from datetime import datetime, timedelta

from data.database import QueueItem, db, db_for_update
from util.morecollections import AttrDict


MINIMUM_EXTENSION = timedelta(seconds=20)


class WorkQueue(object):
  def __init__(self, queue_name, transaction_factory,
               canonical_name_match_list=None, reporter=None):
    self._queue_name = queue_name
    self._reporter = reporter
    self._transaction_factory = transaction_factory
    self._currently_processing = False

    if canonical_name_match_list is None:
      self._canonical_name_match_list = []
    else:
      self._canonical_name_match_list = canonical_name_match_list

  @staticmethod
  def _canonical_name(name_list):
    return '/'.join(name_list) + '/'

  def _running_jobs(self, now, name_match_query):
    return (QueueItem
            .select(QueueItem.queue_name)
            .where(QueueItem.available == False,
                   QueueItem.processing_expires > now,
                   QueueItem.queue_name ** name_match_query))

  def _available_jobs(self, now, name_match_query):
    return (QueueItem
            .select()
            .where(QueueItem.queue_name ** name_match_query, QueueItem.available_after <= now,
                   ((QueueItem.available == True) | (QueueItem.processing_expires <= now)),
                   QueueItem.retries_remaining > 0))

  def _available_jobs_not_running(self, now, name_match_query, running_query):
    return (self
            ._available_jobs(now, name_match_query)
            .where(~(QueueItem.queue_name << running_query)))

  def _name_match_query(self):
    return '%s%%' % self._canonical_name([self._queue_name] + self._canonical_name_match_list)

  def _item_by_id_for_update(self, queue_id):
    return db_for_update(QueueItem.select().where(QueueItem.id == queue_id)).get()

  def update_metrics(self):
    if self._reporter is None:
      return

    with self._transaction_factory(db):
      now = datetime.utcnow()
      name_match_query = self._name_match_query()

      running_query = self._running_jobs(now, name_match_query)
      running_count = running_query.distinct().count()

      available_query = self._available_jobs_not_running(now, name_match_query, running_query)
      available_count = available_query.select(QueueItem.queue_name).distinct().count()

    self._reporter(self._currently_processing, running_count, running_count + available_count)

  def put(self, canonical_name_list, message, available_after=0, retries_remaining=5):
    """
    Put an item, if it shouldn't be processed for some number of seconds,
    specify that amount as available_after.
    """

    params = {
      'queue_name': self._canonical_name([self._queue_name] + canonical_name_list),
      'body': message,
      'retries_remaining': retries_remaining,
    }

    available_date = datetime.utcnow() + timedelta(seconds=available_after or 0)
    params['available_after'] = available_date

    with self._transaction_factory(db):
      return QueueItem.create(**params)

  def get(self, processing_time=300):
    """
    Get an available item and mark it as unavailable for the default of five
    minutes. The result of this method must always be composed of simple
    python objects which are JSON serializable for network portability reasons.
    """
    now = datetime.utcnow()

    name_match_query = self._name_match_query()

    running = self._running_jobs(now, name_match_query)
    avail = self._available_jobs_not_running(now, name_match_query, running)

    item = None
    try:
      db_item_candidate = avail.order_by(QueueItem.id).get()

      with self._transaction_factory(db):
        still_available_query = (db_for_update(self
                                               ._available_jobs(now, name_match_query)
                                               .where(QueueItem.id == db_item_candidate.id)))

        db_item = still_available_query.get()
        db_item.available = False
        db_item.processing_expires = now + timedelta(seconds=processing_time)
        db_item.retries_remaining -= 1
        db_item.save()

        item = AttrDict({
          'id': db_item.id,
          'body': db_item.body,
          'retries_remaining': db_item.retries_remaining
        })

        self._currently_processing = True
    except QueueItem.DoesNotExist:
      self._currently_processing = False

    # Return a view of the queue item rather than an active db object
    return item

  def complete(self, completed_item):
    with self._transaction_factory(db):
      completed_item_obj = self._item_by_id_for_update(completed_item.id)
      completed_item_obj.delete_instance()
      self._currently_processing = False

  def incomplete(self, incomplete_item, retry_after=300, restore_retry=False):
    with self._transaction_factory(db):
      retry_date = datetime.utcnow() + timedelta(seconds=retry_after)
      incomplete_item_obj = self._item_by_id_for_update(incomplete_item.id)
      incomplete_item_obj.available_after = retry_date
      incomplete_item_obj.available = True

      if restore_retry:
        incomplete_item_obj.retries_remaining += 1

      incomplete_item_obj.save()
      self._currently_processing = False
      return incomplete_item_obj.retries_remaining > 0

  def extend_processing(self, item, seconds_from_now, minimum_extension=MINIMUM_EXTENSION):
    with self._transaction_factory(db):
      queue_item = self._item_by_id_for_update(item.id)
      new_expiration = datetime.utcnow() + timedelta(seconds=seconds_from_now)

      # Only actually write the new expiration to the db if it moves the expiration some minimum
      if new_expiration - queue_item.processing_expires > minimum_extension:
        queue_item.processing_expires = new_expiration
        queue_item.save()