
  final SharedPreferences _prefs;
  List<SaleTransaction> _transactions = [];
  
  // CRUD operations
  Future<void> recordSale(SaleTransaction sale) async { ... }
  Future<void> deleteSale(String id) async { ... }
  
  // Queries
  List<SaleTransaction> getSalesByDateRange(DateTime start, DateTime end) { ... }
  List<SaleTransaction> getSalesForProduct(String productId) { ... }
  
  // Analytics
  double getTotalRevenue(DateTime start, DateTime end) { ... }
  int getTransactionCount(DateTime start, DateTime end) { ... }
  double getAverageSale(DateTime start, DateTime end) { ... }
  Map<String, double> getProductSalesBreakdown() { ... }
}

📊 Line Chart    → Daily revenue trend over time
📊 Bar Chart     → Sales by product category
📊 Pie Chart     → Payment method breakdown
📊 Area Chart    → Cumulative revenue growth