second commit

lib/domain/entities/product.dart

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+import 'package:equatable/equatable.dart';
+
+import '../../core/constants/app_constants.dart';
+
+/// Merchandise categories shown as filter chips on the POS dashboard.
+enum ProductCategory {
+  dairy('Dairy', '🥛'),
+  grocery('Grocery', '🛒'),
+  fruits('Fruits', '🍎'),
+  vegetables('Vegetables', '🥦'),
+  beverages('Beverages', '🥤'),
+  snacks('Snacks', '🍪'),
+  personalCare('Personal Care', '🧴'),
+  household('Household', '🏠');
+
+  const ProductCategory(this.label, this.emoji);
+
+  final String label;
+  final String emoji;
+}
+
+/// Unit of measure — drives whether fractional quantities are permitted.
+enum UnitOfMeasure {
+  piece('pc'),
+  kilogram('kg'),
+  gram('g'),
+  litre('L'),
+  millilitre('ml'),
+  pack('pack');
+
+  const UnitOfMeasure(this.symbol);
+
+  final String symbol;
+
+  bool get allowsFractional =>
+      this == UnitOfMeasure.kilogram || this == UnitOfMeasure.litre;
+}
+
+/// A sellable item in the catalogue.
+class Product extends Equatable {
+  const Product({
+    required this.id,
+    required this.name,
+    required this.barcode,
+    required this.sku,
+    required this.category,
+    required this.price,
+    required this.stock,
+    this.mrp,
+    this.emoji = '📦',
+    this.imageUrl,
+    this.unit = UnitOfMeasure.piece,
+    this.gstRate = AppConstants.defaultGstRate,
+    this.brand,
+    this.isActive = true,
+  });
+
+  final String id;
+  final String name;
+  final String barcode;
+  final String sku;
+  final ProductCategory category;
+
+  /// Selling price per [unit], inclusive of GST (Indian retail convention).
+  final double price;
+
+  /// Printed maximum retail price, used to display savings.
+  final double? mrp;
+
+  final double stock;
+  final String emoji;
+  final String? imageUrl;
+  final UnitOfMeasure unit;
+  final double gstRate;
+  final String? brand;
+  final bool isActive;
+
+  bool get isOutOfStock => stock <= 0;
+  bool get isLowStock =>
+      stock > 0 && stock <= AppConstants.lowStockThreshold;
+
+  bool get hasDiscount => mrp != null && mrp! > price;
+
+  double get savings => hasDiscount ? (mrp! - price) : 0;
+
+  double get discountPercent =>
+      hasDiscount ? ((mrp! - price) / mrp!) * 100 : 0;
+
+  /// Price stripped of embedded GST — the taxable value.
+  double get netPrice => price / (1 + gstRate);
+
+  /// GST rupees embedded inside [price].
+  double get taxPerUnit => price - netPrice;
+
+  /// Fuzzy match used by the search bar across name, barcode, SKU and brand.
+  bool matches(String query) {
+    final q = query.trim().toLowerCase();
+    if (q.isEmpty) return true;
+    return name.toLowerCase().contains(q) ||
+        barcode.toLowerCase().contains(q) ||
+        sku.toLowerCase().contains(q) ||
+        (brand?.toLowerCase().contains(q) ?? false) ||
+        category.label.toLowerCase().contains(q);
+  }
+
+  Product copyWith({
+    String? name,
+    double? price,
+    double? mrp,
+    double? stock,
+    ProductCategory? category,
+    bool? isActive,
+  }) {
+    return Product(
+      id: id,
+      name: name ?? this.name,
+      barcode: barcode,
+      sku: sku,
+      category: category ?? this.category,
+      price: price ?? this.price,
+      mrp: mrp ?? this.mrp,
+      stock: stock ?? this.stock,
+      emoji: emoji,
+      imageUrl: imageUrl,
+      unit: unit,
+      gstRate: gstRate,
+      brand: brand,
+      isActive: isActive ?? this.isActive,
+    );
+  }
+
+  @override
+  List<Object?> get props => [id, name, barcode, sku, price, stock, isActive];
+}