Loan Fintech API with Django REST Framework

Objective

The main objective of this project is to create an API to manage the loan payments control system from a fintech.

Purpose

The purpose of this challenge is to test your ability to implement a solution given an abstract problem. You may find a problem in the asked task that you need to explain the problem and propose a solution to fix it.

Problem

A fintech needs to keep track of the amount of money loaned and the missed/made payments. It also needs a place to retrieve the volume of outstanding debt at some point in time.

Limitations

Loans are paid back in monthly installments.

Install

Setup install

• pipenv install

Running

• python manage.py makemigrations --settings=config.settings.dev
• python manage.py migrate --settings=config.settings.dev
• python manage.py test --settings=config.settings.dev
• python manage.py runserver --settings=config.settings.dev

Endpoints

• Documentatin: /swagger/
• Admin: /admin/
• Get JWT token: /api/token/
• Refresh JWT token: /api/token/refresh/
• All clients: /clients/
• Client by id: /client/{client_id}/
• All loans: /loans/
• Balance by client id: /loans/{loan_id}/balance/
• Payments by client id: /loans/{loan_id}/payments/

POST /clients/

Summary

Create a record of a client

Payload

• client_id:
• name:
• surname:
• email:
• telephone:
• cpf:

Example of sent data

{
    "client_id": 1,
    'name': 'Nome',
    'surname': 'Sobrenome',
    'email': 'nome@gmail.com',
    'telephone': '6533245152',
    'cpf': '85478999988'
}

GET /client/

Summary

List client id

Example of sent data

{
    "client_id": 1,
}

Example of received data

{
    "client_id": 1,
    'name': 'Nome',
    'surname': 'Sobrenome',
    'email': 'nome@gmail.com',
    'telephone': '6533245152',
    'cpf': '85478999988'
}

POST /loans

Summary

Create a loan application. Loans are automatically accepted.

Payload

• amount: loan amount in dollars.
• term: number of months that will take until the loan gets paid-off.
• rate: interest rate as decimal.
• date: when the loan was requested (origination date as an ISO 8601 string).

Example of sent data

{
    "amount": 1000,
    "term": 12,
    "rate": 0.05,
    "date": "2019-05-09 03:18Z"
}

Reply

• loan_id: unique id of the loan.
• installment: monthly loan payment.

Example of received data

{
    "loan_id": "000-0000-0000-0000"
    "installment": 85.60
}

Notes

Loan payment formula

r = rate / 12
installment = [r + r / ((1 + r) ^ term - 1)] x amount

Example

For repaying a loan of $1000 at 5% interest for 12 months, the equation would be:

installment = [(0.05 / 12) + (0.05 / 12) / ((1 + (0.05 / 12)) ^ 12 - 1] x 1000
installment = 85.60

POST /loans/<:id>/payments

Summary

Create a record of a payment made or missed.

Payload

• payment_choice: type of payment: made or missed.
• date: payment date.
• amount: amount of the payment made or missed in dollars.

Example of sent data (Payment made)

{
    "payment_choice": "made",
    "date": "2019-05-07 04:18Z",
    "amount": 85.60
}

Example of sent data (Payment missed)

{
    "payment_choice": "missed",
    "date": "2019-05-07 04:18Z",
    "amount": 85.60
}

POST /loans/<:id>/balance

Summary

Get the volume of outstanding debt (i.e., debt yet to be paid) at some point in time.

Payload

• date: loan balance until this date.

Example of sent data

{
    "date": "2017-09-05 02:18Z"
}

Reply

• balance: outstanding debt of loan.

Example

{
    "balance": 40
}