Expense Tracker API

A backend API for personal expense management, built to demonstrate Clean Architecture, solid backend design, and practical engineering decisions commonly used in production systems.

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Project Overview

Expense Tracker API provides a robust backend for managing personal finances. The system allows users to:

• record and manage expenses,
• organize spending by categories,
• analyze expenses using aggregated statistics over monthly or custom time ranges.

The primary focus of this project is not only functionality, but also code structure, maintainability, and correctness, reflecting real-world backend development requirements.

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Technical Stack

• Language: Go 1.21+
• HTTP Framework: Gin
• ORM: GORM
• Database: PostgreSQL
• Authentication & Authorization: JWT
• Logging: Zap (structured, leveled logging)
• API Documentation: Swagger / OpenAPI
• Containerization: Docker & Docker Compose
• Testing: Go testing tools with unit test coverage

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Core Functionality

• Secure JWT-based authentication and role-aware authorization
• Full CRUD lifecycle for expense entities
• Category-based expense classification
• Pagination and filtering for efficient data access
• Request validation with consistent, structured error responses

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Analytics & Reporting

• Monthly expense summaries
• All-time aggregated spending totals
• Custom date range analytics with daily breakdowns
• Server-side aggregation optimized at the database level

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Architecture & Engineering Practices

The application is structured according to Clean Architecture principles:

• Handler layer — HTTP request handling, validation, and response mapping
• Service layer — business rules, use cases, and orchestration logic
• Repository layer — database abstraction and query implementation

This design:

• decouples business logic from infrastructure concerns,
• improves testability and readability,
• allows easy replacement of frameworks or persistence layers.

Additional engineering highlights:

• custom domain-level error types with proper HTTP status mapping,
• centralized configuration management,
• database migrations for schema version control,
• structured logging for observability and debugging,
• unit tests focused on core business logic rather than transport details.

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Project Structure

cmd/            – application entry point
internal/
  handler/      – HTTP handlers (presentation layer)
  service/      – business logic (use cases)
  repository/   – data access layer
  model/        – domain models
  middleware/   – authentication, logging
migrations/     – database schema migrations
docs/           – Swagger / OpenAPI specification

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Running the Project

Using Docker

docker-compose up -d

Running locally

go mod download
go run cmd/main.go migrate
go run cmd/main.go

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API Documentation

Interactive Swagger UI is available at:

http://localhost:8080/swagger/index.html

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This project was built as part of my professional portfolio to demonstrate backend engineering skills with Go, with a strong emphasis on architecture, clean code, and production readiness.

Best regards, Mykola