import logging
import threading
import time

logger = logging.getLogger(__name__)

SUBMIT_TIMEOUT = 3
PING_TIMEOUT = 2
WORKER_CHECK_TTL = 30  # worker 探测结果缓存时长(秒)，避免每次请求都阻塞 2s

_worker_cache = {'checked_at': 0.0, 'available': None}


def _worker_available(task, timeout=PING_TIMEOUT):
    """探测是否存在存活的 Celery worker（带 TTL 缓存）"""
    now = time.time()
    if _worker_cache['available'] is not None and now - _worker_cache['checked_at'] < WORKER_CHECK_TTL:
        return _worker_cache['available']
    try:
        inspector = task.app.control.inspect(timeout=timeout)
        available = bool(inspector.ping())
    except Exception:
        available = False
    _worker_cache['checked_at'] = now
    _worker_cache['available'] = available
    return available


def _run_with_timeout(func, args, kwargs, timeout):
    result_holder = {}

    def target():
        try:
            result_holder['result'] = func(*args, **kwargs)
        except Exception as exc:
            result_holder['exception'] = exc

    thread = threading.Thread(target=target, daemon=True)
    thread.start()
    thread.join(timeout)
    if thread.is_alive():
        raise TimeoutError('task submission exceeded %ds' % timeout)
    if 'exception' in result_holder:
        raise result_holder['exception']
    return result_holder.get('result')


def submit_task(task, *args, **kwargs):
    """发送任务，优先异步提交；无可用 worker 或超时/异常时降级为同步执行"""
    timeout = kwargs.pop('_timeout', SUBMIT_TIMEOUT)
    if not _worker_available(task):
        logger.info(
            'submit_task: no celery worker available, run synchronously: task=%s',
            getattr(task, 'name', task),
        )
        try:
            return task.apply(args, kwargs)
        except Exception as exc:
            logger.error(
                'submit_task eager fallback failed: task=%s err=%s',
                getattr(task, 'name', task), exc,
            )
            return None
    try:
        # task.apply_async(args, kwargs) 的正确传参方式
        return _run_with_timeout(task.apply_async, (args, kwargs), {}, timeout)
    except Exception as exc:
        logger.warning(
            'submit_task fallback: task=%s args=%r err=%s',
            getattr(task, 'name', task), args, exc,
        )
        try:
            return task.apply(args, kwargs)
        except Exception as exc2:
            logger.error(
                'submit_task eager fallback failed: task=%s err=%s',
                getattr(task, 'name', task), exc2,
            )
        return None


def safe_submit(task, *args, fallback=None, **kwargs):
    try:
        result = submit_task(task, *args, **kwargs)
        return result if result is not None else fallback
    except Exception:
        return fallback