Strategy Pattern

// Strategy Interface
class PaymentStrategy {
  pay(amount) { throw "Must implement!"; }
}

// Concrete Strategies
class CashPayment extends PaymentStrategy {
  pay(amount) { return `💵 Paid ${amount} EGP in cash`; }
}

class VisaPayment extends PaymentStrategy {
  pay(amount) { return `💳 Paid ${amount} EGP via Visa - 2% fee applied`; }
}

class InstapayPayment extends PaymentStrategy {
  pay(amount) { return `📱 Paid ${amount} EGP via Instapay - instant!`; }
}

// Context
class ShoppingCart {
  constructor() { this.total = 0; }
  
  setPaymentStrategy(strategy) {
    this.paymentStrategy = strategy; // غيّر الـ Strategy!
  }
  
  checkout() {
    return this.paymentStrategy.pay(this.total);
  }
}

// Usage - سهل تغيير الـ Strategy!
const cart = new ShoppingCart();
cart.total = 500;

cart.setPaymentStrategy(new CashPayment());
cart.checkout(); // 💵 Paid 500 EGP in cash

cart.setPaymentStrategy(new VisaPayment());
cart.checkout(); // 💳 Paid 500 EGP via Visa