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'''
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建造者模式（Builder Pattern）允许构建一个复杂对象的各个部分，然后一步一步地返回这个对象的完整版本。
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将建造者模式应用于网购的下单和出库过程时，我们可以设计一个Order类来表示订单，
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以及一个OrderBuilder类来构建订单的各个部分。
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此外，我们还可以引入一个ShoppingCart类来表示购物车，以及一个Inventory类来处理库存和出库逻辑。
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'''
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######################################################################
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# Order类，它包含订单的基本信息，如下单时间、用户信息、订单项列表
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######################################################################
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from datetime import datetime
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class OrderItem:
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def __init__(self, product_id, quantity):
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self.product_id = product_id
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self.quantity = quantity
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class Order:
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def __init__(self, user_id, order_items, order_time=None):
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self.user_id = user_id
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self.order_items = order_items
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self.order_time = order_time or datetime.now()
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self.status = "PLACED" # 初始状态为已下单
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def __str__(self):
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return f"Order for user {self.user_id} placed at {self.order_time}. Status: {self.status}"
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def fulfill(self, inventory):
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# 出库逻辑，这里简化处理
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for item in self.order_items:
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if not inventory.deduct_stock(item.product_id, item.quantity):
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return False
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self.status = "FULFILLED"
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return True
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######################################################################
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# OrderBuilder类，用于构建订单
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######################################################################
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class OrderBuilder:
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def __init__(self):
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self.reset()
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def reset(self):
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self._user_id = None
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self._order_items = []
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def for_user(self, user_id):
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self._user_id = user_id
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return self
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def add_item(self, product_id, quantity):
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self._order_items.append(OrderItem(product_id, quantity))
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return self
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def build(self):
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if not self._user_id or not self._order_items:
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raise ValueError("Order cannot be built without user and items.")
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return Order(self._user_id, self._order_items)
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######################################################################
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# 购物车和库存类
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######################################################################
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class ShoppingCart:
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def __init__(self, user_id):
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self.user_id = user_id
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self.items = {} # {product_id: quantity}
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def add_to_cart(self, product_id, quantity):
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self.items[product_id] = self.items.get(product_id, 0) + quantity
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def checkout(self):
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order_items = [OrderItem(product_id, quantity) for product_id, quantity in self.items.items()]
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self.items.clear() # 清空购物车
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return order_items
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class Inventory:
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def __init__(self):
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self.stock = {} # {product_id: quantity}
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def add_stock(self, product_id, quantity):
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self.stock[product_id] = self.stock.get(product_id, 0) + quantity
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def deduct_stock(self, product_id, quantity):
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if self.stock.get(product_id, 0) >= quantity:
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self.stock[product_id] -= quantity
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return True
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return False
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######################################################################
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# 模拟整个下单和出库过程
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######################################################################
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# 初始化库存和购物车
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inventory = Inventory()
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inventory.add_stock("book1", 10)
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inventory.add_stock("book2", 5)
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cart = ShoppingCart(user_id="user123")
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cart.add_to_cart("book1", 2)
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cart.add_to_cart("book2", 1)
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# 使用OrderBuilder构建订单
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order_items = cart.checkout() # 结账，获取订单项列表并清空购物车
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order_builder = OrderBuilder().for_user("user123")
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for item in order_items:
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order_builder.add_item(item.product_id, item.quantity)
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order = order_builder.build() # 构建订单对象
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print(order) # 输出订单信息
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# 出库处理
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if order.fulfill(inventory):
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print("Order has been fulfilled.")
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else:
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print("Order fulfillment failed due to insufficient stock.") |
