add cart

lib/features/cart/presentation/providers/cart_state.dart

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+/// Cart State
+///
+/// Immutable state class for cart management.
+library;
+
+import 'package:worker/features/products/domain/entities/product.dart';
+
+/// Cart Item Data
+///
+/// Represents a product in the cart with quantity.
+class CartItemData {
+  final Product product;
+  final double quantity;
+
+  const CartItemData({
+    required this.product,
+    required this.quantity,
+  });
+
+  /// Calculate line total
+  double get lineTotal => product.basePrice * quantity;
+
+  CartItemData copyWith({
+    Product? product,
+    double? quantity,
+  }) {
+    return CartItemData(
+      product: product ?? this.product,
+      quantity: quantity ?? this.quantity,
+    );
+  }
+}
+
+/// Cart State
+///
+/// Represents the complete state of the shopping cart.
+class CartState {
+  final List<CartItemData> items;
+  final String selectedWarehouse;
+  final String? discountCode;
+  final bool discountCodeApplied;
+  final String memberTier;
+  final double memberDiscountPercent;
+  final double subtotal;
+  final double memberDiscount;
+  final double shippingFee;
+  final double total;
+
+  const CartState({
+    required this.items,
+    required this.selectedWarehouse,
+    this.discountCode,
+    required this.discountCodeApplied,
+    required this.memberTier,
+    required this.memberDiscountPercent,
+    required this.subtotal,
+    required this.memberDiscount,
+    required this.shippingFee,
+    required this.total,
+  });
+
+  factory CartState.initial() {
+    return const CartState(
+      items: [],
+      selectedWarehouse: 'Kho Hà Nội - Nguyễn Trãi',
+      discountCode: null,
+      discountCodeApplied: false,
+      memberTier: '',
+      memberDiscountPercent: 0.0,
+      subtotal: 0.0,
+      memberDiscount: 0.0,
+      shippingFee: 0.0,
+      total: 0.0,
+    );
+  }
+
+  bool get isEmpty => items.isEmpty;
+  bool get isNotEmpty => items.isNotEmpty;
+  int get itemCount => items.length;
+
+  /// Get total quantity across all items
+  double get totalQuantity {
+    return items.fold<double>(0.0, (sum, item) => sum + item.quantity);
+  }
+
+  CartState copyWith({
+    List<CartItemData>? items,
+    String? selectedWarehouse,
+    String? discountCode,
+    bool? discountCodeApplied,
+    String? memberTier,
+    double? memberDiscountPercent,
+    double? subtotal,
+    double? memberDiscount,
+    double? shippingFee,
+    double? total,
+  }) {
+    return CartState(
+      items: items ?? this.items,
+      selectedWarehouse: selectedWarehouse ?? this.selectedWarehouse,
+      discountCode: discountCode ?? this.discountCode,
+      discountCodeApplied: discountCodeApplied ?? this.discountCodeApplied,
+      memberTier: memberTier ?? this.memberTier,
+      memberDiscountPercent: memberDiscountPercent ?? this.memberDiscountPercent,
+      subtotal: subtotal ?? this.subtotal,
+      memberDiscount: memberDiscount ?? this.memberDiscount,
+      shippingFee: shippingFee ?? this.shippingFee,
+      total: total ?? this.total,
+    );
+  }
+}