import dataclasses
import json
from dataclasses import dataclass


@dataclass(init=False)
class DataclassBase:
    def __init__(self, **kwargs):
        names = set([f.name for f in dataclasses.fields(self)])
        for k, v in kwargs.items():
            if k in names:
                setattr(self, k, v)


class Singleton(type):
    _instances = {}

    def __call__(cls, *args, **kwargs):
        if cls not in cls._instances:
            cls._instances[cls] = super(Singleton, cls).__call__(*args, **kwargs)
        return cls._instances[cls]


class DataclassJSONEncoder(json.JSONEncoder):
        def default(self, o):
            if dataclasses.is_dataclass(o):
                return dataclasses.asdict(o)
            return super().default(o)