Purple Bank

Overview

Purple Bank is a REST-based API designed to do checks and balances. It only accepts and responses contents in JSON format.

With Purple Bank API, you can:

• Create User
• Get User State
• Create transactions

Resources

User

User entity represents a Purple Bank account. A User can have many Transactions.

Field	Type	Description
id	uuid	A key that uniquely identifies the User
name	string	The user name
balance	bigdecimal	The user total balance
transactions	vector	A vector containing user's transactions

Transaction

Transaction entity represents a monetary transaction. A Transaction must belongs to a User.

Field	Type	Description
id	uuid	A key that uniquely identifies the Transaction
operation	string ["credit" "debit"]	The transaction operation
amount	number	The transaction amount
timestamp	string	The timestamp of transaction creation

API Endpoints

Creating User

To create a new user, make a POST request on /users passing user attributes on request body.

POST /users/

Example request body

{
  "name": "Joao"
}

Example response body (201)

{
    "id": "82b9a195-e8de-4cdf-8a8d-ce79e1dd264b",
    "name": "Joao",
    "balance": 0,
    "transactions": []
}

Response Status Codes

Status Code	Meaning
201	User was created
400	Invalid user params

Getting User

To retrieve a user, make a GET request on /users/:user-id passing the user id as path-param.

GET /users/:user-id

Example response body (200)

{
    "id": "276b17a0-fa61-431e-ab8f-1049a5afa7ba",
    "name": "Paulo",
    "balance": 0,
    "transactions": []
}

Response Status Codes

Status Code	Meaning
200	User was found
404	User not found

Creating Transaction

To creates a new transaction, make a POST request on /users/:user-id/transaction passing the user id as path-param and transaction attributes on request body.

POST /users/:user-id/transactions

Example request body

{  
   "operation": "credit",
   "amount": 20.50
}

Example response body (201)

{
    "id": "13409d68-dfee-431a-beb1-c5553a96663e",
    "operation": "credit",
    "amount": 20.50,
    "timestamp": "2019-06-07T07:25:06.561Z"
}

Response Status Codes

Status Code	Meaning
201	Transaction was created
400	Invalid transaction params
403	User has not enough balance
404	User not found

Running the application

To run the platform in production mode, execute lein run command on terminal.

To run it in development mode, execute lein run-dev command on terminal.

You can also run it from REPL executing (-main) for production mode or (run-dev) for development mode.

Tests

The project is using Midje and selvage to implement unit and integration tests. The tests has full coverage of adapters, controller and logic code.

To run the test pipeline, execute lein midje command on terminal.

You can also run it from REPL executing (do (use 'midje.repl) (load-facts)).

System Design

I've decided to use hexagonal architecture on this project for three main reasons:

• Isolate the application core (controller and logic) from services to write automated tests that coverages the whole code.
• Make it easy to couple and decouple services according to the needs.
• Get closer to microservices development mindset at Nubank's daily work.

Components

I've decided to use Components framework because it makes possible to have stateful resources in a functional paradigm and also it fits very well on hexagonal architecture concepts, allowing to easily couple and decouple new ports.

• Config: Holds environment configurations.
• Logger: Port component responsible for system logging. It uses a different implementation according to running environment, such as:
  • Debug-Logger on development/test mode to log received events and data.
  • Logger on production mode to log only received events for data privacy purposes. In a real application, it could send logs to Datadog, for example.
• Storage: Port component responsible for system storage. It uses InMemoryStorage implementation to any environment.
• Routes: Encapsulates pedestal http routes.
• Service: Builds pedestal service configurations according to running environment.
• Servlet: Port component responsible for http server. It creates a pedestal server from service component and only starts it if running environment is development or production.

To make sure that services can be easily changed, its implementations must defines a protocol that specifies the needed functions. In our case:

• Logger components must defines logger-client protocol and its functions.
• Storage components must defines storage-client protocol and its functions.

Controller Results

The concept behind controller result is to provide a default schema to be used on communications between adapters and controllers. It allows to each adapter handles the response coming from the controller actions in their own way.

A controller result is a map data structure that contains :data and :error keys.

Whenever a controller action is successful, it must associates the resulted data to :data key, nil value to :error key and returns the result map. If the action is unsuccessful, it must associate the reason as keyword to :error, nil value to :data and returns the result map.