from typing import TYPE_CHECKING

if TYPE_CHECKING:
    from .data_loader import DataLoader


class classproperty(property):
    def __get__(self, obj, objtype=None):
        return super(classproperty, self).__get__(objtype)

    def __set__(self, obj, value):
        super(classproperty, self).__set__(type(obj), value)

    def __delete__(self, obj):
        super(classproperty, self).__delete__(type(obj))


class DataloaderContext:
    _instance: 'DataloaderContext' = None

    def __init__(self) -> None:
        self.dataloader: 'DataLoader' = None

    @classproperty
    def instance(cls) -> 'DataloaderContext':
        if cls._instance is None:
            cls._instance = DataloaderContext()
        return cls._instance