from abc import ABC,abstractmethod
from collections import namedtuple
#给每个顾客的属性起个名字，作为整体传入process后，调用时不必用customer[0]这样的方式索引，
#可以直接customer.name，方便阅读与查错。
Customer = namedtuple('Customer','name fidelity')

class LineItem:
    def __init__(self,product,quantity,price):
        self.product  = product
        self.quantity = quantity
        self.price    = price
    def total(self):
        return self.price * self.quantity

class Order :
    def __init__(self,customer,cart,promotion=None):
        self.customer   = customer
        self.cart       = list(cart)
        self.promotion  = promotion

    def total(self):
        if not hasattr(self, '__total'):
            self.__total = sum(item.total() for item in self.cart)
        return self.__total

    def due(self):
        if self.promotion is None:
            discount = 0
        else:
            discount = self.promotion.discount(self)
        return self.total() - discount

    def __repr__(self):
        fmt = '<Order total: {:.2f} due: {:.2f}>'
        return fmt.format(self.total(), self.due())

"""class Promotion(ABC):

    @abstractmethod
    def discount(self,order):
        Return discount as a positive dollar amount"""

class FidelityPromo():
    """5% discount for customers with 1000 or more fidelity points"""

    def discount(self,order):
        return order.total() * .05 if order.customer.fidelity >= 1000 else 0

class BulkItemPromo(): #second Concrete Strategy
    """10% discount for each LineItem with 20 or more units"""

    def discount(self,order):
        discount = 0
        for item in order.cart:
            if item.quantity >= 20:
                discount += item.total() * .1
        return discount


class LargeOrderProme(): #third Concrete Strategy
    """7% discount for orders with 10 or more distinct items"""

    def discount(self, order):
        distinct_items = {item.product for item in order.cart}
        if len(distinct_items)>=10:
            return order.total() * .07
        return 0

joe = Customer('John Doe', 0)
ann = Customer('Ann Smith', 1100)
cart = [LineItem('banana', 4, .5),LineItem('apple', 10, 1.5),LineItem('watermellon', 5, 5.0)]
a=Order(joe, cart, FidelityPromo())
print(a)
print(Order(ann, cart, FidelityPromo()))




