from __future__ import annotations

import json
import os
import tempfile
from typing import Any, Optional, Tuple


def cache_dir() -> str:
    """Directory where the scheduler owner writes shared cache JSON files."""
    d = os.environ.get("LAIR_CACHE_DIR", "/tmp/lair-cache")
    os.makedirs(d, exist_ok=True)
    return d


def cache_file(name: str) -> str:
    return os.path.join(cache_dir(), f"{name}.json")


def atomic_write_json(path: str, payload: dict) -> None:
    """Write JSON atomically so readers never observe partial content."""
    parent = os.path.dirname(path) or "."
    fd, tmp = tempfile.mkstemp(prefix=".tmp-", dir=parent)
    try:
        with os.fdopen(fd, "w", encoding="utf-8") as f:
            json.dump(payload, f, ensure_ascii=False, separators=(",", ":"))
        os.replace(tmp, path)
    finally:
        try:
            if os.path.exists(tmp):
                os.unlink(tmp)
        except Exception:
            pass


def load_json_if_newer(path: str, last_mtime: float) -> Tuple[Optional[dict], float]:
    """Load JSON only if the file exists and has mtime newer than last_mtime."""
    try:
        st = os.stat(path)
    except FileNotFoundError:
        return None, last_mtime
    except Exception:
        return None, last_mtime

    mtime = float(st.st_mtime)
    if mtime <= float(last_mtime):
        return None, last_mtime

    try:
        with open(path, "r", encoding="utf-8") as f:
            return json.load(f), mtime
    except Exception:
        return None, last_mtime