# -*- coding: utf-8 -*-
from __future__ import annotations
import json, os, shutil, tempfile
from datetime import datetime, timezone
from pathlib import Path
from typing import Any


def utc_now() -> str:
    return datetime.now(timezone.utc).isoformat(timespec="seconds")


def atomic_json_write(path: str | Path, payload: Any, backup_dir: str | Path | None = None) -> None:
    target = Path(path)
    target.parent.mkdir(parents=True, exist_ok=True)
    if backup_dir and target.exists():
        bdir = Path(backup_dir); bdir.mkdir(parents=True, exist_ok=True)
        stamp = datetime.now(timezone.utc).strftime("%Y%m%dT%H%M%S%fZ")
        shutil.copy2(target, bdir / f"{target.stem}_{stamp}{target.suffix}")
    fd, tmp = tempfile.mkstemp(prefix=f".{target.name}.", suffix=".tmp", dir=target.parent)
    try:
        with os.fdopen(fd, "w", encoding="utf-8") as handle:
            json.dump(payload, handle, ensure_ascii=False, indent=2)
            handle.flush(); os.fsync(handle.fileno())
        os.replace(tmp, target)
    finally:
        if os.path.exists(tmp): os.unlink(tmp)