Credify

A production-ready REST API for customer onboarding and loan underwriting. It supports customer registration, loan eligibility checks, loan creation, and viewing loans. All identifiers (customer_id, loan_id) are UUIDs.

• Framework: Django 5 + Django REST Framework
• DB: PostgreSQL (Dockerized)
• Python: 3.13 (container)
• IDs: UUIDs
• EMI calculation: Compound interest (monthly)

Features

• Register customers with approved credit limits
• Compute credit score and return corrected interest when needed
• Create loans if eligible and persist them
• View a loan by ID and list all loans for a customer
• Robust validation and error handling with proper HTTP status codes

Quick Start

Prerequisites

• Docker and Docker Compose (recommended)
• Or: Python 3.12+, PostgreSQL 14+ (for local runs)

Environment

Create a .env in the project root (used by docker-compose and settings):

POSTGRES_DB=alemno_db
POSTGRES_USER=alemno
POSTGRES_PASSWORD=supersecret

Run with Docker

docker compose up --build

• API base URL: http://localhost:8000

Run locally (without Docker) on Windows (PowerShell)

python -m venv .venv
.\.venv\Scripts\Activate.ps1
pip install -r src\requirements.txt

$env:POSTGRES_DB="alemno_db"
$env:POSTGRES_USER="alemno"
$env:POSTGRES_PASSWORD="supersecret"
$env:POSTGRES_HOST="localhost"
$env:POSTGRES_PORT="5432"

cd src
python manage.py migrate
python manage.py runserver 8000

Project Structure

src/
    alemno/                # Django project settings/urls/wsgi
    core/                  # App: models, serializers, views, urls
    services/              # Business logic (eligibility, scoring, creation)
    entrypoint.sh          # Container entrypoint running migrations + server
    manage.py
Dockerfile
docker-compose.yml

Data Model (simplified)

• Customer

  • customer_id (UUID, PK)
  • first_name, last_name, age, phone_number
  • monthly_income (Decimal)
  • approved_limit (Decimal): 36 × monthly_income, rounded to nearest lakh (100,000)

• Loan

  • loan_id (UUID, PK)
  • customer (FK → Customer)
  • loan_amount (Decimal)
  • tenure (months, int)
  • interest_rate (annual %, Decimal)
  • monthly_payment (Decimal)
  • emis_paid_on_time (int)
  • date_of_approval, end_date (dates)

API Overview

Base URL: http://localhost:8000

1) Register a customer

POST /register

Request

{
    "first_name": "John",
    "last_name": "Doe",
    "age": 30,
    "monthly_income": 50000,
    "phone_number": "9876543210"
}

Response 201 Created

{
    "customer_id": "550e8400-e29b-41d4-a716-446655440000",
    "name": "John Doe",
    "age": 30,
    "monthly_income": 50000.0,
    "approved_limit": 1800000.0,
    "phone_number": "9876543210"
}

2) Check loan eligibility

POST /check-eligibility

Request

{
    "customer_id": "550e8400-e29b-41d4-a716-446655440000",
    "loan_amount": 500000,
    "interest_rate": 10.5,
    "tenure": 36
}

Response 200 OK (example)

{
    "customer_id": "550e8400-e29b-41d4-a716-446655440000",
    "approval": true,
    "interest_rate": 10.5,
    "corrected_interest_rate": 10.5,
    "tenure": 36,
    "monthly_installment": 16134.33
}

3) Create a loan

POST /create-loan

Request

{
    "customer_id": "550e8400-e29b-41d4-a716-446655440000",
    "loan_amount": 500000,
    "interest_rate": 10.5,
    "tenure": 36
}

Response 201 Created (approved)

{
    "loan_id": "660e8400-e29b-41d4-a716-446655440001",
    "customer_id": "550e8400-e29b-41d4-a716-446655440000",
    "loan_approved": true,
    "message": "Loan approved",
    "monthly_installment": 16134.33
}

4) View a loan by ID

GET /view-loan/{loan_id}

Response 200 OK (example)

{
    "loan_id": "660e8400-e29b-41d4-a716-446655440001",
    "customer": {
        "id": "550e8400-e29b-41d4-a716-446655440000",
        "first_name": "John",
        "last_name": "Doe",
        "phone_number": "9876543210",
        "age": 30
    },
    "loan_amount": 500000.0,
    "interest_rate": 10.5,
    "monthly_installment": 16134.33,
    "tenure": 36
}

5) View all loans for a customer

GET /view-loans/{customer_id}

Response 200 OK (list)

[
    {
        "loan_id": "660e8400-e29b-41d4-a716-446655440001",
        "loan_amount": 500000.0,
        "interest_rate": 10.5,
        "monthly_installment": 16134.33,
        "repayments_left": 36
    }
]

Financial Notes

• EMI uses monthly compounding: r = (annual_rate/100)/12. Uses Decimal internally.
• approved_limit = 36 × monthly_income, rounded to nearest lakh (100,000).

Troubleshooting

• Postgres not ready: docker compose waits on DB healthcheck; if flapping, run docker compose down -v && docker compose up --build.
• DisallowedHost: ensure ALLOWED_HOSTS in settings includes your host.
• Migrations on start: container entrypoint runs python manage.py migrate automatically.
• Port conflict: change "8000:8000" in docker-compose.

Production Tips

• Set strong SECRET_KEY, disable DEBUG, set ALLOWED_HOSTS properly.
• Run behind a reverse proxy (Nginx) and serve via Gunicorn/Uvicorn.
• Use managed Postgres, enable backups, monitor connections.
• Apply migrations in CI/CD before deploy.
• Configure structured logging to stdout or a sink.

Contributing

1. Fork the repository
2. Create a feature branch
3. Add tests for changes
4. Open a pull request with context

License

Add a license file (e.g., MIT) at the repo root.