[装饰器改进的策略模式]折扣改进#python

decorator_promotion.py

# 7 函数装饰器和闭包

## 使用装饰器改进策略模式

from collections import namedtuple

Customer = namedtuple('Customer', 'name fidelity')

class LineItem(object):
    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(object):  #上下文
    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(self)   # 调用策略得到打折值
        return self.total() - discount
    
    def __repr__(self):
        fmt = '<Order total:{:.2f} due:{:.2f}>'
        return fmt.format(self.total(), self.due())
    

promos = []
def promotion(promo_func):
    promos.append(promo_func)
    return promo_func


@promotion
def fidelity_promo(order):
    """积分1000->5%折扣"""
    return order.total() * .05 if order.customer.fidelity >= 1000 else 0


@promotion
def bulk_item_promo(order):
    """单个商品为20个或以上时提供10%折扣"""
    discount = 0
    for item in order.cart:
        if item.quantity >= 20:
            discount += item.total() * .1
    return discount


@promotion
def large_order_promo(order):
    """不同商品达到10个 7%折扣"""
    distinct_items = {item.product for item in order.cart}
    if len(distinct_items) >= 10:
        return order.total() * .07
    return 0


def best_promo(order):
    return max(promo(order) for promo in promos)


def test():
    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)]

    banana_cart = [LineItem('banana', 30, .5),
                   LineItem('apple', 10, 1.5)]

    long_order = [LineItem(str(item_code), 1, 1.0) 
                  for item_code in range(10)]


    print(Order(joe, banana_cart, best_promo))

test()