"""
Межпроцессная блокировка для POST /api/sync/pull по node_id.

threading.Lock в SyncRuntime не действует между процессами (Flask reloader, Gunicorn
workers): два параллельных pull с одним client_id → два process_pull на SQLite и зависание.
На POSIX используем flock на отдельном файле; на Windows — не используем (остаётся thread lock).
"""

from __future__ import annotations

import hashlib
import os
import sys
import tempfile
import time
from pathlib import Path
from typing import BinaryIO, Optional

_HAVE_FCNTL = False
if sys.platform != "win32":
    try:
        import fcntl  # noqa: F401

        _HAVE_FCNTL = True
    except ImportError:
        pass


def ipc_pull_supported() -> bool:
    return _HAVE_FCNTL


def _lock_file_path(client_id: str) -> Path:
    cid = (client_id or "").strip()
    h = hashlib.sha256(cid.encode("utf-8")).hexdigest()[:32]
    base = Path(os.getenv("WESP_SYNC_PULL_IPC_LOCK_DIR", tempfile.gettempdir())) / "wesp-sync-pull"
    base.mkdir(parents=True, exist_ok=True)
    return base / f"{h}.lock"


def ipc_pull_acquire(client_id: str, timeout: float) -> Optional[BinaryIO]:
    """exclusive flock; при таймауте — None. Не вызывать, если не ipc_pull_supported()."""
    import fcntl

    cid = (client_id or "").strip()
    if not cid:
        return None
    path = _lock_file_path(cid)
    fp = open(path, "a+b")
    deadline = time.monotonic() + max(0.0, timeout)
    try:
        while True:
            try:
                fcntl.flock(fp.fileno(), fcntl.LOCK_EX | fcntl.LOCK_NB)
                return fp
            except BlockingIOError:
                if time.monotonic() >= deadline:
                    fp.close()
                    return None
                time.sleep(0.05)
    except Exception:
        try:
            fp.close()
        except OSError:
            pass
        raise


def ipc_pull_release(fp: Optional[BinaryIO]) -> None:
    if not fp or not _HAVE_FCNTL:
        return
    import fcntl

    try:
        fcntl.flock(fp.fileno(), fcntl.LOCK_UN)
    except OSError:
        pass
    try:
        fp.close()
    except OSError:
        pass