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test/unit/cart_test.dart

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+import 'package:flutter_test/flutter_test.dart';
+import 'package:nearle_pos/domain/entities/cart.dart';
+import 'package:nearle_pos/domain/entities/customer.dart';
+import 'package:nearle_pos/domain/entities/product.dart';
+
+/// Plain 18% GST item priced at a round number so expected values stay exact.
+const _item = Product(
+  id: 'test-1',
+  name: 'Test Item',
+  barcode: '8900000000001',
+  sku: 'TST-001',
+  category: ProductCategory.grocery,
+  price: 100,
+  stock: 50,
+  gstRate: 0.18,
+);
+
+Customer _silver() => Customer(
+      id: 'cust-1',
+      name: 'Silver Shopper',
+      mobile: '9876543210',
+      loyaltyPoints: 320,
+      // Above the 10,000 silver threshold, below the 50,000 gold one.
+      lifetimeSpend: 24500,
+    );
+
+void main() {
+  group('Discount', () {
+    test('percentage resolves against the base', () {
+      const d = Discount(type: DiscountType.percentage, value: 10);
+      expect(d.amountOn(200), 20);
+    });
+
+    test('flat discount never exceeds the base', () {
+      const d = Discount(type: DiscountType.flat, value: 500);
+      expect(d.amountOn(200), 200);
+    });
+
+    test('none is inactive and worth nothing', () {
+      expect(Discount.none.isActive, isFalse);
+      expect(Discount.none.amountOn(200), 0);
+    });
+  });
+
+  group('CartLine', () {
+    test('splits GST out of a tax-inclusive price', () {
+      const line = CartLine(product: _item, quantity: 2);
+
+      expect(line.grossAmount, 200);
+      expect(line.payable, 200);
+      // 200 / 1.18 = 169.4915... -> 169.49
+      expect(line.taxableValue, 169.49);
+      expect(line.taxAmount, 30.51);
+      expect(line.cgst + line.sgst, closeTo(line.taxAmount, 0.01));
+    });
+
+    test('line discount reduces the payable', () {
+      const line = CartLine(
+        product: _item,
+        quantity: 2,
+        discount: Discount(type: DiscountType.percentage, value: 10),
+      );
+
+      expect(line.discountAmount, 20);
+      expect(line.payable, 180);
+    });
+
+    test('flags a quantity beyond available stock', () {
+      const ok = CartLine(product: _item, quantity: 50);
+      const over = CartLine(product: _item, quantity: 51);
+
+      expect(ok.exceedsStock, isFalse);
+      expect(over.exceedsStock, isTrue);
+    });
+  });
+
+  group('Cart totals', () {
+    test('empty cart is all zeroes', () {
+      const cart = Cart.empty;
+
+      expect(cart.isEmpty, isTrue);
+      expect(cart.subtotal, 0);
+      expect(cart.grandTotal, 0);
+      expect(cart.pointsEarned, 0);
+    });
+
+    test('sums lines into a subtotal', () {
+      const cart = Cart(lines: [CartLine(product: _item, quantity: 2)]);
+
+      expect(cart.lineCount, 1);
+      expect(cart.totalQuantity, 2);
+      expect(cart.subtotal, 200);
+      expect(cart.grandTotal, 200);
+      expect(cart.roundOff, 0);
+    });
+
+    test('rounds the payable to the nearest rupee', () {
+      const odd = Product(
+        id: 'test-2',
+        name: 'Odd Price',
+        barcode: '8900000000002',
+        sku: 'TST-002',
+        category: ProductCategory.grocery,
+        price: 99.99,
+        stock: 10,
+      );
+      const cart = Cart(lines: [CartLine(product: odd, quantity: 1)]);
+
+      expect(cart.netAmount, 99.99);
+      expect(cart.grandTotal, 100);
+      expect(cart.roundOff, closeTo(0.01, 0.001));
+    });
+
+    test('applies the membership discount automatically', () {
+      final cart = Cart(
+        lines: const [CartLine(product: _item, quantity: 2)],
+        customer: _silver(),
+      );
+
+      expect(cart.customer!.tier, MembershipTier.silver);
+      // Silver is 2% off 200.
+      expect(cart.membershipDiscountAmount, 4);
+      expect(cart.netAmount, 196);
+      expect(cart.grandTotal, 196);
+    });
+
+    test('walk-in bills get no membership discount', () {
+      const cart = Cart(lines: [CartLine(product: _item, quantity: 2)]);
+
+      expect(cart.isWalkIn, isTrue);
+      expect(cart.membershipDiscountAmount, 0);
+      expect(cart.grandTotal, 200);
+    });
+
+    test('stacks a manual discount on top of the membership one', () {
+      final cart = Cart(
+        lines: const [CartLine(product: _item, quantity: 2)],
+        customer: _silver(),
+        billDiscount: const Discount(type: DiscountType.flat, value: 16),
+      );
+
+      // 4 (silver) + 16 (manual) = 20 off 200.
+      expect(cart.billDiscountTotal, 20);
+      expect(cart.grandTotal, 180);
+    });
+
+    test('apportions bill-level discounts across the GST charged', () {
+      final full = Cart(
+        lines: const [CartLine(product: _item, quantity: 2)],
+        customer: _silver(),
+      );
+
+      // Bill fell to 98% of subtotal, so GST should fall in step.
+      expect(full.taxAmount, closeTo(30.51 * 0.98, 0.02));
+      expect(full.taxableAmount, closeTo(full.netAmount - full.taxAmount, 0.01));
+    });
+
+    test('breaks GST out by slab', () {
+      const zeroRated = Product(
+        id: 'test-3',
+        name: 'Onion 1kg',
+        barcode: '8900000000003',
+        sku: 'TST-003',
+        category: ProductCategory.vegetables,
+        price: 35,
+        stock: 20,
+        gstRate: 0,
+      );
+      const cart = Cart(lines: [
+        CartLine(product: _item, quantity: 1),
+        CartLine(product: zeroRated, quantity: 1),
+      ]);
+
+      final breakdown = cart.taxBreakdown;
+      expect(breakdown.keys, containsAll<double>([0.18, 0.0]));
+      expect(breakdown[0.0], 0);
+      expect(breakdown[0.18]!, greaterThan(0));
+    });
+  });
+
+  group('Loyalty', () {
+    test('earns one point per ten rupees, floored', () {
+      final cart = Cart(
+        lines: const [CartLine(product: _item, quantity: 2)],
+        customer: _silver(),
+      );
+
+      // Grand total 196 -> 19 points.
+      expect(cart.grandTotal, 196);
+      expect(cart.pointsEarned, 19);
+    });
+
+    test('caps redemption at the point balance', () {
+      final cart = Cart(
+        lines: const [CartLine(product: _item, quantity: 2)],
+        customer: _silver(),
+      );
+
+      // 320 points held; the bill could absorb far more.
+      expect(cart.maxRedeemablePoints, 320);
+    });
+
+    test('redeemed points come off the payable at 25 paise each', () {
+      final cart = Cart(
+        lines: const [CartLine(product: _item, quantity: 2)],
+        customer: _silver(),
+        pointsRedeemed: 320,
+      );
+
+      expect(cart.loyaltyRedemptionValue, 80);
+      // 200 - 4 (silver) - 80 (points) = 116.
+      expect(cart.netAmount, 116);
+      expect(cart.grandTotal, 116);
+    });
+
+    test('a walk-in can never redeem', () {
+      const cart = Cart(lines: [CartLine(product: _item, quantity: 2)]);
+      expect(cart.maxRedeemablePoints, 0);
+    });
+
+    test('the payable can never go below zero', () {
+      final cart = Cart(
+        lines: const [CartLine(product: _item, quantity: 1)],
+        customer: _silver(),
+        billDiscount: const Discount(type: DiscountType.flat, value: 9999),
+      );
+
+      expect(cart.netAmount, 0);
+      expect(cart.grandTotal, 0);
+    });
+  });
+
+  group('MembershipTier', () {
+    test('maps lifetime spend onto the right tier', () {
+      expect(MembershipTier.forSpend(0), MembershipTier.bronze);
+      expect(MembershipTier.forSpend(9999), MembershipTier.bronze);
+      expect(MembershipTier.forSpend(10000), MembershipTier.silver);
+      expect(MembershipTier.forSpend(50000), MembershipTier.gold);
+      expect(MembershipTier.forSpend(150000), MembershipTier.platinum);
+      expect(MembershipTier.forSpend(999999), MembershipTier.platinum);
+    });
+
+    test('platinum is the ceiling', () {
+      expect(MembershipTier.platinum.next, isNull);
+      expect(MembershipTier.bronze.next, MembershipTier.silver);
+    });
+  });
+}