fix(billing): unify quota counters, fix Stripe webhooks, tier/plan sync

database/repositories.py

@@ -93,34 +93,45 @@ class UserRepository:
         self.db.commit()
         return True
 
-    def increment_usage(
-        self, user_id: str, docs: int = 0, pages: int = 0, api_calls: int = 0
-    ) -> Optional[User]:
-        """Increment usage counters"""
+    def reset_usage_if_needed(self, user_id: str) -> Optional[User]:
+        """Reset monthly counters if usage_reset_date is in a previous month."""
         user = self.get_by_id(user_id)
         if not user:
             return None
 
-        # Check if usage needs to be reset (monthly)
-        if user.usage_reset_date:
-            now = datetime.now(timezone.utc)
-            if (
-                now.month != user.usage_reset_date.month
-                or now.year != user.usage_reset_date.year
-            ):
-                user.docs_translated_this_month = 0
-                user.pages_translated_this_month = 0
-                user.api_calls_this_month = 0
-                user.usage_reset_date = now
-
-        user.docs_translated_this_month += docs
-        user.pages_translated_this_month += pages
-        user.api_calls_this_month += api_calls
-
-        self.db.commit()
-        self.db.refresh(user)
+        now = datetime.now(timezone.utc)
+        reset_date = user.usage_reset_date
+        if reset_date is None or reset_date.month != now.month or reset_date.year != now.year:
+            user.docs_translated_this_month = 0
+            user.pages_translated_this_month = 0
+            user.api_calls_this_month = 0
+            user.usage_reset_date = now
+            user.updated_at = now
+            self.db.commit()
+            self.db.refresh(user)
         return user
 
+    def increment_usage(
+        self, user_id: str, docs: int = 0, pages: int = 0, api_calls: int = 0
+    ) -> Optional[User]:
+        """Increment usage counters atomically via SQL UPDATE."""
+        from sqlalchemy import update
+
+        now = datetime.now(timezone.utc)
+        self.db.execute(
+            update(User)
+            .where(User.id == user_id)
+            .values(
+                docs_translated_this_month=User.docs_translated_this_month + docs,
+                pages_translated_this_month=User.pages_translated_this_month + pages,
+                api_calls_this_month=User.api_calls_this_month + api_calls,
+                updated_at=now,
+            )
+            .execution_options(synchronize_session=False)
+        )
+        self.db.commit()
+        return self.get_by_id(user_id)
+
     def add_credits(self, user_id: str, credits: int) -> Optional[User]:
         """Add extra credits to user"""
         user = self.get_by_id(user_id)
@@ -133,14 +144,21 @@ class UserRepository:
         return user
 
     def use_credits(self, user_id: str, credits: int) -> bool:
-        """Use credits from user balance"""
-        user = self.get_by_id(user_id)
-        if not user or user.extra_credits < credits:
-            return False
+        """Use credits from user balance atomically (prevents overdraft)."""
+        from sqlalchemy import update
 
-        user.extra_credits -= credits
+        now = datetime.now(timezone.utc)
+        result = self.db.execute(
+            update(User)
+            .where(User.id == user_id, User.extra_credits >= credits)
+            .values(
+                extra_credits=User.extra_credits - credits,
+                updated_at=now,
+            )
+            .execution_options(synchronize_session=False)
+        )
         self.db.commit()
-        return True
+        return result.rowcount > 0
 
     def get_all_users(
         self, skip: int = 0, limit: int = 100, plan: Optional[PlanType] = None