💰 Backend Ledger

A scalable backend system for handling financial transactions, ledger entries, and account management with JWT-based authentication and MongoDB transactional integrity.

The system uses MongoDB transactions to maintain financial consistency and a TTL-based blacklist collection for automatically expiring revoked JWT tokens

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🚀 Tech Stack

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📁 Project Structure

Backend_Ledger/
│
├── server.js                        ← Entry point
├── package.json
├── .env                             ← Environment variables (not committed)
│
└── src/
    ├── app.js                       ← Express app setup, route mounting
    │
    ├── config/
    │   └── db.js                    ← MongoDB connection
    │
    ├── controllers/
    │   ├── auth.controller.js
    │   ├── account.controller.js
    │   └── transaction.controller.js
    │
    ├── middleware/
    │   └── auth.middleware.js       ← JWT verification (user + system)
    │
    ├── models/
    │   ├── user.model.js
    │   ├── account.model.js
    │   ├── transaction.model.js
    │   └── ledger.model.js
        └── blacklist.model.js ← Revoked JWTs with TTL expiration
    │
    ├── routes/
    │   ├── auth.routes.js
    │   ├── account.routes.js
    │   └── transaction.routes.js
    │
    └── services/
        └── email.service.js         ← Nodemailer email service

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📌 API Endpoints

🔐 Auth — /api/auth

Method	Endpoint	Access	Description
POST	/api/auth/register	Public	Register a new user
POST	/api/auth/login	Public	Login and receive JWT cookie

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🏦 Accounts — /api/accounts

Method	Endpoint	Access	Description
POST	/api/accounts/	🔒 Protected	Create a new account
GET	/api/accounts/all-accounts	🔒 Protected	Get all accounts for logged-in user
GET	/api/accounts/balance/:accountId	🔒 Protected	Get balance of a specific account

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💸 Transactions — /api/transactions

Method	Endpoint	Access	Description
POST	/api/transactions/	🔒 Protected	Create a new transaction
POST	/api/transactions/system/inital-funds	🔒 System Only	Seed initial funds (system middleware)

🔒 Protected = requires valid JWT token in cookie
🔒 System Only = requires system-level JWT (authSystemUserMiddleware)

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🔑 Authentication Flow

Client Request
      │
      ▼
authMiddleware (auth.middleware.js)
      │
      ├── Reads JWT from cookie
      ├── Verifies token
      └── Attaches user to req → Controller

Two middleware levels:

• authMiddleware — for regular authenticated users
• authSystemUserMiddleware — for internal system operations (e.g. seeding funds)

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⚙️ Setup & Installation

1. Clone the repo

git clone https://github.com/amitava-code/Backend_Ledger.git
cd Backend_Ledger

2. Install dependencies

npm install

3. Create .env file

PORT=3000
MONGO_URI=mongodb://localhost:27017/ledger_db
JWT_SECRET=your_jwt_secret_here
JWT_SYSTEM_SECRET=your_system_jwt_secret_here
EMAIL_USER=your_email@gmail.com
EMAIL_PASS=your_email_password

4. Run the server

# Development (with nodemon)
npm run dev

# Production
npm start

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🧪 Test the API

# Register
curl -X POST http://localhost:3000/api/auth/register \
  -H "Content-Type: application/json" \
  -d '{"name":"John","email":"john@example.com","password":"123456"}'

# Login
curl -X POST http://localhost:3000/api/auth/login \
  -H "Content-Type: application/json" \
  -d '{"email":"john@example.com","password":"123456"}'

# Create Account (with cookie from login)
curl -X POST http://localhost:3000/api/accounts/ \
  -H "Content-Type: application/json" \
  --cookie "token=<your_jwt_here>"

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📊 Data Models

Model	Description
user.model.js	User credentials and profile
account.model.js	Financial account per user
transaction.model.js	Debit/credit transaction records
ledger.model.js	Double-entry ledger entries

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👨‍💻 Author

Amitava Biswas — Backend Developer

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🤝 Contributing

This is a personal learning project. Contributions and suggestions are welcome — feel free to open an issue or PR.