import json
import os
import tempfile
import time
from dataclasses import dataclass
from pathlib import Path
from typing import Any


@dataclass
class CacheEntry:
    value: Any
    stale: bool


class FileCache:
    def __init__(self, cache_dir: str, default_ttl_seconds: int) -> None:
        self.cache_dir = Path(cache_dir)
        self.cache_dir.mkdir(parents=True, exist_ok=True)
        self.default_ttl_seconds = default_ttl_seconds

    def _path_for(self, key: str) -> Path:
        safe_key = "".join(c if c.isalnum() or c in ("-", "_") else "_" for c in key)
        return self.cache_dir / f"{safe_key}.json"

    def _read_raw(self, key: str) -> dict[str, Any] | None:
        path = self._path_for(key)
        if not path.exists():
            return None
        try:
            return json.loads(path.read_text(encoding="utf-8"))
        except (OSError, json.JSONDecodeError):
            return None

    def get_json(self, key: str, allow_stale: bool = False) -> CacheEntry | None:
        payload = self._read_raw(key)
        if payload is None:
            return None

        expires_at = float(payload.get("expires_at", 0))
        value = payload.get("value")
        stale = time.time() > expires_at
        if stale and not allow_stale:
            return None
        return CacheEntry(value=value, stale=stale)

    def set_json(self, key: str, value: Any, ttl_seconds: int | None = None) -> None:
        ttl = ttl_seconds if ttl_seconds is not None else self.default_ttl_seconds
        payload = {
            "expires_at": time.time() + max(ttl, 0),
            "value": value,
        }
        self._atomic_write_json(self._path_for(key), payload)

    def _atomic_write_json(self, path: Path, payload: dict[str, Any]) -> None:
        fd, tmp_name = tempfile.mkstemp(prefix="cache_", suffix=".tmp", dir=str(self.cache_dir))
        try:
            with os.fdopen(fd, "w", encoding="utf-8") as tmp_file:
                json.dump(payload, tmp_file, separators=(",", ":"))
            os.replace(tmp_name, path)
        finally:
            if os.path.exists(tmp_name):
                os.remove(tmp_name)