feat: add validation to prevent multiple free plan purchases within a month

- Add FREE_PLAN_LIMIT_EXCEEDED error message in Persian
- Implement validation logic in subscribeToPlan method to check for existing free plan subscriptions
- Users can only purchase free plans once per month
- Added MoreThan import from TypeORM for date comparison

src/common/enums/message.enum.ts

@@ -488,6 +488,7 @@ export const enum SubscriptionMessage {
   SLUG_STRING = "اسلاگ باید یک رشته باشد",
   SLUG_LENGTH = "اسلاگ باید بین ۴ تا ۲۵۰ کاراکتر باشد",
   SLUG_EXISTS = "این اسلاگ قبلا ثبت شده است",
+  FREE_PLAN_LIMIT_EXCEEDED = "شما در یک ماه گذشته از پلن رایگان استفاده کرده‌اید و نمی‌توانید مجدداً استفاده کنید",
   USER_DOES_NOT_HAVE_ACCESS = "شما دسترسی به این سرویس ندارید",
 }
 

src/modules/subscriptions/providers/subscriptions.service.ts

@@ -4,7 +4,7 @@ import { Queue } from "bullmq";
 import dayjs from "dayjs";
 import Decimal from "decimal.js";
 import slugify from "slugify";
-import { DataSource, In, Not, QueryRunner } from "typeorm";
+import { DataSource, In, MoreThan, Not, QueryRunner } from "typeorm";
 
 import { ServiceMessage, SubscriptionMessage } from "../../../common/enums/message.enum";
 import { DanakServicesService } from "../../danak-services/providers/danak-services.service";
@@ -225,6 +225,24 @@ export class SubscriptionsService {
       });
       if (!plan) throw new BadRequestException(SubscriptionMessage.NOT_FOUND);
 
+      if (plan.isFree) {
+        const oneMonthAgo = dayjs().subtract(1, "month").toDate();
+        const existingFreePlanSubscription = await queryRunner.manager.findOne(UserSubscription, {
+          where: {
+            user: { id: userId },
+            plan: { isFree: true },
+            startDate: MoreThan(oneMonthAgo),
+          },
+          relations: {
+            plan: true,
+          },
+        });
+
+        if (existingFreePlanSubscription) {
+          throw new BadRequestException(SubscriptionMessage.FREE_PLAN_LIMIT_EXCEEDED);
+        }
+      }
+
       const startDate = dayjs().toDate();
       const endDate = dayjs().add(plan.duration, "day").toDate();