fix order model invoice genrator

backend/order/models.py

@@ -250,7 +250,25 @@ class OrderItemModel(models.Model):
 
     def __str__(self):
         return f'({self.product}) - ({self.order.user})'
-
+    
+    # @property
+    def total_price_before_discount(self):
+        return self.price * self.quantity
+    
+    # @property
+    def total_product_discount_amount(self):
+        if self.discount_percent > 0:
+            return int((self.price * self.quantity) * (self.discount_percent / 100))
+        return 0
+    
+    # @property
+    def price_after_special_discount(self):
+        all_discounts = (self.special_discount_amount or 0) + self.total_product_discount_amount()
+        print(all_discounts)
+        return self.total_price_before_discount() - all_discounts
+    
+    def unit_price(self):
+        return self.price
 
 class ShopOrderModel(models.Model):
     """Represents the portion of a customer Order that belongs to a single Shop.