# -*- coding: utf-8 -*-
from __future__ import unicode_literals

import logging
import threading
import time

log = logging.getLogger(__name__)

CADENCE = 1.0  # in seconds
SHUTDOWN_TIMEOUT = 5
_should_poll = threading.Event()
_task = None


class _Poller(threading.Thread):

    def __init__(self, should_poll, *args, **kw):

        super(_Poller, self).__init__(*args, **kw)

        # threading.Event instance that controls thread lifecycle
        self._should_poll = should_poll

        # Make this a daemon thread so it will die with the main thread
        self.daemon = True

    def run(self):
        """ Actually run the poller loop.
        """

        while self._should_poll.isSet():
            try:
                self._execute()
            except Exception:
                log.exception("poller encountered an exception")
            finally:
                time.sleep(CADENCE)

        log.info("poller run loop has exited")

    def _execute(self):
        """ Execute a poller iteration
        """

        # insert poller logic here
        pass


def start():
    """ start polling
    """

    global _task

    if _task is not None:
        # Shutdown an existing poller
        log.warning("found an existing poller, shutting it down")
        _task.shutdown(timeout=SHUTDOWN_TIMEOUT)

    _should_poll.set()
    _task = _Poller(_should_poll)

    log.info("starting to poll")
    _task.start()


def stop():
    """ stop polling
    """

    global _task

    _should_poll.clear()

    if _task is not None:
        log.info("poller is shutting down...")
        _task.join(timeout=SHUTDOWN_TIMEOUT)