🏦 Account Ledger System

A backend system that simulates a banking-style ledger architecture for managing accounts and transactions.
This project focuses on secure financial record management, atomic transactions, and ledger-based balance tracking.

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🚀 Features

🔐 Authentication

• User Registration
• User Login
• User Logout
• JWT-based authentication
• Cookie-based session management
• Token blacklist system for secure logout

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👤 Account Management

• Create user accounts
• Multiple accounts per user
• Account status management:
  • ACTIVE
  • FROZEN
  • CLOSED

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📊 Ledger-Based Accounting

Instead of storing balance directly, the system calculates balance using ledger entries.

Ledger entries include:

• DEBIT
• CREDIT

This follows real banking system architecture where balance is derived from transactions.

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💸 Transaction System

Users can transfer funds between accounts.

Features include:

• Account validation
• Balance validation
• Account status verification
• Idempotent transactions (prevents duplicate payments)

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🔁 Idempotency

Each transaction uses an idempotency key to prevent duplicate processing.

This ensures:

• Safe retries
• Duplicate payment protection

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🔄 Atomic Transactions (MongoDB Sessions)

Transactions are executed using MongoDB sessions to ensure atomicity.

Steps:

1. Create transaction (PENDING)
2. Create debit ledger entry
3. Create credit ledger entry
4. Mark transaction as COMPLETED

If any step fails → the transaction is rolled back.

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📧 Email Notifications

Email notifications are sent for:

• User Registration
• Successful Transactions
• Failed Transactions

Implemented using Nodemailer with OAuth2 authentication.

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🛠 Tech Stack

• Node.js
• Express.js
• MongoDB
• Mongoose
• JWT Authentication
• bcryptjs
• Nodemailer
• MongoDB Transactions (Sessions)

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🔒 Security Features

• Password hashing using bcrypt
• JWT authentication
• Cookie-based sessions
• Token blacklist system
• Idempotent transactions
• Account status validation

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🎯 Key Learning Concepts

This project demonstrates:

• Ledger based accounting systems
• Financial transaction integrity
• Idempotency patterns
• MongoDB transactions
• Secure authentication systems
• Backend architecture design

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📌 Future Improvements

• Transaction history API
• Account freeze/unfreeze API
• Admin dashboard
• Rate limiting
• Frontend dashboard (React)

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👨‍💻 Author

Tauseef Ahmad