Open-Closed Princple - PayementGateway TypeScript Example

interface Order {
    order_id: string;
}

// ✅ Good
// Extending the payment service without modifying existing code (Open-Closed Principle)
abstract class PaymentGateway {
    abstract processPayment(order: Order): void;
}

class CreditCardGateway extends PaymentGateway {
    processPayment(order: Order): void {
        console.log("// Process credit card payment for order: " + order.order_id);
    }
}

class PayPalGateway extends PaymentGateway {
    processPayment(order: Order): void {
        console.log("// Process PayPal payment for order: " + order.order_id);
    }
}

class BitcoinGateway extends PaymentGateway {
    processPayment(order: Order): void {
        console.log("// Process Bitcoin payment for order: " + order.order_id);
    }
}

// Maybe you want to add support for a new payment Method 🤔 👇
class ApplePayGateway extends PaymentGateway {
    processPayment(order: Order): void {
        console.log("// Process ApplePay payment for order: " + order.order_id);
    }
}

enum PAYMENT_METHOD {
    CREDIT_CARD = 'credit-card',
    PAYPAL = 'paypal',
    BITCOIN = 'bitcoin',
    APPLE_PAY = 'apple-pay', // Added ApplePay to the enum
}

class PaymentService {
    private paymentGateways: Record<string, PaymentGateway> = {};

    public registerPaymentGateway(paymentMethod: PAYMENT_METHOD, gateway: PaymentGateway) {
        this.paymentGateways[paymentMethod] = gateway;
    }

    public async processPayment(order: Order, paymentMethod: PAYMENT_METHOD) {
        const gateway = this.paymentGateways[paymentMethod];
        if (gateway) {
            await gateway.processPayment(order);
        } else {
            throw new Error('Unsupported payment method!');
        }
    }
}

// Create an order
const order: Order = { order_id: "12345" };

// Initialize the payment service
const newPayment = new PaymentService();

// Register payment gateways
newPayment.registerPaymentGateway(PAYMENT_METHOD.CREDIT_CARD, new CreditCardGateway());
newPayment.registerPaymentGateway(PAYMENT_METHOD.PAYPAL, new PayPalGateway());
newPayment.registerPaymentGateway(PAYMENT_METHOD.BITCOIN, new BitcoinGateway());
newPayment.registerPaymentGateway(PAYMENT_METHOD.APPLE_PAY, new ApplePayGateway()); // Registering ApplePay

// Process a payment
newPayment.processPayment(order, PAYMENT_METHOD.PAYPAL);