import json
from typing import Dict
from dataclasses import (
    asdict, dataclass, field, fields, is_dataclass
)


# 对于一些嵌套的数据类，需要深度遍历
class EnhancedJSONEncoder(json.JSONEncoder):
    def default(self, o):
        if is_dataclass(o):
            return asdict(o)
        return super().default(o)


def dicts_to_dataclasses(instance):
    """将所有的数据类属性都转化到数据类中"""
    cls = type(instance)
    for f in fields(cls):
        if not is_dataclass(f.type):
            continue

        value = getattr(instance, f.name)
        if not isinstance(value, dict):
            continue

        new_value = f.type(**value)
        setattr(instance, f.name, new_value)


@dataclass
class Base:
    def __post_init__(self):
        dicts_to_dataclasses(self)

    def as_dict(self):
        return asdict(self)

    def as_json(self):
        return json.dumps(self, cls=EnhancedJSONEncoder)

if __name__ == "__main__":
    @dataclass
    class Download(Base):
        url: str
        expire_time: int
        headers: Dict = field(default_factory=dict)
     
        download = {
        'url': 'http://example.com',
        'expire_time': 1,
        'headers': {
            'Content-Type': 'application/json'
        }
    }
    
    d = Download(**download)
    print(d.as_dict())
    print(d.as_json())