"""File locking and atomic JSON helpers."""
import fcntl
import json
import os
from contextlib import contextmanager
from pathlib import Path


@contextmanager
def locked_file(path: Path):
    path.parent.mkdir(parents=True, exist_ok=True)
    with open(path, "a+", encoding="utf-8") as f:
        fcntl.flock(f.fileno(), fcntl.LOCK_EX)
        f.seek(0)
        yield f
        f.flush()
        os.fsync(f.fileno())
        fcntl.flock(f.fileno(), fcntl.LOCK_UN)


def atomic_write_json(path: Path, data: dict):
    path.parent.mkdir(parents=True, exist_ok=True)
    tmp = path.with_suffix(path.suffix + ".tmp")
    tmp.write_text(json.dumps(data, indent=2, ensure_ascii=False), encoding="utf-8")
    os.replace(tmp, path)


def load_json_locked(path: Path, lock_path: Path, default):
    with locked_file(lock_path):
        if not path.exists():
            return default
        try:
            return json.loads(path.read_text(encoding="utf-8"))
        except Exception:
            return default


def save_json_locked(path: Path, lock_path: Path, data: dict):
    with locked_file(lock_path):
        atomic_write_json(path, data)