Architecture Tour

// PaymentProcessor Interface - Extensible for 40+ providers
public interface PaymentProcessor {
    PaymentMethod getMethod();
    boolean supports(PaymentRequest request);
    PaymentResult process(PaymentRequest request);
}

// Processor Registry - Hot-reloadable configuration
@Service
public class ProcessorRegistry {
    private final Map<PaymentMethod, PaymentProcessor> processors;

    public PaymentResult route(PaymentRequest request) {
        return processors.values().stream()
            .filter(p -> p.supports(request))
            .findFirst()
            .map(p -> p.process(request))
            .orElseThrow(() -> new UnsupportedPaymentException());
    }
}

// Example: MoMo Processor Implementation
@Component
public class MoMoProcessor implements PaymentProcessor {
    @Override
    public PaymentMethod getMethod() { return PaymentMethod.MOMO; }

    @Override
    public PaymentResult process(PaymentRequest req) {
        // 1. Build signature with HMAC-SHA256
        // 2. Call MoMo API
        // 3. Verify callback signature
        // 4. Update transaction status
    }
}