# -*- coding: utf-8 -*-
"""
Day_6 参考解答
=============
主题：面向对象（三）—— descriptor 复刻 models.CharField（进阶）。
建议：先自己写，写不出来再看；看完后关掉文件自己默写一遍。
"""

_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


# 题目描述里想定义哪个类都可以（Article/Post 皆可），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_6 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"