Account Balance Manager

User Account Balance Management System

Main Features

• Record user transactions for balance updates.
• Retrieve user account balance.

Architecture

The application consists of 2 main components:

1. API Handler

The API Handler manages HTTP requests for retrieving balances and processing user transactions.

API Endpoints

• POST /user/{userId}/transaction - Processes a new transaction for a user.
• GET /user/{userId}/balance - Retrieves the current balance for a specific user.

2. Database

All account balances and transactions are persisted in a PostgreSQL database to ensure consistency and reliability.

Database Schema

---
title: Database Schema
---
erDiagram
   users ||--o{ transactions : "One-to-Many"
   users {
      uint64 userId
      float balance
   }
   transactions {
      string transactionId
      uint64 userId
      float amount
      string source
      datetime createdAt
   }

Build Process

Run the following command to build the application:

make build

Binaries will be available in the build directory.

Entry Points

• API Handler: cmd/api/main.go

Development

Environment Variables

The following environment variables are required to configure the application:

• DATABASE_URL - The Postgres database connection string, e.g., postgres://user:password@host:port/database.

Deployment

Using Docker Compose

Run the following command to deploy the application locally using Docker Compose:

docker-compose up -d

Manual Testing

1. Pre-populated user IDs in the database:
   • 1, 2, 3, 4, 5, 6, 7, 8 and 9.
2. Run the application and use curl to interact with the API. For example:
   • Process a transaction for a user:

     curl -X POST http://localhost:8080/user/1/transaction -H 'Content-Type: application/json' -H "Source-Type: game" -d '{"state": "win", "amount": "50.00", "transactionId": "abc123"}' 
     

   • Retrieve a user's balance:

     curl -X GET http://localhost:8080/user/1/balance
     

Testing

Local Tests

Unit Tests

Execute the following command to run unit tests:

make unit-test

Test Coverage

To generate and view test coverage reports:

• HTML Report:

  make coverage-report
  

• Total Coverage:

  make coverage-total
  

Considerations

• The database and persistence layer have been designed with extensibility in mind, allowing the use of other types of databases as long as they adhere to the required interfaces.
• DAO (Data Access Object) components isolate the business logic from the database and HTTP layers, ensuring a clean and maintainable architecture.
• The HTTP layer (server) is specifically structured to handle request reception, validation, interaction with the DAO, and generating appropriate responses.
• The current implementation is expected to run as a single instance, to guarantee accuracy and consistency in balance calculations. If necessary to horizontally scale, additional design changes would be required.