💸 FinTech Solutions Backend Challenge

🚀 Project Overview

This repository contains a backend solution for the technical challenge proposed by FinTech Solutions Inc.. The goal is to build two API services in Go:

1. Migration Service (POST /migrate)
   Uploads and processes historical transaction data from CSV files into a PostgreSQL database.

2. Balance Service (GET /users/{user_id}/balance)
   Retrieves a user's balance summary, with optional date filtering.

The system is designed to be robust, scalable, and easy to deploy locally using Docker.

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🏗️ Architecture and Design Patterns

The project follows a layered architecture to promote separation of concerns and modularity:

• Presentation Layer (Handlers): Handles HTTP requests and delegates logic to services.
• Service Layer (Business Logic): Encapsulates core rules like CSV parsing and balance calculations.
• Repository Layer (Data Access): Abstracts database operations using the Repository Pattern.

✅ SOLID Principles

• SRP: Each component has a single responsibility.
• DIP: Services depend on interfaces, not concrete implementations.

🧩 Additional Patterns

• Repository Pattern: Decouples persistence from business logic.
• Service Layer Pattern: Keeps transport logic (HTTP) separate from core rules.

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🛠️ Technologies Used

• Language: Go (Golang)
• Database: PostgreSQL
• Containers: Docker & Docker Compose
• Libraries:
  • go-chi/chi — HTTP routing
  • rs/zerolog — Structured logging
  • sethvargo/go-envconfig — Environment config
  • pgx & database/sql — PostgreSQL drivers
  • encoding/csv — CSV parsing
  • swaggo/swag — Swagger documentation

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🚀 Getting Started

▶️ Prerequisites

• Docker & Docker Compose installed

▶️ Run with Docker

git clone https://github.com/Sirpyerre/fintech-backend.git
cd fintech-backend
docker-compose up --build

The API will be available at:
http://localhost:8080

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📖 API Documentation

🔄 Migration Service

POST /migrate

• Upload a CSV file with transactions.
• Header: Content-Type: multipart/form-data
• Field name: file
• Expected columns: id,user_id,amount,datetime

💰 Balance Service

GET /users/{user_id}/balance

• Returns balance, total credits, and total debits.

Optional query params:

• from: Start date (RFC3339)
• to: End date (RFC3339)

✅ Sample Response

{
  "balance": 25.21,
  "total_debits": 10,
  "total_credits": 15
}

📎 Swagger UI: /swagger/index.html

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📊 Observability

• Structured logging with zerolog

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🧪 Testing

Run unit tests for services:

go test ./internal/services/...

Includes coverage for:

• Migration logic
• Balance calculations
• Error handling

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🧠 Future Improvements

• Add Redis caching for frequent balance queries
• Improve CSV validation and error reporting
• Add integration tests with real DB
• Implement graceful shutdown and health checks
• Extend Swagger with response examples and error codes

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📄 License

MIT — free to use, modify, and share.