4) Сервисы (SRP + DIP)

4) Сервисы (SRP + DIP)

// SRP: каждый сервис делает своё; DIP: зависит от абстракций
public final class PricingService {
    private final DiscountPolicy discountPolicy;
    public PricingService(DiscountPolicy discountPolicy) { this.discountPolicy = discountPolicy; }
    public Money priceWithDiscount(Money total) { return discountPolicy.apply(total); }
}

public final class CheckoutService {
    private final Payment payment;
    private final Notifier notifier;
    private final OrderRepository repo;
    private final PricingService pricing;

    public CheckoutService(Payment payment, Notifier notifier, OrderRepository repo, PricingService pricing) {
        this.payment = payment;
        this.notifier = notifier;
        this.repo = repo;
        this.pricing = pricing;
    }

    public void checkout(Order order) {
        // 1) скидка
        Money discounted = pricing.priceWithDiscount(order.total());
        order.applyDiscount(discounted);

        // 2) оплата
        PaymentResult r = payment.pay(discounted);
        if (!r.success()) {
            notifier.send(order.customerEmail(), "Оплата не прошла: " + r.message());
            throw new IllegalStateException("Payment failed: " + r.message());
        }

        // 3) фиксация и уведомление
        order.markPaid();
        repo.save(order);
        notifier.send(order.customerEmail(), "Заказ " + order.id() + " оплачен (" + r.txId() + ")");
    }
}