import time
from typing import Any


class Cache:
    def __init__(self, ttl: int = 60):
        self._ttl = ttl
        self._store: dict[str, tuple[Any, float]] = {}

    def set(self, key: str, value: Any) -> None:
        self._store[key] = (value, time.time())

    def get(self, key: str) -> Any | None:
        if key not in self._store:
            return None
        value, ts = self._store[key]
        if time.time() - ts > self._ttl:
            return None
        return value

    def get_stale(self, key: str) -> Any | None:
        """Return cached value even if expired (stale-if-error fallback)."""
        if key not in self._store:
            return None
        return self._store[key][0]

    def invalidate(self, key: str) -> None:
        self._store.pop(key, None)