update cart logic

backend/product/models.py

@@ -302,6 +302,18 @@ class ProductVariant(models.Model):
     def __str__(self):
         return f"{self.product.name} - {', '.join(str(attr) for attr in self.product_attributes.all())}"
         
+    @property
+    def price_before_discount(self):
+        return self.price
+
+    @property
+    def price_after_discount(self):
+        return self.price * (self.discount / 100)
+    
+    @property
+    def discount_amount(self):
+        return self.price * (self.discount / 100)
+    
     def set_or_update_price(self, dollor_price=None):
         if not dollor_price:
             dollor_object, _ = DollorModel.objects.get_or_create(unique_filed='unique')