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'''
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职责链模式（Chain of Responsibility Pattern）
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一种行为设计模式，它允许你将请求沿着处理者链进行发送。
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收到请求后，每个处理者均可对请求进行处理，或将其传递给链上的下个处理者。
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在书城的业务背景中，可以想象有这样的场景：
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客户下了一个订单，该订单需要经历多个处理步骤，比如验证库存、计算价格、生成发货通知等。
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这些处理步骤按照一定的顺序组织成一个处理链
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'''
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class Order:
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def __init__(self, book_id, quantity):
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self.book_id = book_id
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self.quantity = quantity
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class Handler:
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def __init__(self, successor=None):
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self.successor = successor
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def handle_request(self, order):
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raise NotImplementedError("Subclasses must implement handle_request()")
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def successor_handle_request(self, order):
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if self.successor is not None:
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return self.successor.handle_request(order)
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class InventoryHandler(Handler):
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def handle_request(self, order):
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if check_inventory(order.book_id, order.quantity):
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print("InventoryHandler: Inventory checked, enough stock.")
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return self.successor_handle_request(order)
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else:
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print("InventoryHandler: Inventory check failed, not enough stock.")
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return False
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class PricingHandler(Handler):
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def handle_request(self, order):
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price = calculate_price(order.book_id, order.quantity)
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print(f"PricingHandler: Price calculated, total: {price}")
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return self.successor_handle_request(order)
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class NotificationHandler(Handler):
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def handle_request(self, order):
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send_notification(order)
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print("NotificationHandler: Notification sent to customer.")
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# Since this is the end of the chain, no successor to call.
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return True
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# Dummy functions to simulate the bookstore logic
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def check_inventory(book_id, quantity):
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return True # Simulate enough stock
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def calculate_price(book_id, quantity):
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return 10.0 * quantity # Simulate a fixed price per book
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def send_notification(order):
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pass # Simulate sending a notification to the customer
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# Setting up the Chain of Responsibility
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inventory_handler = InventoryHandler()
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pricing_handler = PricingHandler()
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notification_handler = NotificationHandler()
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inventory_handler.successor = pricing_handler
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pricing_handler.successor = notification_handler
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# Client code
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order = Order(book_id="12345", quantity=2)
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result = inventory_handler.handle_request(order)
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if result:
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print("Order processing completed successfully.")
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else:
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print("Order processing failed.")
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'''
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在这个例子中，我们有一个Handler基类，它定义了一个处理请求的基本框架。
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具体的处理逻辑则在子类InventoryHandler、PricingHandler和NotificationHandler中实现。
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这些子类形成了职责链，通过successor引用链接在一起。
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客户下了一个订单后，这个订单请求会从库存处理器（InventoryHandler）开始处理。
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如果库存足够，请求将被传递给价格处理器（PricingHandler）来计算总价。
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然后，价格处理器再将请求传递给通知处理器（NotificationHandler），
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最后发送通知给客户。
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如果任何处理器无法处理请求（例如，库存不足），处理将在那里终止，并且返回相应的结果。
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这个模式的好处是可以很容易地改变处理的顺序或者增加/删除处理器，而不需要修改已有的代码。
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'''
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