SmartExpense API 💸

SmartExpense is a secure, robust, and intelligent REST API for personal expense tracking. Built with Spring Boot, it allows users to manage their finances, set budgets, and gain insights into their spending habits.

This is a backend-only, portfolio project demonstrating a modern Java tech stack, secure API practices, and advanced business logic.

---

✨ Key Features

• Secure Authentication: Full user registration and login system using Spring Security and JWT (JSON Web Tokens).
• Secure Endpoints: All endpoints are protected. Users can only create, read, update, or delete their own expenses and categories.
• Data Aggregation: A GET /api/summary/monthly endpoint that performs server-side calculations to return a full monthly report (total spending, top category, and a complete category breakdown).
• Real-time Budget Alerts: Users can set a monthly budget. When adding a new expense, the API checks the total spending in real-time and returns a budgetWarning if the user has exceeded their limit.
• Advanced Filtering: The GET /api/expenses endpoint can be dynamically filtered by date range or by category.
• Custom Exception Handling: A professional, global exception handler (@RestControllerAdvice) provides clean, safe, and consistent JSON error messages for all API errors (e.g., 404 Not Found, 400 Bad Request).

---

🛠️ Technology Stack

• Framework: Spring Boot
• Security: Spring Security, JWT
• Database: Spring Data JPA, MySQL
• Testing: H2 Database (for in-memory testing)
• Build: Maven
• Utilities: Lombok, jakarta.validation

---

🚀 API Endpoints

A high-level overview of the core API endpoints.

Method	Endpoint	Description
POST	/api/auth/register	Register a new user.
POST	/api/auth/login	Log in and receive a JWT.
GET	/api/expenses	Get all expenses (with filters).
POST	/api/expenses	Add a new expense.
PUT	/api/expenses/{id}	Update an expense.
DELETE	/api/expenses/{id}	Delete an expense.
GET	/api/categories	Get all user-created categories.
POST	/api/categories	Create a new category.
PUT	/api/user/budget	Set the user's monthly budget.
GET	/api/summary/monthly	Get the full summary for a given month.

---

🔮 Future Implementation

• Recurring Expenses: A @Scheduled job to automatically add recurring expenses (e.g., "Netflix") every month.
• Data Export: A GET /api/export/csv endpoint to download a complete CSV file of monthly expenses.