feat(discounts): добавлено комбинирование скидок по режимам

Добавлено поле combine_mode с тремя режимами:
- stack - складывать с другими скидками
- max_only - применять только максимальную
- exclusive - отменяет все остальные скидки

Изменения:
- Модель Discount: добавлено поле combine_mode
- Calculator: новый класс DiscountCombiner, методы возвращают списки скидок
- Applier: создание нескольких DiscountApplication записей
- Admin: отображение combine_mode с иконками
- POS API: возвращает списки применённых скидок
- POS UI: отображение нескольких скидок с иконками режимов

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

myproject/pos/views.py

@@ -1403,6 +1403,7 @@ def pos_checkout(request):
         "notes": str (optional),
         "promo_code": str (optional) - Промокод для скидки
         "manual_discount_id": int (optional) - ID выбранной вручную скидки
+        "custom_discount": dict (optional) - Произвольная скидка {"value": float, "is_percent": bool}
     }
     """
     from orders.models import Order, OrderItem, OrderStatus
@@ -1425,6 +1426,7 @@ def pos_checkout(request):
         order_notes = body.get('notes', '')
         promo_code = body.get('promo_code')  # Промокод для скидки
         manual_discount_id = body.get('manual_discount_id')  # ID выбранной вручную скидки
+        custom_discount = body.get('custom_discount')  # Произвольная скидка {"value": float, "is_percent": bool}
 
         if not customer_id:
             return JsonResponse({'success': False, 'error': 'Не указан клиент'}, status=400)
@@ -1556,7 +1558,38 @@ def pos_checkout(request):
             order.calculate_total()
 
             # 4. Применяем скидки
-            if manual_discount_id:
+            if custom_discount:
+                # Применяем произвольную скидку
+                from decimal import Decimal
+                discount_value = Decimal(str(custom_discount.get('value', 0)))
+                is_percent = custom_discount.get('is_percent', False)
+
+                if is_percent:
+                    # Процентная скидка
+                    discount_amount = order.subtotal * discount_value / 100
+                    discount_name = f'Произвольная скидка {discount_value}%'
+                else:
+                    # Фиксированная скидка
+                    discount_amount = min(discount_value, order.subtotal)
+                    discount_name = f'Произвольная скидка {discount_value} руб.'
+
+                order.discount_amount = discount_amount
+                order.applied_promo_code = discount_name  # Сохраняем название в поле промокода
+                order.save(update_fields=['discount_amount', 'applied_promo_code'])
+                order.calculate_total()
+
+                # Создаем запись о применении в истории скидок
+                from discounts.models import DiscountApplication
+                DiscountApplication.objects.create(
+                    order=order,
+                    target='order',
+                    base_amount=order.subtotal,
+                    discount_amount=discount_amount,
+                    final_amount=order.subtotal - discount_amount,
+                    customer=customer,
+                    applied_by=request.user
+                )
+            elif manual_discount_id:
                 from discounts.services.applier import DiscountApplier
                 from discounts.models import Discount
 
@@ -1762,22 +1795,40 @@ def validate_promo_code(request):
 def calculate_cart_discounts(request):
     """
     Рассчитать скидки для корзины POS.
+    Поддерживает комбинирование скидок по combine_mode.
 
     Payload JSON:
         {
             'items': [...],
             'promo_code': str (optional),
-            'customer_id': int (optional)
+            'customer_id': int (optional),
+            'manual_discount_id': int (optional),
+            'skip_auto_discount': bool (optional)
         }
 
     Returns JSON:
         {
             'success': true,
             'cart_subtotal': float,
-            'order_discount': {...},
-            'item_discounts': [...],
+            'order_discounts': [
+                {'discount_id': int, 'discount_name': str, 'discount_amount': float, 'combine_mode': str},
+                ...
+            ],
+            'total_order_discount': float,
+            'item_discounts': [
+                {
+                    'cart_index': int,
+                    'discounts': [
+                        {'discount_id': int, 'discount_name': str, 'discount_amount': float, 'combine_mode': str},
+                        ...
+                    ],
+                    'total_discount': float
+                },
+                ...
+            ],
             'total_discount': float,
-            'final_total': float
+            'final_total': float,
+            'excluded_by': {'id': int, 'name': str} или None
         }
     """
     from discounts.services.calculator import DiscountCalculator
@@ -1788,6 +1839,7 @@ def calculate_cart_discounts(request):
         items_data = data.get('items', [])
         promo_code = data.get('promo_code')
         customer_id = data.get('customer_id')
+        skip_auto_discount = data.get('skip_auto_discount', False)
 
         customer = None
         if customer_id:
@@ -1797,32 +1849,45 @@ def calculate_cart_discounts(request):
                 pass
 
         result = DiscountCalculator.calculate_cart_discounts(
-            items_data, promo_code, customer
+            items_data, promo_code, customer, skip_auto_discount=skip_auto_discount
         )
 
-        cart_subtotal = Decimal('0')
-        for item in items_data:
-            cart_subtotal += Decimal(str(item['price'])) * Decimal(str(item['quantity']))
+        # Форматируем item_discounts для JSON (Decimal -> float)
+        formatted_item_discounts = []
+        for item in result['item_discounts']:
+            formatted_discounts = []
+            for disc in item['discounts']:
+                formatted_discounts.append({
+                    'discount_id': disc['discount_id'],
+                    'discount_name': disc['discount_name'],
+                    'discount_amount': float(disc['discount_amount']),
+                    'combine_mode': disc['combine_mode']
+                })
+            formatted_item_discounts.append({
+                'cart_index': item['cart_index'],
+                'discounts': formatted_discounts,
+                'total_discount': float(item['total_discount'])
+            })
+
+        # Форматируем order_discounts для JSON
+        formatted_order_discounts = []
+        for disc in result['order_discounts']:
+            formatted_order_discounts.append({
+                'discount_id': disc['discount_id'],
+                'discount_name': disc['discount_name'],
+                'discount_amount': float(disc['discount_amount']),
+                'combine_mode': disc['combine_mode']
+            })
 
         response_data = {
             'success': True,
-            'cart_subtotal': float(cart_subtotal),
-            'order_discount': {
-                'discount_id': result['order_discount']['discount'].id if result['order_discount'].get('discount') else None,
-                'discount_name': result['order_discount']['discount'].name if result['order_discount'].get('discount') else None,
-                'discount_amount': float(result['order_discount']['discount_amount']),
-                'error': result['order_discount'].get('error'),
-            } if result['order_discount'] else None,
-            'item_discounts': [
-                {
-                    'cart_index': i['cart_index'],
-                    'discount_id': i['discount'].id,
-                    'discount_name': i['discount'].name,
-                    'discount_amount': float(i['discount_amount']),
-                } for i in result['item_discounts']
-            ],
+            'cart_subtotal': float(result['cart_subtotal']),
+            'order_discounts': formatted_order_discounts,
+            'total_order_discount': float(result['total_order_discount']),
+            'item_discounts': formatted_item_discounts,
             'total_discount': float(result['total_discount']),
             'final_total': float(result['final_total']),
+            'excluded_by': result.get('excluded_by')
         }
 
         return JsonResponse(response_data)
@@ -1881,7 +1946,8 @@ def get_available_discounts(request):
                 'name': d.name,
                 'discount_type': d.discount_type,
                 'value': float(d.value),
-                'min_order_amount': float(d.min_order_amount) if d.min_order_amount else None
+                'min_order_amount': float(d.min_order_amount) if d.min_order_amount else None,
+                'combine_mode': d.combine_mode
             })
 
         # Получаем автоматическую скидку (только одну для отображения)