"""
原子 I/O 模块 — 消除 V1 5 份 _json_dump/_json_load 重复。
每次写入使用 tempfile + os.replace() 保证原子性，写入前自动备份。
"""

from __future__ import annotations

import contextlib
import json
import logging
import os
import tempfile
from pathlib import Path

logger = logging.getLogger(__name__)


def atomic_json_write(path: Path, data: dict | list, indent: int = 2) -> None:
    """POSIX 原子写入：tempfile + os.replace()。写入前自动备份旧文件为 .bak（单级轮转）。"""
    path.parent.mkdir(parents=True, exist_ok=True)

    # 备份旧文件
    if path.exists():
        bak = path.with_suffix(path.suffix + ".bak")
        try:
            os.replace(str(path), str(bak))
        except OSError as exc:
            logger.warning("backup %s -> %s failed: %s", path, bak, exc)

    fd, tmp = tempfile.mkstemp(dir=path.parent, suffix=".tmp")
    try:
        os.write(fd, json.dumps(data, indent=indent, ensure_ascii=False).encode("utf-8"))
        os.close(fd)
        os.replace(tmp, path)
    except BaseException:
        with contextlib.suppress(OSError):
            os.unlink(tmp)
        raise


def safe_json_load(path: Path) -> dict | list | None:
    """安全加载：处理损坏文件，自动从 .bak 恢复。文件不存在返回 None。"""
    try:
        return json.loads(path.read_text("utf-8"))
    except FileNotFoundError:
        return None
    except (json.JSONDecodeError, UnicodeDecodeError):
        bak = path.with_suffix(path.suffix + ".bak")
        if bak.exists():
            logger.warning("corrupt %s, restoring from %s", path, bak)
            return json.loads(bak.read_text("utf-8"))
        logger.error("corrupt %s with no backup", path)
        return None