import calendar
import sys

from email.utils import formatdate
from apscheduler.schedulers.background import BackgroundScheduler
from datetime import datetime, timedelta

from data import model


class ExpirationScheduler(object):
  def __init__(self, utc_create_notifications_date, utc_terminate_processes_date):
    self._scheduler = BackgroundScheduler()
    self._termination_date = utc_terminate_processes_date

    soon = datetime.now() + timedelta(seconds=1)

    if utc_create_notifications_date > datetime.utcnow():
      self._scheduler.add_job(model.delete_all_notifications_by_kind, 'date', run_date=soon,
                              args=['expiring_license'])

      local_notifications_date = self._utc_to_local(utc_create_notifications_date)
      self._scheduler.add_job(self._generate_notifications, 'date',
                              run_date=local_notifications_date)
    else:
      self._scheduler.add_job(self._generate_notifications, 'date', run_date=soon)

    local_termination_date = self._utc_to_local(utc_terminate_processes_date)
    self._scheduler.add_job(self._terminate, 'date', run_date=local_termination_date)

  @staticmethod
  def _format_date(date):
    """ Output an RFC822 date format. """
    if date is None:
      return None
    return formatdate(calendar.timegm(date.utctimetuple()))

  @staticmethod
  def _utc_to_local(utc_dt):
    # get integer timestamp to avoid precision lost
    timestamp = calendar.timegm(utc_dt.timetuple())
    local_dt = datetime.fromtimestamp(timestamp)
    return local_dt.replace(microsecond=utc_dt.microsecond)

  def _generate_notifications(self):
    for user in model.get_active_users():
      model.create_unique_notification('expiring_license', user,
                                       {'expires_at': self._format_date(self._termination_date)})

  @staticmethod
  def _terminate():
    sys.exit(1)

  def start(self):
    self._scheduler.start()