feat: dukung penjualan produk per timbangan

Produk kini punya cara jual `unit` (cacah) atau `weight` (timbangan),
mengikuti kontrak backend di docs/integration-weight-based-products.md.

- tipe SellBy, domain/infrastructure unit baru, dan endpoint /api/v1/units
- dialog input berat saat produk timbangan ditambahkan ke keranjang
- tiap penimbangan jadi baris keranjang sendiri; total baris dihitung
  berat x harga satuan, sedangkan produk cacah tetap digabung
- request ke backend mengirim quantity 1 dan membawa berat
- migrasi DB v3: kolom sell_by, unit_id, unit_name, unit_abbreviation
  di tabel products supaya satuan tetap tampil saat offline
- tampilan keranjang, struk, split bill, void, dan refund memakai berat
- test/weight_based_products_test.dart menutup perilaku di atas (9 test)

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

lib/application/checkout/checkout_form/checkout_form_bloc.dart

@@ -3,6 +3,7 @@ import 'dart:developer';
 import 'package:bloc/bloc.dart';
 import 'package:freezed_annotation/freezed_annotation.dart';
 import 'package:injectable/injectable.dart' hide Order;
+import 'package:uuid/uuid.dart';
 
 import '../../../common/types/order_type.dart';
 import '../../../domain/delivery/delivery.dart';
@@ -19,6 +20,33 @@ class CheckoutFormBloc extends Bloc<CheckoutFormEvent, CheckoutFormState> {
   CheckoutFormBloc() : super(CheckoutFormState.initial()) {
     on<CheckoutFormEvent>(_onCheckoutFormEvent);
   }
+
+  /// Baris berbobot dihitung `weight × harga`, baris cacah `quantity × harga`.
+  /// Satu tempat saja supaya total keranjang, subtotal, dan ringkasan tidak
+  /// pernah berbeda hitungan.
+  CheckoutFormState _recalculate(
+    CheckoutFormState state,
+    List<ProductQuantity> items,
+  ) {
+    final totalQuantity = items.fold<int>(
+      0,
+      // Baris berbobot selalu satu penimbangan, jadi dihitung satu.
+      (sum, item) => sum + (item.isWeighted ? 1 : item.quantity),
+    );
+
+    final totalPrice = items.fold<double>(
+      0,
+      (sum, item) => sum + item.lineTotal,
+    );
+
+    return state.copyWith(
+      items: items,
+      totalQuantity: totalQuantity,
+      totalPrice: totalPrice.toInt(),
+      isLoading: false,
+    );
+  }
+
   Future<void> _onCheckoutFormEvent(
     CheckoutFormEvent event,
     Emitter<CheckoutFormState> emit,
@@ -26,12 +54,21 @@ class CheckoutFormBloc extends Bloc<CheckoutFormEvent, CheckoutFormState> {
     return event.map(
       addItem: (e) async {
         final currentState = state;
+
+        // Produk timbangan tidak punya stepper — masuk lewat addWeightedItem
+        // setelah kasir memasukkan angka timbangan.
+        if (e.product.isSoldByWeight) {
+          log('⚖️ ${e.product.name} dijual per timbangan, butuh berat');
+          return;
+        }
+
         emit(currentState.copyWith(isLoading: true));
 
         List<ProductQuantity> items = [...currentState.items];
 
         final index = items.indexWhere(
           (element) =>
+              !element.isWeighted &&
               element.product.id == e.product.id &&
               element.variant?.id == e.variant?.id,
         );
@@ -49,35 +86,47 @@ class CheckoutFormBloc extends Bloc<CheckoutFormEvent, CheckoutFormState> {
               quantity: 1,
               variant: e.variant,
               notes: '',
+              lineId: const Uuid().v4(),
             ),
           );
         }
 
         log('🛒 Items updated: ${items.length} items total ${items.toList()}');
 
-        final totalQuantity = items.fold<int>(
-          0,
-          (sum, item) => sum + item.quantity,
-        );
+        emit(_recalculate(currentState, items));
+      },
+      addWeightedItem: (e) async {
+        final currentState = state;
+        emit(currentState.copyWith(isLoading: true));
 
-        final totalPrice = state.items.isEmpty
-            ? 0.0
-            : state.items
-                  .map(
-                    (e) =>
-                        (e.product.price * e.quantity) +
-                        (e.variant?.priceModifier ?? 0),
-                  )
-                  .reduce((value, element) => value + element);
-
-        emit(
-          currentState.copyWith(
-            items: items,
-            totalQuantity: totalQuantity,
-            totalPrice: totalPrice.toInt(),
-            isLoading: false,
+        // Sengaja tidak digabung dengan baris lain: dua penimbangan adalah dua
+        // ikan berbeda, masing-masing bisa di-void atau dibayar terpisah.
+        final items = [
+          ...currentState.items,
+          ProductQuantity(
+            product: e.product,
+            variant: e.variant,
+            quantity: 1,
+            notes: '',
+            lineId: const Uuid().v4(),
+            weight: e.weight,
           ),
-        );
+        ];
+
+        log('⚖️ Penimbangan baru: ${e.product.name} ${e.weight}');
+
+        emit(_recalculate(currentState, items));
+      },
+      updateItemWeight: (e) async {
+        final currentState = state;
+        final items = [...currentState.items];
+
+        final index = items.indexWhere((item) => item.lineId == e.lineId);
+        if (index == -1) return;
+
+        items[index] = items[index].copyWith(weight: e.weight);
+
+        emit(_recalculate(currentState, items));
       },
       removeItem: (e) async {
         final currentState = state;
@@ -86,6 +135,7 @@ class CheckoutFormBloc extends Bloc<CheckoutFormEvent, CheckoutFormState> {
 
         final index = items.indexWhere(
           (element) =>
+              !element.isWeighted &&
               element.product.id == e.product.id &&
               element.variant?.id == e.variant?.id,
         );
@@ -103,32 +153,18 @@ class CheckoutFormBloc extends Bloc<CheckoutFormEvent, CheckoutFormState> {
           }
         }
 
-        final totalQuantity = items.fold<int>(
-          0,
-          (sum, item) => sum + item.quantity,
-        );
-        final totalPrice = items.fold<int>(
-          0,
-          (sum, item) =>
-              sum +
-              (item.quantity *
-                  (item.variant?.priceModifier.toInt() ??
-                      item.product.price.toInt())),
-        );
+        log('🗑️ Item removed. Total items: ${items.length}');
 
-        log(
-          '🗑️ Item removed. Total items: ${items.length}, totalQuantity: $totalQuantity, totalPrice: $totalPrice',
-        );
+        emit(_recalculate(currentState, items));
+      },
+      removeLine: (e) async {
+        final currentState = state;
+        final items = [...currentState.items]
+          ..removeWhere((item) => item.lineId == e.lineId);
 
-        // Emit state baru
-        emit(
-          currentState.copyWith(
-            items: items,
-            totalQuantity: totalQuantity,
-            totalPrice: totalPrice,
-            isLoading: false,
-          ),
-        );
+        log('🗑️ Baris dihapus. Sisa ${items.length} baris');
+
+        emit(_recalculate(currentState, items));
       },
       started: (e) async {
         emit(CheckoutFormState.initial().copyWith(isLoading: true));
@@ -153,14 +189,13 @@ class CheckoutFormBloc extends Bloc<CheckoutFormEvent, CheckoutFormState> {
           );
         }
       },
-      updateItemNotes: (e) async {
+      updateLineNotes: (e) async {
         final currentState = state;
 
-        // Clone list items agar tidak mutasi langsung
+        // Catatan diikat ke baris, bukan ke produk: dua penimbangan produk yang
+        // sama bisa punya catatan berbeda.
         final items = [...currentState.items];
-        final index = items.indexWhere(
-          (element) => element.product.id == e.product.id,
-        );
+        final index = items.indexWhere((item) => item.lineId == e.lineId);
 
         if (index != -1) {
           items[index] = items[index].copyWith(notes: e.notes);
@@ -181,8 +216,8 @@ class CheckoutFormBloc extends Bloc<CheckoutFormEvent, CheckoutFormState> {
         emit(state.copyWith(orderAdded: e.order));
       },
       customerNameChanged: (e) async {
-        emit(state.copyWith(customerName: e.name,));
-      }
+        emit(state.copyWith(customerName: e.name));
+      },
     );
   }
 }

lib/application/checkout/checkout_form/checkout_form_event.dart

@@ -10,15 +10,32 @@ class CheckoutFormEvent with _$CheckoutFormEvent {
     ProductVariant? variant,
   ) = _AddItem;
 
+  /// Satu penimbangan = satu baris baru. Dipanggil setiap kali kasir selesai
+  /// memasukkan angka timbangan, meski produknya sama dengan baris lain.
+  const factory CheckoutFormEvent.addWeightedItem(
+    Product product,
+    ProductVariant? variant,
+    double weight,
+  ) = _AddWeightedItem;
+
+  /// Koreksi angka timbangan pada satu baris tertentu.
+  const factory CheckoutFormEvent.updateItemWeight(
+    String lineId,
+    double weight,
+  ) = _UpdateItemWeight;
+
   const factory CheckoutFormEvent.removeItem(
     Product product,
     ProductVariant? variant,
   ) = _RemoveItem;
 
-  const factory CheckoutFormEvent.updateItemNotes(
-    Product product,
+  /// Hapus satu baris utuh — satu-satunya cara membatalkan baris berbobot.
+  const factory CheckoutFormEvent.removeLine(String lineId) = _RemoveLine;
+
+  const factory CheckoutFormEvent.updateLineNotes(
+    String lineId,
     String notes,
-  ) = _UpdateItemNotes;
+  ) = _UpdateLineNotes;
 
   const factory CheckoutFormEvent.updateOrderType(OrderType orderType) =
       _UpdateOrderType;
@@ -30,6 +47,6 @@ class CheckoutFormEvent with _$CheckoutFormEvent {
 
   const factory CheckoutFormEvent.orderAddedItems(Order? order) =
       _OrderAddedItems;
-    const factory CheckoutFormEvent.customerNameChanged(String name) =
+  const factory CheckoutFormEvent.customerNameChanged(String name) =
       _CustomerNameChanged;
 }