# -*- coding: utf-8 -*-
"""
Day_3 参考解答
=============
用纯 Python 复刻 Django Model 的机制。
建议：先自己写，写不出来再看；看完后关掉文件自己默写。
"""

import time

# ============================================================
# 题目一：设计一个 User 类
# ============================================================

class User:
    all_users = []          # 类属性：模拟数据库表

    def __init__(self, name, email, age):
        self.name = name
        self.email = email
        self.age = age
        User.all_users.append(self)          # 把新用户"存表"

    def get_full_name(self):
        return f"用户：{self.name}（{self.email}）"

    def __str__(self):
        # 给"人"看的：print(user) 时显示，Django admin 列表里显示的就是它
        return self.name

    def __repr__(self):
        # 给"开发者调试"看的：要能还原出原对象，eval(repr(u)) 应得到相同信息
        return f"User(name={self.name!r}, email={self.email!r}, age={self.age!r})"


if __name__ == '__main__':
    u1 = User("zhangsan", "zs@163.com", 20)
    u2 = User("lisi", "ls@163.com", 21)
    u3 = User("wangwu", "ww@163.com", 19)

    for u in User.all_users:
        print(u, "->", repr(u))
    # zhangsan -> User(name='zhangsan', email='zs@163.com', age=20)
    # lisi -> User(name='lisi', email='ls@163.com', age=21)
    # wangwu -> User(name='wangwu', email='ww@163.com', age=19)

    restored = eval(repr(u1))                # __repr__ 的用途：可还原
    print(restored.name, restored.email)     # zhangsan zs@163.com

    # 思考题答案：
    # __str__ 面向普通用户/展示，__repr__ 面向开发者/调试，且要求无歧义可还原；
    # 只实现 __repr__ 时，print() 会退而使用 __repr__；反之不会。


# ============================================================
# 题目二：继承 —— 复刻 models.Model
# ============================================================

class BaseModel:
    objects = []            # 类属性：模拟数据库表（所有子类共用）

    def save(self):
        BaseModel.objects.append(self)
        print(f"[DB] 已保存 {type(self).__name__}: {self}")

    def delete(self):
        BaseModel.objects.remove(self)
        print(f"[DB] 已删除 {self}")

    def to_dict(self):
        return dict(self.__dict__)           # 实例的所有属性 => 字典

    def __str__(self):
        return f"<{type(self).__name__}#{id(self)}>"


class Article(BaseModel):
    def __init__(self, title, content, author):
        self.title = title
        self.content = content
        self.author = author
        self.created_at = time.strftime("%Y-%m-%d %H:%M:%S")

    # 进阶：重写 save，先打日志，再调用父类逻辑
    def save(self):
        print(f"[LOG] 正在保存文章《{self.title}》...")
        super().save()                       # 父类的 save 负责真正"入库"

    def __str__(self):
        return f"<Article: {self.title}>"


class Comment(BaseModel):
    def __init__(self, content, author):
        self.content = content
        self.author = author

    def __str__(self):
        return f"<Comment: {self.content[:10]}...>"


if __name__ == '__main__':
    a1 = Article("Django 入门", "从 Hello World 开始", "zhangsan")
    a1.save()                                # 触发重写后的 save（带日志 + super）
    c1 = Comment("写得太好了！", "lisi")
    c1.save()

    for obj in BaseModel.objects:
        print(obj.to_dict())

    print(issubclass(Article, BaseModel))    # True
    print(isinstance(a1, BaseModel))         # True

    a1.delete()
    print(len(BaseModel.objects))            # 1（只剩评论）


# ============================================================
# 题目三（进阶）：descriptor —— 复刻 models.CharField
# ============================================================

_NOT_SET = object()          # 哨兵值：表示"字段还没赋过值"


class CharField:
    def __init__(self, max_length=255):
        self.max_length = max_length
        self.name: str | None = None  # 字段对应的属性名，由 ModelBase.__init_subclass__ 填入

    def __get__(self, instance, owner):
        if instance is None:
            return self      # 通过类访问（Article.title）：返回描述符本身
        return instance.__dict__.get(self.name, _NOT_SET)

    def __set__(self, instance, value):
        if not isinstance(value, str):
            raise ValueError(f"{self.name} 必须是字符串")
        if len(value) > self.max_length:
            raise ValueError(f"{self.name} 长度不能超过 {self.max_length}")
        instance.__dict__[self.name] = value   # 存到实例自己的字典里


class EmailField(CharField):
    def __set__(self, instance, value):
        if "@" not in value or "." not in value:
            raise ValueError(f"{self.name} 不是合法的邮箱格式")
        super().__set__(instance, value)       # 通过校验后再走父类存储


class IntegerField:
    def __init__(self, min_value=None, max_value=None):
        self.min_value = min_value
        self.max_value = max_value
        self.name: str | None = None

    def __get__(self, instance, owner):
        if instance is None:
            return self
        return instance.__dict__.get(self.name, _NOT_SET)

    def __set__(self, instance, value):
        # bool 是 int 的子类，所以要显式排除 True/False
        if not isinstance(value, int) or isinstance(value, bool):
            raise ValueError(f"{self.name} 必须是整数")
        if self.min_value is not None and value < self.min_value:
            raise ValueError(f"{self.name} 不能小于 {self.min_value}")
        if self.max_value is not None and value > self.max_value:
            raise ValueError(f"{self.name} 不能大于 {self.max_value}")
        instance.__dict__[self.name] = value


class ModelBase:
    # 子类定义完成后自动调用：把每个 Field 对象和它的属性名绑定
    def __init_subclass__(cls, **kwargs):
        super().__init_subclass__(**kwargs)
        for attr_name, attr_value in cls.__dict__.items():
            if isinstance(attr_value, (CharField, IntegerField)):
                attr_value.name = attr_name


# 为避免与本文件上方题目二的 Article 类重名，这里命名为 Post，
# 题目描述里想定义哪个类都可以，机制完全相同。
class Post(ModelBase):
    title = CharField(max_length=50)
    content = CharField(max_length=1000)
    author_email = EmailField(max_length=100)
    views = IntegerField(min_value=0)


if __name__ == '__main__':
    a = Post()
    a.title = "Django 入门"
    a.content = "跟着 Day_3 慢慢理解框架"
    a.author_email = "zs@163.com"
    a.views = 10
    print(a.title, a.views, a.author_email)    # Django 入门 10 zs@163.com
    print(Post.title)                          # 类访问 => CharField 对象本身

    # 以下三条都应该抛 ValueError，逐行取消注释验证
    # a.title = "x" * 100
    # a.views = -5
    # a.author_email = "not-an-email"

    # 尚未赋值的字段返回哨兵（不是属性不存在，也不是默认值）
    print(a.__dict__.get("views"))             # 已被赋值为 10