lectures/design_pattern/lec3_design_principle.py

from abc import ABC, abstractmethod
from typing import List, Protocol

"""
Lec 3: 设计原则 (Design Principles)
这些代码示例展示了 SOLID 原则及其他核心设计原则在 Python 中的实现。
"""

# -----------------------------------------------------------------------------
# 1. 单一职责原则 (Single Responsibility Principle, SRP)
# -----------------------------------------------------------------------------

class Report:
    """负责数据逻辑的类"""
    def __init__(self, data: List[float]):
        self.data = data

    def calculate_summary(self) -> float:
        return sum(self.data) / len(self.data) if self.data else 0.0

class PDFExporter:
    """负责 PDF 导出的类"""
    def export(self, report: Report, filepath: str):
        summary = report.calculate_summary()
        print(f"[PDF] 导出摘要: {summary} 到文件: {filepath}")

class HTMLExporter:
    """负责 HTML 导出的类"""
    def export(self, report: Report, filepath: str):
        summary = report.calculate_summary()
        print(f"[HTML] 导出摘要: {summary} 到文件: {filepath}")


# -----------------------------------------------------------------------------
# 2. 开放-封闭原则 (Open-Closed Principle, OCP)
# -----------------------------------------------------------------------------

class Shape(ABC):
    @abstractmethod
    def area(self) -> float:
        pass

class Rectangle(Shape):
    def __init__(self, width: float, height: float):
        self.width = width
        self.height = height

    def area(self) -> float:
        return self.width * self.height

class Circle(Shape):
    def __init__(self, radius: float):
        self.radius = radius

    def area(self) -> float:
        import math
        return math.pi * (self.radius ** 2)

def print_areas(shapes: List[Shape]):
    """对扩展开放：可以添加新形状而无需修改此函数"""
    for shape in shapes:
        print(f"Shape area: {shape.area()}")


# -----------------------------------------------------------------------------
# 3. 里氏替换原则 (Liskov Substitution Principle, LSP)
# -----------------------------------------------------------------------------

class Bird(ABC):
    pass

class FlyingBird(Bird):
    @abstractmethod
    def fly(self):
        pass

class NonFlyingBird(Bird):
    pass

class Sparrow(FlyingBird):
    def fly(self):
        print("麻雀正在飞翔...")

class Ostrich(NonFlyingBird):
    def run(self):
        print("鸵鸟正在奔跑...")


# -----------------------------------------------------------------------------
# 4. 依赖倒置原则 (Dependency Inversion Principle, DIP)
# -----------------------------------------------------------------------------

class MessageSender(ABC):
    @abstractmethod
    def send(self, message: str):
        pass

class EmailSender(MessageSender):
    def send(self, message: str):
        print(f"发送邮件通知: {message}")

class SMSSender(MessageSender):
    def send(self, message: str):
        print(f"发送短信通知: {message}")

class NotificationService:
    def __init__(self, sender: MessageSender):
        # 依赖于抽象接口 MessageSender，而不是具体的 EmailSender 或 SMSSender
        self.sender = sender

    def notify(self, message: str):
        self.sender.send(message)


# -----------------------------------------------------------------------------
# 5. 接口隔离原则 (Interface Segregation Principle, ISP)
# -----------------------------------------------------------------------------

class Workable(Protocol):
    def work(self) -> None: ...

class Eatable(Protocol):
    def eat(self) -> None: ...

class Human(Workable, Eatable):
    def work(self) -> None:
        print("人类在工作...")

    def eat(self) -> None:
        print("人类在吃饭...")

class Robot(Workable):
    def work(self) -> None:
        print("机器人在工作...")


# -----------------------------------------------------------------------------
# 6. 合成/聚合复用原则 (Composite/Aggregate Reuse Principle, CARP)
# -----------------------------------------------------------------------------

class Engine:
    def start(self):
        print("发动机已启动")

class Car:
    def __init__(self, engine: Engine):
        # 使用组合而非继承
        self.engine = engine

    def start(self):
        print("汽车准备出发...")
        self.engine.start()


# -----------------------------------------------------------------------------
# 7. 迪米特法则 (Law of Demeter, LoD)
# -----------------------------------------------------------------------------

class Teacher:
    def command(self, group_leader):
        # 老师只下令给组长，不直接接触学生
        group_leader.count_students()

class GroupLeader:
    def __init__(self, students):
        self.students = students

    def count_students(self):
        print(f"学生总人数: {len(self.students)}")


# -----------------------------------------------------------------------------
# 演示运行
# -----------------------------------------------------------------------------

if __name__ == "__main__":
    print("--- SRP ---")
    my_report = Report([10.5, 20.0, 15.5])
    pdf_exp = PDFExporter()
    pdf_exp.export(my_report, "data.pdf")

    print("\n--- OCP ---")
    shapes = [Rectangle(10, 5), Circle(7)]
    print_areas(shapes)

    print("\n--- LSP ---")
    sparrow = Sparrow()
    sparrow.fly()

    print("\n--- DIP ---")
    service = NotificationService(SMSSender())
    service.notify("您有一条新消息")

    print("\n--- ISP ---")
    worker = Robot()
    worker.work()

    print("\n--- CARP ---")
    engine = Engine()
    my_car = Car(engine)
    my_car.start()

    print("\n--- LoD ---")
    students = ["Alice", "Bob", "Charlie"]
    leader = GroupLeader(students)
    teacher = Teacher()
    teacher.command(leader)