import logging
import json
import signal

from threading import Event
from apscheduler.scheduler import Scheduler


logger = logging.getLogger(__name__)


class Worker(object):
  def __init__(self, queue, poll_period_seconds=30, reservation_seconds=300,
               watchdog_period_seconds=60):
    self._sched = Scheduler()
    self._poll_period_seconds = poll_period_seconds
    self._reservation_seconds = reservation_seconds
    self._watchdog_period_seconds = watchdog_period_seconds
    self._stop = Event()
    self._queue = queue

  def process_queue_item(self, job_details):
    """ Return True if complete, False if it should be retried. """
    raise NotImplementedError('Workers must implement run.')

  def watchdog(self):
    """ Function that gets run once every watchdog_period_seconds. """
    pass

  def poll_queue(self):
    logger.debug('Getting work item from queue.')

    item = self._queue.get()
    while item:
      logger.debug('Queue gave us some work: %s' % item.body)

      job_details = json.loads(item.body)

      if self.process_queue_item(job_details):
        self._queue.complete(item)
      else:
        logger.warning('An error occurred processing request: %s' % item.body)
        self._queue.incomplete(item)

      item = self._queue.get(processing_time=self._reservation_seconds)

    logger.debug('No more work.')

  def start(self):
    logger.debug("Scheduling worker.")

    self._sched.start()
    self._sched.add_interval_job(self.poll_queue, seconds=self._poll_period_seconds)
    self._sched.add_interval_job(self.watchdog, seconds=self._watchdog_period_seconds)

    signal.signal(signal.SIGTERM, self.join)
    signal.signal(signal.SIGINT, self.join)   

    while not self._stop.wait(1):
      pass

    logger.debug('Waiting for running tasks to complete.')
    self._sched.shutdown()
    logger.debug('Finished.')

  def join(self, signal_num=None, stack_frame=None):
    logger.debug('Shutting down worker gracefully.')
    self._stop.set()