🚀 Transaction Statistics API

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🇺🇸 Overview

This project is a high-performance REST API built to process financial transactions and compute real-time statistics based on the last 60 seconds.

Developed as part of Itaú backend engineering challenge, the system focuses on:

• Performance (in-memory processing)
• Clean architecture
• Thread safety
• Real-time computation

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🇧🇷 Visão Geral

Este projeto é uma API REST de alta performance para processamento de transações financeiras e cálculo de estatísticas em tempo real com base nos últimos 60 segundos.

O foco foi:

• Performance (dados em memória)
• Código limpo
• Concorrência segura
• Cálculo em tempo real

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🧰 Tech Stack

• Java 17
• Spring Boot
• Maven
• JUnit / MockMvc
• ConcurrentLinkedDeque

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📡 API Endpoints

➕ POST /transacao

Creates a new transaction

{
  "valor": 100.0,
  "dataHora": "2026-04-16T20:00:00-03:00"
}

Responses:

• 201 Created → Success
• 422 Unprocessable Entity → Invalid data
• 400 Bad Request → Malformed JSON

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🧹 DELETE /transacao

Clears all transactions

• 200 OK

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📊 GET /estatistica

Returns statistics from last 60 seconds

{
  "count": 5,
  "sum": 500.0,
  "avg": 100.0,
  "min": 50.0,
  "max": 200.0
}

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⚙️ How to Run

./mvnw spring-boot:run

App runs at:

http://localhost:8080

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🧪 Running Tests

./mvnw test

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🧠 Architecture

• Controller → handles HTTP layer
• Service → business rules
• DTO → validation and transport
• Model → core data

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⚡ Performance Strategy

• In-memory storage (no DB)
• O(n) filtering limited to 60 seconds
• Thread-safe structure (ConcurrentLinkedDeque)
• Zero I/O bottlenecks

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🛡️ Error Handling

• Global exception handler (@RestControllerAdvice)
• Proper HTTP status codes
• Clear error responses

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👨‍💻 Author

Caíque

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⭐ Final Thoughts

This project demonstrates the ability to design and implement a robust backend system under constraints, focusing on performance, clarity, and real-world engineering practices.

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