## Service Layer Pattern

```python
# apps/orders/services.py
from typing import Optional
from django.db import transaction
from .models import Order, OrderItem

class OrderService:
    """Service layer for order-related business logic."""

    @staticmethod
    @transaction.atomic
    def create_order(user, cart: Cart) -> Order:
        """Create order from cart."""
        order = Order.objects.create(
            user=user,
            total_price=cart.total_price
        )

        for item in cart.items.all():
            OrderItem.objects.create(
                order=order,
                product=item.product,
                quantity=item.quantity,
                price=item.product.price
            )

        # Clear cart
        cart.items.all().delete()

        return order

    @staticmethod
    def process_payment(order: Order, payment_data: dict) -> bool:
        """Process payment for order."""
        # Integration with payment gateway
        payment = PaymentGateway.charge(
            amount=order.total_price,
            token=payment_data['token']
        )

        if payment.success:
            order.status = Order.Status.PAID
            order.save()
            # Send confirmation email
            OrderService.send_confirmation_email(order)
            return True

        return False

    @staticmethod
    def send_confirmation_email(order: Order):
        """Send order confirmation email."""
        # Email sending logic
        pass
```