How would you design a Payment Gateway integration that supports multiple providers (PayPal, Stripe)?

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Accepted Answer

I would define an application-level payment abstraction and implement one adapter per provider. The business layer should work with our own PaymentRequest and PaymentResult models rather than provider-specific SDK types. A factory or dependency-injection strategy can select the appropriate provider. This isolates vendor-specific APIs and makes adding another provider much safer. public interface IPaymentGateway
{
 Task ChargeAsync(PaymentRequest request);
}

public class StripeGateway : IPaymentGateway
{
 public Task ChargeAsync(PaymentRequest request)
 {
 // Map domain request to Stripe API.
 return Task.FromResult(new PaymentResult(true));
 }
}

public class PayPalGateway : IPaymentGateway
{
 public Task ChargeAsync(PaymentRequest request)
 {
 // Map domain request to PayPal API.
 return Task.FromResult(new PaymentResult(true));
 }
}

public class PaymentService
{
 private readonly IPaymentGateway gateway;

public PaymentService(IPaymentGateway gateway)
 {
 this.gateway = gateway;
 }

public Task PayAsync(PaymentRequest request)
 => gateway.ChargeAsync(request);
} Use an abstraction owned by the application rather than exposing provider SDK types. Use Adapter implementations to translate provider-specific APIs. Select providers through dependency injection, configuration, routing policy, or a factory. Normalize provider errors into meaningful application-level error categories. Design for idempotency because payment requests may be retried. Handle webhooks, asynchronous payment states, timeouts, retries, reconciliation, and duplicate notifications. Never assume a successful API response alone means the entire payment lifecycle is complete.

How would you design a Payment Gateway integration that supports multiple providers (PayPal, Stripe)?

Provider-Agnostic Payment Gateway Design

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