"""Трекер созданных инстансов — по юзеру и стенду: /tmp/instances-{client_id}-{stand}.json."""
import fcntl
import json
import os
import time


def _path(client_id, stand):
    return f"/tmp/instances-{client_id}-{stand}.json"


def _acquire_lock(fd):
    """LOCK_EX с таймаутом 2 секунды (LOCK_NB + retry)."""
    deadline = time.time() + 2
    while True:
        try:
            fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
            return True
        except BlockingIOError:
            if time.time() >= deadline:
                return False
            time.sleep(0.05)


def _locked_read(path):
    """Читает файл под эксклюзивной блокировкой, пустой dict если нет."""
    try:
        fd = os.open(path, os.O_RDWR | os.O_CREAT, 0o644)
    except OSError:
        return {}
    try:
        if not _acquire_lock(fd):
            return {}
        try:
            data = os.read(fd, 65536)
            if data:
                return json.loads(data.decode("utf-8"))
        except (json.JSONDecodeError, UnicodeDecodeError):
            pass
        return {}
    finally:
        fcntl.flock(fd, fcntl.LOCK_UN)
        os.close(fd)


def _locked_write(path, data):
    """Пишет файл под эксклюзивной блокировкой."""
    try:
        fd = os.open(path, os.O_RDWR | os.O_CREAT, 0o644)
    except OSError:
        return
    try:
        if not _acquire_lock(fd):
            return
        os.lseek(fd, 0, 0)
        os.ftruncate(fd, 0)
        os.write(fd, json.dumps(data, indent=2).encode("utf-8"))
    finally:
        fcntl.flock(fd, fcntl.LOCK_UN)
        os.close(fd)


def add(client_id, stand, instance_uid, svc_id, display_name):
    p = _path(client_id, stand)
    data = _locked_read(p)
    data[instance_uid] = {
        "svcId": svc_id,
        "displayName": display_name,
        "instanceUid": instance_uid,
    }
    _locked_write(p, data)


def remove(client_id, stand, instance_uid):
    p = _path(client_id, stand)
    data = _locked_read(p)
    data.pop(instance_uid, None)
    _locked_write(p, data)


def list_all(client_id, stand):
    return list(_locked_read(_path(client_id, stand)).values())