refactor(business): Enhance promo validation and data representation

This commit improves the validation logic within the promo serializers and refines how promotion data is handled and displayed.

Key changes:
- **Improved Validation:** The validation logic now correctly handles partial updates (`PATCH`) by checking the `mode` from the instance if it's not provided in the request data. It also prevents `max_count` from being set lower than the current `used_count` for a promo.
- **Accurate Used Count:** The `get_used_codes_count` method on the `Promo` model now correctly returns the `used_count` for promotions in `COMMON` mode.

Author: RandomProgramm3r

promo_code/business/models.py

@@ -119,8 +119,7 @@ def get_comment_count(self) -> int:
     def get_used_codes_count(self) -> int:
         if self.mode == business.constants.PROMO_MODE_UNIQUE:
             return self.unique_codes.filter(is_used=True).count()
-        # TODO: COMMON Promo
-        return 0
+        return self.used_count
 
     @property
     def get_available_unique_codes(self) -> list[str] | None:

promo_code/business/serializers.py

@@ -285,81 +285,67 @@ class Meta:
         )
 
     def validate(self, data):
-        full_data = self._get_full_data(data)
+        """
+        Main validation method.
+        Determines the mode and calls the corresponding validation method.
+        """
 
-        mode = full_data.get('mode')
+        mode = data.get('mode', getattr(self.instance, 'mode', None))
 
         if mode == business.constants.PROMO_MODE_COMMON:
-            self._validate_common(full_data)
-
+            self._validate_common(data)
         elif mode == business.constants.PROMO_MODE_UNIQUE:
-            self._validate_unique(full_data)
-
+            self._validate_unique(data)
+        elif mode is None:
+            raise rest_framework.serializers.ValidationError(
+                {'mode': 'This field is required.'},
+            )
         else:
             raise rest_framework.serializers.ValidationError(
                 {'mode': 'Invalid mode.'},
             )
 
         return data
 
-    def to_representation(self, instance):
-        """
-        Controls the display of fields in the response.
-        """
-        data = super().to_representation(instance)
-
-        if not instance.image_url:
-            data.pop('image_url', None)
-
-        if instance.mode == business.constants.PROMO_MODE_UNIQUE:
-            data.pop('promo_common', None)
-            if 'promo_unique' in self.fields and isinstance(
-                self.fields['promo_unique'],
-                rest_framework.serializers.SerializerMethodField,
-            ):
-                data['promo_unique'] = self.get_promo_unique(instance)
-            else:
-                data['promo_unique'] = [
-                    code.code for code in instance.unique_codes.all()
-                ]
-        else:
-            data.pop('promo_unique', None)
-
-        return data
-
-    def _get_full_data(self, data):
-        """
-        Build the full data dict by merging existing instance data
-        with new input.
-        """
-        if self.instance:
-            full_data = self.to_representation(self.instance)
-            full_data.update(data)
-        else:
-            full_data = data
-        return full_data
-
-    def _validate_common(self, full_data):
+    def _validate_common(self, data):
         """
         Validations for COMMON promo mode.
         """
-        promo_common = full_data.get('promo_common')
-        promo_unique = full_data.get('promo_unique')
-        max_count = full_data.get('max_count')
 
-        if not promo_common:
+        if 'promo_unique' in data and data['promo_unique'] is not None:
             raise rest_framework.serializers.ValidationError(
-                {'promo_common': 'This field is required for COMMON mode.'},
+                {'promo_unique': 'This field is not allowed for COMMON mode.'},
             )
 
-        if promo_unique is not None:
+        if self.instance is None and not data.get('promo_common'):
             raise rest_framework.serializers.ValidationError(
-                {'promo_unique': 'This field is not allowed for COMMON mode.'},
+                {'promo_common': 'This field is required for COMMON mode.'},
             )
 
+        new_max_count = data.get('max_count')
+        if self.instance and new_max_count is not None:
+            used_count = self.instance.get_used_codes_count
+            if used_count > new_max_count:
+                raise rest_framework.serializers.ValidationError(
+                    {
+                        'max_count': (
+                            f'max_count ({new_max_count}) cannot be less than '
+                            f'used_count ({used_count}).'
+                        ),
+                    },
+                )
+
+        effective_max_count = (
+            new_max_count
+            if new_max_count is not None
+            else getattr(self.instance, 'max_count', None)
+        )
+
         min_c = business.constants.PROMO_COMMON_MIN_COUNT
         max_c = business.constants.PROMO_COMMON_MAX_COUNT
-        if not (min_c <= max_count <= max_c):
+        if effective_max_count is not None and not (
+            min_c <= effective_max_count <= max_c
+        ):
             raise rest_framework.serializers.ValidationError(
                 {
                     'max_count': (
@@ -368,35 +354,67 @@ def _validate_common(self, full_data):
                 },
             )
 
-    def _validate_unique(self, full_data):
+    def _validate_unique(self, data):
         """
         Validations for UNIQUE promo mode.
         """
-        promo_common = full_data.get('promo_common')
-        promo_unique = full_data.get('promo_unique')
-        max_count = full_data.get('max_count')
 
-        if not promo_unique:
+        if 'promo_common' in data and data['promo_common'] is not None:
             raise rest_framework.serializers.ValidationError(
-                {'promo_unique': 'This field is required for UNIQUE mode.'},
+                {'promo_common': 'This field is not allowed for UNIQUE mode.'},
             )
 
-        if promo_common is not None:
+        if self.instance is None and not data.get('promo_unique'):
             raise rest_framework.serializers.ValidationError(
-                {'promo_common': 'This field is not allowed for UNIQUE mode.'},
+                {'promo_unique': 'This field is required for UNIQUE mode.'},
             )
 
-        if max_count != business.constants.PROMO_UNIQUE_MAX_COUNT:
+        effective_max_count = data.get(
+            'max_count',
+            getattr(self.instance, 'max_count', None),
+        )
+
+        if (
+            effective_max_count is not None
+            and effective_max_count
+            != business.constants.PROMO_UNIQUE_MAX_COUNT
+        ):
             raise rest_framework.serializers.ValidationError(
                 {
                     'max_count': (
                         'Must be equal to '
-                        f'{business.constants.PROMO_UNIQUE_MAX_COUNT}'
+                        f'{business.constants.PROMO_UNIQUE_MAX_COUNT} '
                         'for UNIQUE mode.'
                     ),
                 },
             )
 
+    def to_representation(self, instance):
+        """
+        Controls the display of fields in the response.
+        """
+
+        data = super().to_representation(instance)
+
+        if not instance.image_url:
+            data.pop('image_url', None)
+
+        if instance.mode == business.constants.PROMO_MODE_UNIQUE:
+            data.pop('promo_common', None)
+            if 'promo_unique' in self.fields and isinstance(
+                self.fields['promo_unique'],
+                rest_framework.serializers.SerializerMethodField,
+            ):
+                data['promo_unique'] = self.get_promo_unique(instance)
+            else:
+                data['promo_unique'] = [
+                    code.code for code in instance.unique_codes.all()
+                ]
+        else:
+            data.pop('promo_unique', None)
+
+        return data
+
 
 class PromoCreateSerializer(BasePromoSerializer):
     url = rest_framework.serializers.HyperlinkedIdentityField(