from typing import Callable, Generic, TypeVar

T = TypeVar("T")


class SingletonProvider(Generic[T]):
    def __init__(self, factory: Callable[[], T]):
        self._factory = factory
        self._instance: T | None = None

    def __call__(self) -> T:
        if self._instance is None:
            self._instance = self._factory()
        return self._instance

    def reset(self) -> None:
        """重置单例（测试 / 热重载用）"""
        self._instance = None

    def warmup(self) -> T:
        """提前初始化"""
        return self()