Notification System

A multi-channel notification delivery system with subscription management and real-time notification tracking.

Overview

The Notification System is a low-level design implementation of a notification platform. It manages user subscriptions to channels, delivers notifications through multiple channels, tracks delivery status, and provides notification history.

Features

Core Functionality

• Add Users: Register users in the system
• Subscribe: Subscribe users to notification channels
• Send Notifications: Deliver to all channel subscribers
• Mark as Read: Track read status
• Get Notifications: View user notifications
• Unread Count: Get unread notification count
• History: View full notification history

Notification Channels

• EMAIL: Email delivery
• SMS: Text message delivery
• PUSH: Push notifications
• IN_APP: In-application notifications

Priority Levels

• LOW: Non-urgent information
• MEDIUM: Standard priority
• HIGH: Important notifications
• CRITICAL: Emergency alerts

Architecture

Design Patterns

• Singleton Pattern: Single NotificationService instance
• Observer Pattern: Subscription and notification publishing
• Strategy Pattern: Different notification channels

Components

Models

• Notification: Individual notification record
• NotificationType: Enumeration (EMAIL, SMS, PUSH, IN_APP)
• Priority: Enumeration (LOW, MEDIUM, HIGH, CRITICAL)

Services

• NotificationService:
  • Manages users
  • Handles subscriptions
  • Sends notifications
  • Tracks read status
  • Generates reports

Usage

python main.py

Example Workflow

notificationService = NotificationService.getInstance()

# Create users
user_id = notificationService.addUser("Alice")

# Subscribe to channel
notificationService.subscribe(user_id, "news")

# Send notification
notificationService.sendNotification(
    channel="news",
    message="Breaking news alert",
    notification_type=NotificationType.EMAIL,
    priority=Priority.HIGH
)

# Get notifications
notificationService.getUserNotifications(user_id)

# Mark as read
notificationService.markAsRead(user_id, notification_id)

# Get unread count
count = notificationService.getUnreadCount(user_id)

# View history
notificationService.getNotificationHistory(user_id)

Key Implementation Details

• Channel Broadcasting: Notifications sent to all channel subscribers
• Read Status: Tracks per-notification read status
• Subscription Management: Users can subscribe/unsubscribe
• Multi-channel: Same notification sent via different channels
• Priority Routing: High-priority notifications flagged
• Delivery Simulation: Prints delivery method
• History Preservation: All notifications retained
• Unread Tracking: Efficient unread counting

Constraints & Assumptions

• User IDs auto-generated
• Notification IDs auto-generated
• Channels created on first subscription
• Channels destroyed when no subscribers
• User can subscribe multiple times (idempotent)
• Unsubscribe requires active subscription
• Notifications never deleted
• No notification expiration
• In-memory only (no persistence)

Possible Enhancements

• Persistent storage
• Notification scheduling
• Delayed delivery
• Retry logic for failed deliveries
• Rate limiting per channel
• Notification templates
• Dynamic channel creation
• User notification preferences
• Frequency capping
• Do-not-disturb hours
• Rich media support
• Clickable actions in notifications
• Notification groups
• Read receipts
• Delivery status tracking
• A/B testing
• Analytics and reporting
• Webhook integrations
• Third-party providers (Twilio, SendGrid)

Notification Channels

Type	Method	Use Case
EMAIL	Email	Long-form notifications
SMS	Text Message	Urgent alerts
PUSH	App Push	Mobile notifications
IN_APP	In-application	User interface alerts

Priority Levels

Level	Use Case	Response Time
LOW	Newsletter	Non-urgent
MEDIUM	Standard	Normal processing
HIGH	Important	Fast
CRITICAL	Emergency	Immediate

Time Complexity

• Add User: O(1)
• Subscribe: O(1)
• Send Notification: O(s) where s = subscribers
• Mark as Read: O(1)
• Get Unread Count: O(n) where n = notifications
• Get Notifications: O(n)
• Get History: O(n)

Space Complexity

• O(u + c + n) where u = users, c = channels, n = notifications