FRE-4521 Implement Redis integration for rate limiting and deduplication

- Add ioredis dependency for Redis connection pooling
- Create RedisService singleton with connection management
- Add Redis config (url, dedupWindowSeconds) to notification.config.ts
- Implement NotificationService.checkRateLimit using Redis INCR+EXPIRE
- Implement NotificationService.deduplicateNotification using Redis SET/NX
- Add configurable rate limit windows and thresholds via env vars
- Add 29 unit tests covering Redis operations, rate limiting, and dedup
- All tests pass, TypeScript compiles cleanly for new files

packages/shared-notifications/src/services/notification.service.ts

@@ -2,6 +2,8 @@ import { EmailService } from './email.service';
 import { SMSService } from './sms.service';
 import { PushService } from './push.service';
 import { TemplateService } from './template.service';
+import { RedisService } from './redis.service';
+import { loadNotificationConfig } from '../config/notification.config';
 import type {
   Notification,
   NotificationChannel,
@@ -11,11 +13,21 @@ import type {
 } from '../types/notification.types';
 import type { TemplateResolutionOptions } from '../types/template.types';
 
+export interface RateLimitResult {
+  allowed: boolean;
+  currentCount: number;
+  limit: number;
+  remaining: number;
+  resetInSeconds: number;
+}
+
 export class NotificationService {
   private static instance: NotificationService;
   private emailService: EmailService;
   private smsService: SMSService;
   private pushService: PushService;
+  private redisService: RedisService;
+  private config: ReturnType<typeof loadNotificationConfig>;
   private pendingDeduplication = new Map<string, Set<string>>();
   private preferenceCache = new Map<string, NotificationPreference>();
 
@@ -23,6 +35,8 @@ export class NotificationService {
     this.emailService = EmailService.getInstance();
     this.smsService = SMSService.getInstance();
     this.pushService = PushService.getInstance();
+    this.config = loadNotificationConfig();
+    this.redisService = RedisService.getInstance({ url: this.config.redis.url });
   }
 
   static getInstance(): NotificationService {
@@ -204,7 +218,65 @@ export class NotificationService {
     }
   }
 
+  async checkRateLimit(
+    identifier: string,
+    channel: NotificationChannel,
+    customLimit?: number,
+    customWindowSeconds?: number
+  ): Promise<RateLimitResult> {
+    const limit = customLimit || this.getLimitForChannel(channel);
+    const windowSeconds = customWindowSeconds || this.config.rateLimits.windowSeconds;
+    const key = `rl:${channel}:${identifier}`;
+
+    const currentCount = await this.redisService.increment(key, windowSeconds);
+    const ttl = await this.redisService.getTTL(key);
+
+    return {
+      allowed: currentCount <= limit,
+      currentCount,
+      limit,
+      remaining: Math.max(0, limit - currentCount),
+      resetInSeconds: Math.max(1, ttl),
+    };
+  }
+
+  async deduplicateNotification(
+    dedupKey: DeduplicationKey,
+    customWindowSeconds?: number
+  ): Promise<boolean> {
+    const dedupId = `dedup:${dedupKey.userId}:${dedupKey.templateId}:${dedupKey.key}`;
+    const windowSeconds = customWindowSeconds || dedupKey.windowSeconds || this.config.redis.dedupWindowSeconds;
+
+    const wasSet = await this.redisService.setIfNotExists(dedupId, '1', windowSeconds);
+    return wasSet;
+  }
+
+  getRateLimitConfig(): {
+    emailPerMinute: number;
+    smsPerMinute: number;
+    pushPerMinute: number;
+    windowSeconds: number;
+  } {
+    return {
+      emailPerMinute: this.config.rateLimits.emailPerMinute,
+      smsPerMinute: this.config.rateLimits.smsPerMinute,
+      pushPerMinute: this.config.rateLimits.pushPerMinute,
+      windowSeconds: this.config.rateLimits.windowSeconds,
+    };
+  }
+
   getTemplateService(): TemplateService {
     return TemplateService.getInstance();
   }
+
+  private getLimitForChannel(channel: NotificationChannel): number {
+    switch (channel) {
+      case 'email':
+        return this.config.rateLimits.emailPerMinute;
+      case 'sms':
+        return this.config.rateLimits.smsPerMinute;
+      case 'push':
+        return this.config.rateLimits.pushPerMinute;
+    }
+  }
 }