import logging
import json

from threading import Event, Lock

from app import app
from data.model import db
from data.database import CloseForLongOperation
from workers.worker import Worker

logger = logging.getLogger(__name__)

class JobException(Exception):
  """ A job exception is an exception that is caused by something being malformed in the job. When
      a worker raises this exception the job will be terminated and the retry will not be returned
      to the queue. """
  pass


class WorkerUnhealthyException(Exception):
  """ When this exception is raised, the worker is no longer healthy and will not accept any more
      work. When this is raised while processing a queue item, the item should be returned to the
      queue along with another retry. """
  pass

class QueueWorker(Worker):
  def __init__(self, queue, poll_period_seconds=30, reservation_seconds=300,
               watchdog_period_seconds=60, retry_after_seconds=300):
    super(QueueWorker, self).__init__()

    self._poll_period_seconds = poll_period_seconds
    self._reservation_seconds = reservation_seconds
    self._watchdog_period_seconds = watchdog_period_seconds
    self._retry_after_seconds = retry_after_seconds
    self._stop = Event()
    self._terminated = Event()
    self._queue = queue
    self._current_item_lock = Lock()
    self.current_queue_item = None

    # Add the various operations.
    self.add_operation(self.poll_queue, self._poll_period_seconds)
    self.add_operation(self.update_queue_metrics, 60)
    self.add_operation(self.run_watchdog, self._watchdog_period_seconds)

  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 _close_db_handle(self):
    if not db.is_closed():
      logger.debug('Disconnecting from database.')
      db.close()

  def extend_processing(self, seconds_from_now):
    with self._current_item_lock:
      if self.current_queue_item is not None:
        self._queue.extend_processing(self.current_queue_item, seconds_from_now)

  def run_watchdog(self):
    logger.debug('Running watchdog.')
    try:
      self.watchdog()
    except WorkerUnhealthyException as exc:
      logger.error('The worker has encountered an error via watchdog and will not take new jobs')
      logger.error(exc.message)
      self.mark_current_incomplete(restore_retry=True)
      self._stop.set()

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

    with self._current_item_lock:
      self.current_queue_item = self._queue.get(processing_time=self._reservation_seconds)

    while True:
      # Retrieve the current item in the queue over which to operate. We do so under
      # a lock to make sure we are always retrieving an item when in a healthy state.
      current_queue_item = None
      with self._current_item_lock:
        current_queue_item = self.current_queue_item
        if current_queue_item is None:
          break

      logger.debug('Queue gave us some work: %s', current_queue_item.body)
      job_details = json.loads(current_queue_item.body)

      try:
        with CloseForLongOperation(app.config):
          self.process_queue_item(job_details)

        self.mark_current_complete()

      except JobException as jex:
        logger.warning('An error occurred processing request: %s', current_queue_item.body)
        logger.warning('Job exception: %s', jex)
        self.mark_current_incomplete(restore_retry=False)

      except WorkerUnhealthyException as exc:
        logger.error('The worker has encountered an error via the job and will not take new jobs')
        logger.error(exc.message)
        self.mark_current_incomplete(restore_retry=True)
        self._stop.set()

      if not self._stop.is_set():
        with self._current_item_lock:
          self.current_queue_item = self._queue.get(processing_time=self._reservation_seconds)

    if not self._stop.is_set():
      logger.debug('No more work.')

  def update_queue_metrics(self):
    self._queue.update_metrics()

  def mark_current_incomplete(self, restore_retry=False):
    with self._current_item_lock:
      if self.current_queue_item is not None:
        self._queue.incomplete(self.current_queue_item, restore_retry=restore_retry,
                               retry_after=self._retry_after_seconds)
        self.current_queue_item = None

  def mark_current_complete(self):
    with self._current_item_lock:
      if self.current_queue_item is not None:
        self._queue.complete(self.current_queue_item)
        self.current_queue_item = None

  def ungracefully_terminated(self):
    # Give back the retry that we took for this queue item so that if it were down to zero
    # retries it will still be picked up by another worker
    self.mark_current_incomplete()