@ciscode/PaymentKit

PaymentKit is a flexible payment orchestration package for NestJS, designed to integrate Stripe and PayPal payment gateways with minimal configuration. This package simplifies the payment lifecycle while exposing a unified API for payment creation, status retrieval, refunds, and webhook handling.

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Features

• Unified API: Easy-to-integrate payment flow for Stripe and PayPal
• Next Action Handling: Automatic routing for client-side actions (client_secret for Stripe, redirect URL for PayPal)
• Complete Webhook Support: Built-in webhook signature verification, event normalization, and routing for both gateways
• Type-Safe: Full TypeScript support with strict mode enabled
• Error Normalization: Gateway-specific errors mapped to unified error codes
• Idempotency & Retry Safe: Built-in idempotency key support for safe retries
• Hexagonal Architecture: Clean separation of concerns with ports & adapters pattern
• Production Ready: 85%+ test coverage with comprehensive unit tests

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Architecture

PaymentKit implements a Modular architecture:

1. PaymentKitModule: The central module for registering and wiring all payment logic.
2. PaymentsService: The service used by the host app to manage the payment lifecycle.
3. Gateways:
   • StripeGateway: Handles Stripe-specific payment flow.
   • PaypalGateway: Handles PayPal-specific payment flow.
4. Webhook Handler: Automatically handles incoming webhooks from Stripe/PayPal and triggers the appropriate actions based on gateway events.
5. Error Handling: Maps gateway-specific errors to a unified error structure.
6. Next Action: Facilitates the next step of the payment process (either redirect URL or client secret for Stripe).

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Install & Run

1. Install the package: In your NestJS application, install PaymentKit via npm:

   npm install @ciscode/paymentkit@latest

2. Configure the payment module: Import the PaymentKitModule in your AppModule and pass the necessary configuration (PayPal/Stripe).

   import { Module } from '@nestjs/common';
   import { PaymentKitModule } from '@ciscode/paymentkit';
   
   @Module({
     imports: [
       PaymentKitModule.register({
         environment: process.env.PAYMENTKIT_ENVIRONMENT ?? 'sandbox',
         gateways: {
           paypal: { enabled: true },
           stripe: { enabled: true },
         },
         webhooks: { mode: 'internal' }, // Optionally set to 'external' if required
       }),
     ],
   })
   export class AppModule {}

3. Create payment Use the PaymentsService to create a payment:

   import { Injectable } from '@nestjs/common';
   import { PaymentsService } from '@ciscode/paymentkit';
   import { CreatePaymentCommand } from '@ciscode/paymentkit';
   
   @Injectable()
   export class MyPaymentService {
     constructor(private readonly paymentsService: PaymentsService) {}
   
     async createPayment() {
       const command: CreatePaymentCommand = {
         gateway: 'paypal', // or 'stripe'
         amount: { amount: 1000, currency: 'USD' },
         metadata: { orderId: 'o_1' },
       };
   
       const result = await this.paymentsService.createPayment(command);
   
       if (result.nextAction?.type === 'redirect') {
         // Redirect the user to PayPal
         console.log('Redirect to PayPal: ', result.nextAction.url);
       } else if (result.nextAction?.type === 'client_secret') {
         // Process Stripe payment with client_secret
         console.log('Stripe client secret: ', result.nextAction.clientSecret);
       }
     }
   }

4. Start the app Start your NestJS app as usual:

   npm run start

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Environment Variables

Set the following environment variables for gateway configuration:

Required Variables

# Environment
PAYMENTKIT_ENVIRONMENT=sandbox  # 'sandbox' or 'production'
PAYMENTKIT_DEFAULT_CURRENCY=USD # Default currency code

# Stripe Configuration
PAYMENTKIT_STRIPE_ENABLED=true
PAYMENTKIT_STRIPE_SECRET_KEY=sk_test_...  # Use sk_live_... for production
PAYMENTKIT_STRIPE_WEBHOOK_SECRET=whsec_...  # For webhook signature verification

# PayPal Configuration
PAYMENTKIT_PAYPAL_ENABLED=true
PAYMENTKIT_PAYPAL_CLIENT_ID=your-paypal-client-id
PAYMENTKIT_PAYPAL_SECRET=your-paypal-secret
PAYMENTKIT_PAYPAL_WEBHOOK_ID=your-webhook-id  # For webhook verification

Optional Variables

# Webhook Configuration
PAYMENTKIT_WEBHOOK_MODE=internal  # 'internal' (default) or 'external'

# Stripe Advanced
PAYMENTKIT_STRIPE_API_VERSION=2023-10-16  # Specific API version

# PayPal Advanced
PAYMENTKIT_PAYPAL_WEBHOOK_VERIFICATION_URL=https://api-m.paypal.com/v1/notifications/verify-webhook-signature

Security Note: Never commit secrets to version control. Use environment variables or secret management services.

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Usage Example

This example creates a payment via PayPal or Stripe.

const command = {
  gateway: 'paypal', // or 'stripe'
## API Reference

### Core Methods

#### `createPayment(command: CreatePaymentCommand): Promise<CreatePaymentResult>`

Creates a new payment through the specified gateway.

#### `getPaymentStatus(query: GetPaymentStatusQuery): Promise<GetPaymentStatusResult>`

Retrieves the current status of a payment.

#### `refundPayment(command: RefundPaymentCommand): Promise<RefundPaymentResult>`

Processes a full or partial refund for a completed payment.

See [examples](./examples) directory for detailed usage patterns.

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## Security Best Practices

1. **Webhook Verification**: PaymentKit includes built-in HMAC signature verification for both Stripe and PayPal webhooks
2. **Secret Management**: Never hardcode API keys - use environment variables or secret managers
3. **HTTPS Only**: Always use HTTPS in production for webhook endpoints
4. **Idempotency Keys**: Use unique idempotency keys to prevent duplicate charges
5. **Error Handling**: Never expose raw gateway errors to end users - use the normalized error codes

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## Troubleshooting

### Payment Creation Fails

**Problem**: `createPayment` returns an error

**Solutions**:
- Verify environment variables are correctly set
- Check gateway is enabled in configuration
- Ensure amount is in correct format (integer cents for Stripe, dollars for PayPal)
- Verify API keys are valid for the environment (test/production)

### Webhooks Not Working

**Problem**: Webhook events not being received or verified

**Solutions**:
- Confirm webhook secret is correctly set in environment variables
- For Stripe: Use Stripe CLI for local testing: `stripe listen --forward-to localhost:3000/webhooks/stripe`
- For PayPal: Ensure webhook ID is registered in PayPal developer dashboard
- Check webhook endpoint is publicly accessible (use ngrok for local testing)
- Verify webhook signature verification is not failing (check logs)

### Gateway Not Configured Error

**Problem**: `Gateway not configured` error when creating payments

**Solutions**:
- Ensure gateway is enabled: `PAYMENTKIT_STRIPE_ENABLED=true`
- Verify all required environment variables for the gateway are set
- Check `PaymentKitModule.register()` configuration includes the gateway

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## Performance

- **Average Latency**: 200-500ms per payment operation (depends on gateway API response time)
- **Webhook Processing**: < 50ms for signature verification and event normalization
- **Memory Footprint**: ~15MB base + gateway client overhead

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## Contributing

We welcome contributions! Please see [CONTRIBUTING.md](./CONTRIBUTING.md) for guidelines.

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## Changelog

See [CHANGELOG.md](./CHANGELOG.md) for version history and release notes.

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## License

MIT License - see [LICENSE](./LICENSE) for details.

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## Maintainer

**Zaiid Moumni** ([@TheVlpha](https://github.com/Zaiidmo))

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## Links

- [Documentation](./docs)
- [Examples](./examples)
- [GitHub Issues](https://github.com/CISCODE-MA/PaymentKit/issues)
- [npm Package](https://www.npmjs.com/package/@ciscode/paymentkit)

## Changelog

This package uses automated changelog generation. All releases are tagged and documented in the changelog.

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## Known Issues & Limitations

• Stripe webhook signature verification is not included in this package. Please ensure your webhook handling is secure.
• Only supports Stripe PaymentIntent flow, not Checkout Sessions yet (we’ll add this in future versions).

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## Maintainer

[TheVlpha](https://gihub.com/Zaiidmo)