BankTransactions Backend

A robust backend application for a banking system, built with Node.js, Express, and MongoDB. This system handles secure user authentication, account creation, and money transfers with transactional integrity.

🚀 Features

• User Authentication: Secure Register and Login with JWT and Cookies.
• Account Management: valid user can create an account and check balance.
• Secure Transactions: Money transfers between accounts using MongoDB Transactions (ACID properties) to ensure data consistency.
• Idempotency: Prevents duplicate transactions using idempotencyKey.
• Email Notifications: Integration with Gmail to send alerts for registration and transactions.
• System Funds: endpoint to inject initial funds into accounts.

🛠️ Tech Stack

• Runtime: Node.js
• Framework: Express.js
• Database: MongoDB (Mongoose)
• Authentication: JSON Web Tokens (JWT)

🏗️ Architecture & Flows

Transaction Flow

The system ensures that money is safely transferred by using a database session. If any step fails (e.g., insufficient funds, database error), the entire operation is rolled back.

sequenceDiagram
    participant User
    participant API
    participant DB as MongoDB
    participant Email as Email Service

    User->>API: POST /api/transactions
    API->>DB: Check Sender Balance & Account Status
    alt Insufficient Balance / Invalid
        API-->>User: Error (400/404)
    else Valid verification
        API->>DB: Start Session & Transaction
        API->>DB: Create Ledger (Debit Sender)
        API->>DB: Create Ledger (Credit Receiver)
        API->>DB: Update Transaction Status -> Completed
        API->>DB: Commit Transaction
        API->>Email: Send Transaction Alert
        API-->>User: Success (200)
    end

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🔌 API Endpoints

1. Authentication

Base URL: /api/auth

Method	Endpoint	Description	Body Parameters
POST	/register	Register a new user	name, email, password
POST	/login	Login user & get cookie	email, password

2. Accounts

Base URL: /api/accounts (Protected Routes)

Method	Endpoint	Description	Body Parameters
POST	/	Create a new bank account	None (Uses logged-in user)
GET	/	Get my account details	None
GET	/balance/:accountid	Get balance by Account ID	None

3. Transactions

Base URL: /api/transactions (Protected Routes)

Method	Endpoint	Description	Body Parameters
POST	/	Transfer money between accounts	fromAccount, toAccount, amount, idempotencyKey
POST	/system/initial-funds	Inject initial funds (System)	toAccount (or userId), amount, idempotencyKey

📦 Request Body Examples

Register User

{
  "name": "Jane Doe",
  "email": "jane@example.com",
  "password": "securepassword123"
}

Transfer Money

{
  "fromAccount": "65d4...",
  "toAccount": "65d5...",
  "amount": 500,
  "idempotencyKey": "unique-key-123"
}

🚀 How to Run

1. Clone the repository:

   git clone <your-repo-url>
   cd BankTransactions

2. Install dependencies:

   npm install

3. Setup Environment Variables: Create a .env file in the root directory and add:

   PORT=3000
   MONGO_URI=your_mongodb_connection_string
   JWT_SECRET=your_jwt_secret
   GMAIL_USER=your_email@gmail.com
   GMAIL_PASS=your_app_password

4. Start the server:

   npm run dev
   # or
   npm start