📬 Notification System

A modular, scalable, and extensible notification system built with NestJS, BullMQ, and TypeORM, designed to handle queued and immediate notification delivery through various strategies (email, SMS, etc.).

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🧠 Assumptions

• Each notification type has its own strategy implementing a common NotificationStrategy interface.
• Currently only email is implemented; others can be easily extended.
• Redis is used for BullMQ queue handling.
• Notifications and delivery attempts are saved in a PostgreSQL database.
• Clean Architecture principles are used for separation of concerns.

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🛠️ Setup Instructions

1. Clone the repo

  git clone https://github.com/amir-mirjalili/notification-system.git
  cd notification-system

2. Install dependencies

  npm install

3. Configure environment variables

Create a .env file:

DB_HOST=localhost
DB_PORT=5432
DB_USER=USER
DB_PASS=PASSWORD
DB_NAME=DBNAME

4. Run database migrations

  npm run migration:create

5. Start the application

  npm run start:dev

6. test the application

  npm run test

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🧱 Architecture Overview

src/
    :moduleName
        ├── entities/              # TypeORM Entities (Notification, Attempt)
        ├── strategies/            # Notification strategies (EmailStrategy)
        ├── queue/                 # Queue processor logic (BullMQ)
        ├── notification/          # Core module and service
        ├── exceptions/            # Custom exceptions like RetryableException
        └── main.ts                # App bootstrap

🔁 Features:

• BullMQ Queue: Background job processing.
• Persistence: All attempts tracked with success/failure.
• Pluggable Strategies: Easy to add new channels (SMS, Push).

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🧪 Sample API Usage

Queue a Notification:

await notificationService.send('EMAIL', {
  recipient: 'user@example.com',
  subject: 'Welcome!',
  data: {
    template: 'welcome',
    templateData: { name: 'Amir' },
  },
});

Send Immediately:

await notificationService.sendImmediate('EMAIL', {
  recipient: 'user@example.com',
  subject: 'Your OTP',
  data: {
    template: 'otp',
    templateData: { code: '123456' },
  },
});

📈 Future Enhancements

• Add SMS/Push strategies
• Notification templates (Handlebars or EJS)
• Multi-tenant support
• Dashboard for retry/resend & analytics

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🧑‍💻 Author

Amir Mirjalili
GitHub: amir-mirjalili

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📄 License

MIT License