Card Validator API

A clean and robust API for validating card numbers using the Luhn algorithm, built with NestJS and TypeScript.

Features

• Luhn Algorithm Validation: Accurate validation of credit/debit card numbers.
• Card Type Detection: Basic identification of Visa, MasterCard, Amex, and Discover.
• Swagger Documentation: Interactive API docs available at /api/docs.
• Strict TypeScript: Configured with strict: true for maximum type safety.
• HNG Standard Response Format: All responses are wrapped in a consistent { message, data } structure.
• Global Error Handling: Standardized error responses with appropriate HTTP status codes.
• DTO Validation: Input validation using class-validator and class-transformer.

Architecture Choice

The project follows a modular structure inspired by clean architecture principles:

• Modules: Logic is encapsulated into feature-specific modules (e.g., CardValidatorModule).
• Service Layer: Orchestrates business logic (Luhn validation).
• Controller Layer: Handles HTTP requests and uses DTOs for input validation.
• Common Layer: Contains cross-cutting concerns like Interceptors and Decorators.
• Interceptors: ResponseTransformInterceptor ensures all responses follow the mandatory HNG SDK format.

Technology Stack

• Framework: NestJS (Node.js)
• Language: TypeScript
• Validation: class-validator
• Testing: Jest

Setup and Installation

Prerequisites

• Node.js (v18 or higher)
• npm or yarn

Installation

# Clone the repository
git clone <repository-url>

# Navigate to project directory
cd card-validator-api

# Install dependencies
npm install

Running the Project

# Development mode
npm run start:dev

# Production mode
npm run start:prod

Running Tests

# Unit tests
npm run test

API Base URLs

• API Root: http://localhost:3000
• API Version 1: http://localhost:3000/api/v1
• Interactive Documentation (Swagger): http://localhost:3000/api/docs

Test Card Numbers

You can use the following numbers to test the API's validation logic:

Status	Card Type	Card Number
Valid	Visa	4242424242424242
Valid	Mastercard	5105105105105100
Valid	Discover	6011111111111117
Valid	Amex	378282246310005
Invalid	Any	4242424242424241 (Fails Luhn)
Invalid	Too Short	12345678901 (Less than 12 digits)

API Documentation

Validate Card Number

Endpoint: POST /api/v1/validate-card

Request Body:

{
  "card_number": "799273987130"
}

Success Response (Valid Card):

• Status Code: 201 Created

{
  "message": "Card number is valid",
  "data": {
    "is_valid": true,
    "card_type": "unknown"
  }
}

Success Response (Invalid Card):

• Status Code: 201 Created

{
  "message": "Card number is invalid",
  "data": {
    "is_valid": false,
    "card_type": "visa"
  }
}

Error Response (Bad Request):

• Status Code: 400 Bad Request

{
  "statusCode": 400,
  "message": [
    "Card number must be at least 12 digits and Card number must not exceed 19 digits"
  ],
  "error": "Bad Request"
}

Implementation Decisions

1. NestJS: Chosen for its robust architectural patterns, dependency injection, and excellent TypeScript support, which aligns with the requirement for strict mode.
2. Response Wrapping: Implemented via a Global Interceptor to ensure consistency across the entire API without cluttering controllers.
3. Luhn Algorithm: Used as the primary validation logic as it is the industry standard for verifying the checksum of identification numbers.
4. Validation Pipes: Used ValidationPipe with whitelist: true to prevent unwanted properties and ensure data integrity.

Author

• Chris

License

This project is licensed under the MIT License.