feat(pos): интеграция системы скидок в POS терминал

API endpoints:
- POST /api/discounts/validate-promo/: валидация промокода
- POST /api/discounts/calculate/: расчёт скидок для корзины

Обновлён pos_checkout:
- добавлен параметр promo_code в payload
- автоматическое применение скидок к заказу

UI (terminal.html):
- секция скидок в модальном окне оплаты
- поле ввода промокода
- отображение автоматических скидок
- кнопки применения/удаления промокода

JavaScript (terminal.js):
- переменные состояния скидок
- функции applyPromoCode, removePromoCode
- checkAutoDiscounts: проверка автоматических скидок
- updateCheckoutTotalWithDiscounts: пересчёт итога
- обработчики кнопок промокода

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

myproject/pos/views.py

@@ -1400,7 +1400,8 @@ def pos_checkout(request):
             {"payment_method": "cash"|"card"|"online"|"account_balance", "amount": float, "notes": str},
             ...
         ],
-        "notes": str (optional)
+        "notes": str (optional),
+        "promo_code": str (optional) - Промокод для скидки
     }
     """
     from orders.models import Order, OrderItem, OrderStatus
@@ -1421,6 +1422,7 @@ def pos_checkout(request):
         items_data = body.get('items', [])
         payments_data = body.get('payments', [])
         order_notes = body.get('notes', '')
+        promo_code = body.get('promo_code')  # Промокод для скидки
 
         if not customer_id:
             return JsonResponse({'success': False, 'error': 'Не указан клиент'}, status=400)
@@ -1551,7 +1553,22 @@ def pos_checkout(request):
             order.refresh_from_db()
             order.calculate_total()
 
-            # 4. Проводим платежи
+            # 4. Применяем скидки
+            if promo_code:
+                from discounts.services.applier import DiscountApplier
+                apply_result = DiscountApplier.apply_promo_code(
+                    order=order,
+                    promo_code=promo_code,
+                    user=request.user
+                )
+                if not apply_result['success']:
+                    raise ValidationError(apply_result['error'])
+            else:
+                # Применяем автоматические скидки
+                from discounts.services.applier import DiscountApplier
+                DiscountApplier.apply_auto_discounts(order, user=request.user)
+
+            # 5. Проводим платежи
             payments_list = []
             for payment_data in payments_data:
                 payments_list.append({
@@ -1652,3 +1669,149 @@ def create_order_draft(request):
     except Exception as e:
         logger.error(f'Ошибка при создании черновика заказа: {str(e)}', exc_info=True)
         return JsonResponse({'success': False, 'error': f'Ошибка: {str(e)}'}, status=500)
+
+
+# ============================================
+# DISCOUNT API
+# ============================================
+
+@login_required
+@require_http_methods(["POST"])
+def validate_promo_code(request):
+    """
+    Валидировать промокод.
+
+    Payload JSON:
+        {
+            'promo_code': str,
+            'cart_total': decimal (optional)
+        }
+
+    Returns JSON:
+        {
+            'success': true/false,
+            'promo_code': {...},
+            'error': str
+        }
+    """
+    from discounts.services.validator import DiscountValidator
+    from customers.models import Customer
+
+    try:
+        data = json.loads(request.body)
+        promo_code = data.get('promo_code', '')
+        cart_total = data.get('cart_total', '0')
+
+        # Получаем текущего клиента из Redis
+        from django.core.cache import cache
+        cart_key = f'pos:customer:{request.user.id}'
+        customer_id = cache.get(cart_key)
+
+        customer = None
+        if customer_id:
+            try:
+                customer = Customer.objects.get(id=customer_id)
+            except Customer.DoesNotExist:
+                pass
+
+        is_valid, promo, error = DiscountValidator.validate_promo_code(
+            promo_code, customer, Decimal(str(cart_total)) if cart_total else None
+        )
+
+        if is_valid:
+            return JsonResponse({
+                'success': True,
+                'promo_code': {
+                    'code': promo.code,
+                    'discount_id': promo.discount.id,
+                    'discount_name': promo.discount.name,
+                    'discount_type': promo.discount.discount_type,
+                    'discount_value': float(promo.discount.value),
+                    'scope': promo.discount.scope,
+                }
+            })
+        else:
+            return JsonResponse({'success': False, 'error': error})
+
+    except json.JSONDecodeError:
+        return JsonResponse({'success': False, 'error': 'Неверный формат JSON'}, status=400)
+    except Exception as e:
+        logger.error(f'Ошибка при валидации промокода: {str(e)}', exc_info=True)
+        return JsonResponse({'success': False, 'error': f'Ошибка: {str(e)}'}, status=500)
+
+
+@login_required
+@require_http_methods(["POST"])
+def calculate_cart_discounts(request):
+    """
+    Рассчитать скидки для корзины POS.
+
+    Payload JSON:
+        {
+            'items': [...],
+            'promo_code': str (optional),
+            'customer_id': int (optional)
+        }
+
+    Returns JSON:
+        {
+            'success': true,
+            'cart_subtotal': float,
+            'order_discount': {...},
+            'item_discounts': [...],
+            'total_discount': float,
+            'final_total': float
+        }
+    """
+    from discounts.services.calculator import DiscountCalculator
+    from customers.models import Customer
+
+    try:
+        data = json.loads(request.body)
+        items_data = data.get('items', [])
+        promo_code = data.get('promo_code')
+        customer_id = data.get('customer_id')
+
+        customer = None
+        if customer_id:
+            try:
+                customer = Customer.objects.get(id=customer_id)
+            except Customer.DoesNotExist:
+                pass
+
+        result = DiscountCalculator.calculate_cart_discounts(
+            items_data, promo_code, customer
+        )
+
+        cart_subtotal = Decimal('0')
+        for item in items_data:
+            cart_subtotal += Decimal(str(item['price'])) * Decimal(str(item['quantity']))
+
+        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']
+            ],
+            'total_discount': float(result['total_discount']),
+            'final_total': float(result['final_total']),
+        }
+
+        return JsonResponse(response_data)
+
+    except json.JSONDecodeError:
+        return JsonResponse({'success': False, 'error': 'Неверный формат JSON'}, status=400)
+    except Exception as e:
+        logger.error(f'Ошибка при расчете скидок: {str(e)}', exc_info=True)
+        return JsonResponse({'success': False, 'error': f'Ошибка: {str(e)}'}, status=500)