Facade Example: Placing an Order Across Stock, Payment and Shipping

class Inventory:
    def __init__(self, stock: dict[str, int]) -> None:
        self._stock = stock

    def reserve(self, sku: str, quantity: int) -> bool:
        if self._stock.get(sku, 0) < quantity:
            return False
        self._stock[sku] -= quantity
        print(f"inventory: reserved {quantity} x {sku}")
        return True

    def release(self, sku: str, quantity: int) -> None:
        self._stock[sku] += quantity
        print(f"inventory: released {quantity} x {sku}")


class PaymentService:
    def charge(self, card: str, pence: int) -> bool:
        approved = not card.endswith("0000")
        print(f"payment: {pence} pence on card ending {card[-4:]}, {'approved' if approved else 'declined'}")
        return approved


class Shipping:
    def book(self, sku: str, address: str) -> str:
        print(f"shipping: courier booked for {sku} to {address}")
        return "SHIP-7781"


class OrderFacade:
    def __init__(self, inventory: Inventory, payments: PaymentService, shipping: Shipping) -> None:
        self._inventory = inventory
        self._payments = payments
        self._shipping = shipping

    def place_order(self, sku: str, quantity: int, card: str, pence: int, address: str) -> str:
        if not self._inventory.reserve(sku, quantity):
            return "out of stock"
        if not self._payments.charge(card, pence):
            self._inventory.release(sku, quantity)
            return "payment declined"
        return self._shipping.book(sku, address)


shop = OrderFacade(Inventory({"LAMP-01": 3}), PaymentService(), Shipping())
print(shop.place_order("LAMP-01", 1, "4111111111111111", 3999, "Leeds"))
print(shop.place_order("LAMP-01", 1, "4000000000000000", 3999, "York"))