💰 Coinly – Expense Tracker

Coinly is a full-stack Next.js-based Financial Web Application built using React and Tailwind CSS.

It allows users to track their personal debts, manage IOUs, and maintain a clear ledger of financial transactions with secure authentication and a modern UI.

The project demonstrates strong fundamentals in Full-Stack Development, NoSQL database design, secure server actions, and responsive layout.

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🔗 Live Demo (Deployed)

➡️ See Coinly in action: https://coinly0203.vercel.app/

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🚀 Key Features

🔐 Authentication & Security

• Secure User Registration & Login (JWT & bcrypt)
• Robust Input Validation using Zod
• Protection against NoSQL Injection vulnerabilities

✅ Debt & Ledger Management (CRUD)

• Create new IOU transactions (Borrow/Lend)
• Repay debts and track partial settlements
• View detailed ledger balances opening and closing across transactions
• Manage contacts and their associated debts

📂 Transaction Viewing & Filtering

• View all active debts and IOUs
• Filter and review settled vs pending balances
• Detailed transaction history per contact

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🧠 System Design Overview

• Architecture: Next.js App Router (React Server Components & Server Actions)
• Authentication: Custom JWT Authorization
• Database Design: MongoDB (NoSQL) with Strict Mongoose Schemas
• UI: Responsive, mobile-first design using Tailwind CSS

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🛠️ Tech Stack

• Programming Language: TypeScript
• Framework: Next.js
• Frontend: React, Tailwind CSS
• Database: MongoDB (Mongoose)
• Validation: Zod
• Version Control: Git & GitHub

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🏗️ Project Structure

coinly/
├── src/
│   ├── app/                 # Next.js App Router (pages, layouts, auth/API logic)
│   ├── actions/             # Next.js Server Actions (ledger calculations, DB queries)
│   ├── components/          # Reusable UI components (IOUContactCard, modals, etc.)
│   ├── models/              # Mongoose database schemas (User, Contact, Entry)
│   └── lib/                 # Utility functions and database connection
├── package.json             # Project dependencies and scripts
└── tailwind.config.ts       # Tailwind CSS configuration

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🧩 Models

1️⃣ User Model

• Handles secure authentication and user profiles.

2️⃣ Contact Model

• Represents individuals with whom the user has financial transactions.
• Tracks contact info and real-time overall balance.

3️⃣ Entry/Transaction Model

• Represents individual debt creation or repayment transactions.

Relationship:

• One-to-Many
  • 1 User ➝ Multiple Contacts
  • 1 Contact ➝ Multiple Transactions

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⚙️ Installation & Setup

1. Clone the repository

git clone https://github.com/your-username/coinly.git
cd coinly

2. Install dependencies

npm install

3. Set up environment variables Create a .env.local file in the root directory and configure your MongoDB URI and JWT Secret:

MONGODB_URI=your_mongodb_connection_string
JWT_SECRET=your_jwt_secret

4. Run the development server

npm run dev

5. Open browser and visit:

http://localhost:3000/

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📌 Future Improvements

• Multi-currency support
• Data export functionality (CSV/PDF)
• Dark mode configuration
• Financial charts and analytics

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🤝 Contributing

• Contributions, issues, and feature requests are welcome!
• Feel free to fork this repo and submit pull requests.

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📜 License

• This project is open-source and available under the MIT License