Case Study: Notification System

Example

**Example notification flow:** ```typescript // Order shipped → multiple channels await notificationApi.send({ eventType: 'order.shipped', userId: 'user123', data: { orderId: 'ORD-456', trackingNumber: '1Z999AA10123456784', carrier: 'UPS', estimatedDelivery: '2024-01-20' } }); // Results in: // 1. Push: "Your order is on its way! Track: 1Z999..." // 2. Email: Full HTML email with tracking link // 3. In-app: Notification in inbox ```

What did you learn about Notification System architecture?

Example

**Rich notification on iOS:** ```typescript // Notification with image and actions await pushService.send(userId, { title: 'New message from John', body: 'Hey, are you coming to the party?', imageUrl: 'https://cdn.app.com/avatars/john.jpg', categoryId: 'MESSAGE', // Enables action buttons data: { type: 'message', senderId: 'john123', threadId: 'thread456' } }); // iOS notification extension renders: // ┌──────────────────────────────┐ // │ [John's avatar] │ // │ New message from John │ // │ Hey, are you coming to... │ // │ ───────────────────────── │ // │ [Reply] [Mark Read] [Mute] │ // └──────────────────────────────┘ ```

What did you learn about push notifications: FCM and APNs?

Example

**Notification batching:** ```typescript // Instead of sending 20 "X liked your post" notifications: class NotificationBatcher { async batchSimilarNotifications( userId: string, eventType: string ): Promise<BatchedNotification | null> { const key = `pending:${userId}:${eventType}`; const pending = await this.redis.lrange(key, 0, -1); if (pending.length < 5) { return null; // Not enough to batch } // Clear pending await this.redis.del(key); const events = pending.map(JSON.parse); if (eventType === 'new_like') { return { title: `${events[0].userName} and ${events.length - 1} others liked your post`, body: null, data: { type: 'batched_likes', postId: events[0].postId, count: events.length } }; } // Similar for new_follower, new_comment, etc. } } ```

What did you learn about user preferences and rate limiting?

Example

**Channel-specific templates:** ```typescript // Same event, different templates per channel // Push (short, actionable) const pushTemplate = { title: '🎉 Flash Sale!', body: '50% off everything. Ends in {{hoursLeft}}h' }; // Email (detailed) const emailTemplate = { subject: 'Don\'t miss out! 50% Flash Sale', htmlBody: ` <h1>Flash Sale is ON!</h1> <p>Hi {{userName}},</p> <p>For the next {{hoursLeft}} hours, enjoy 50% off on all items.</p> <a href="{{shopUrl}}" class="cta">Shop Now</a> ` }; // SMS (ultra-short) const smsTemplate = { body: 'Flash Sale! 50% off for {{hoursLeft}}h. Shop: {{shortLink}}' }; ```

What did you learn about template engine and localization?

Example

**Real-time delivery monitoring:** ```typescript // Dashboard websocket for ops team class DeliveryMonitor { async getRealTimeStats(): Promise<RealTimeStats> { const now = new Date(); const fiveMinAgo = new Date(now.getTime() - 5 * 60 * 1000); return { sent: await this.redis.zcount('sent', fiveMinAgo, now), delivered: await this.redis.zcount('delivered', fiveMinAgo, now), failed: await this.redis.zcount('failed', fiveMinAgo, now), // Alert thresholds deliveryRate: 0.982, // Should be > 0.95 avgLatencyMs: 1250, // Should be < 5000 // Provider status providers: { fcm: { status: 'healthy', latency: 450 }, apns: { status: 'healthy', latency: 380 }, sendgrid: { status: 'degraded', latency: 2100 } } }; } } ```

What did you learn about delivery tracking and analytics?