第三天：创建型模式--建造者模式

零、建造者模式

• 什么是建造者模式
  使用多个简单的对象一步一步构建成一个复杂的对象。这种类型的设计模式属于建造者模式，它提供了一种创建对象的最佳方式，将一个复杂对象的构造过程与其表象分离，同一个构造过程可用于创建多个不同的表现。

一、身边的例子

• 麦当劳
  麦当劳的汉堡套餐种类有很多（如：汉堡+可乐、汉堡+薯条、汉堡+可乐+薯条），顾客在购买的时候关注的是套餐的种类（表现），而不关注套餐制作的过程（建造过程）。在这里顾客就是客户端，收银员就是指挥者，后厨人员就是建造者。
• django-widgy
  django-widgy是Django的第三方编辑器扩展，可以构建不同风格的HTML代码。

二、什么情况下使用

创建一个由多个部分构成的对象，而且它的构成需要一步接一步地完成，只有当各个部分都创建好后，这个对象才算创建完成。

三、应用案例

以下代码，通过订购两种不同口味的比萨并，来进一步学习建造者模式

import time
from enum import Enum

PizzaProgress = Enum('PizzaProgress', 'queued preparation baking ready')
PizzaDough = Enum('PizzaDough', 'thin thick')
PizzaSauce = Enum('PizzaSauce', 'tomato creme_fraiche')
PizzaTopping = Enum('PizzaTopping', 'mozzarella double_mozzarella bacon ham mushrooms red_onion oregano')
STEP_DELAY = 3


class Pizza:
    '''
    最终产品类
    '''

    def __init__(self, name):
        self.name = name
        self.dough = None
        self.sauce = None
        self.topping = []

    def __str__(self):
        return self.name

    def prepare_dough(self, dough):
        self.dough = dough
        print('preparing the {} dough of you {}...'.format(self.dough.name, self))
        time.sleep(STEP_DELAY)
        print('done with the {} dough'.format(self.dough.name))


class CreamyBaconBuilder:
    """
    奶油熏肉比萨建造者
    """

    def __init__(self):
        self.pizza = Pizza('creamy bacon')
        self.progress = PizzaProgress.queued
        # 烤制时间
        self.baking_time = 7

    # 生面团
    def prepare_dough(self):
        self.progress = PizzaProgress.preparation
        self.pizza.prepare_dough(PizzaDough.thin)

    # 添加沙司
    def add_sauce(self):
        print('adding the creme fraiche sauce to your creamy bacon')
        self.pizza.sauce = PizzaSauce.Creme_fraiche
        # 暂停3秒，模拟制作的时间
        time.sleep(STEP_DELAY)
        print('done with the creme fraiche sauce')

    # 添加各种配料
    def add_topping(self):
        print('adding the topping (mozzarella,bacon,ham,mushrooms,red onion,oregano) to your creamy bacon')
        self.pizza.topping.append([t for t in (
            PizzaTopping.mozzarella, PizzaTopping.bacon, PizzaTopping.ham, PizzaTopping.mushrooms,
            PizzaTopping.red_onion, PizzaTopping.oregano)])
        time.sleep(STEP_DELAY)
        print('done with the topping (mozzarella,bacon,ham,mushrooms,red onion, oregano)')

    # 烤比萨
    def bake(self):
        self.progress = PizzaProgress.baking
        print('baking your creamy bacon for {} seconds'.format(self.baking_time))
        time.sleep(self.baking_time)
        self.progress = PizzaProgress.ready
        print('your creamy bacon is ready')


class MargaritaBuilder:
    '''
    玛格丽特比萨建造者
    '''

    def __init__(self):
        self.pizza = Pizza('margarita')
        self.progress = PizzaProgress.queued
        self.baking_time = 5

    def prepare_dough(self):
        self.progress = PizzaProgress.preparation
        self.pizza.prepare_dough(PizzaDough.thin)

    def add_sauce(self):
        print('adding the tomato sauce to your margarita...')
        self.pizza.sauce = PizzaSauce.tomato
        time.sleep(STEP_DELAY)
        print('done with the tomato sauce')

    def add_topping(self):
        print('adding the topping (double mozzarella, oregano) to your margarita')
        self.pizza.topping.append([i for i in (PizzaTopping.double_mozzarella, PizzaTopping.oregano)])
        time.sleep(STEP_DELAY)
        print('done with the topping (double mozzarrella,oregano)')

    def bake(self):
        self.progress = PizzaProgress.baking
        print('baking your margarita for {} seconds'.format(self.baking_time))
        time.sleep(self.baking_time)
        self.progress = PizzaProgress.ready
        print('your margarita is ready')


class Waiter:
    '''
    服务员（指挥者）
    '''

    def __init__(self):
        self.builder = None

    def construct_pizza(self, builder):
        self.builder = builder
        [step() for step in (builder.prepare_dough, builder.add_sauce, builder.add_topping, builder.bake)]

    @property
    def pizza(self):
        return self.builder.pizza


def validate_style(builders):
    '''
    验证输入类
    '''
    try:
        pizza_style = input('What pizza would you like ,[m]argarita or [c]reamy bacon?')
        builder = builders[pizza_style]()
        vaild_input = True
    except KeyError as err:
        print('Sorry,only margarita (key m) and creamy bacon (key c) are availabke')
        return (False, None)
    return (True, builder)


def main():
    builders = dict(m=MargaritaBuilder, c=CreamyBaconBuilder)
    valid_input = False
    while not valid_input:
        valid_input, builder = validate_style(builders)
    waiter = Waiter()
    waiter.construct_pizza(builder)
    pizza = waiter.pizza
    print('Enjoy your  {}!'.format(pizza))


if __name__ == '__main__':
    main()