import logging
import signal
import sys
import socket
import time

from datetime import datetime, timedelta
from functools import wraps
from random import randint
from threading import Event

from apscheduler.schedulers.background import BackgroundScheduler
from raven import Client

from app import app
from data.database import UseThenDisconnect
from util.log import logfile_path

logger = logging.getLogger(__name__)


def with_exponential_backoff(backoff_multiplier=10, max_backoff=3600, max_retries=10):
  def inner(func):
    """ Decorator to retry the operation with exponential backoff if it raised an exception.
        Waits 2^attempts * `backoff_multiplier`, up to `max_backoff`, up to `max_retries` number of time,
        then re-raise the exception.
    """
    def wrapper(*args, **kwargs):
      attempts = 0
      backoff = 0

      while True:
        next_backoff = 2**attempts * backoff_multiplier
        backoff = min(next_backoff, max_backoff)
        attempts += 1

        try:
          return func(*args, **kwargs)
        except Exception as e:
          if max_retries is not None and attempts == max_retries:
            raise e

        logger.exception('Operation raised exception, retrying in %d seconds', backoff)
        time.sleep(backoff)

    return wrapper
  return inner


class Worker(object):
  """ Base class for workers which perform some work periodically. """
  def __init__(self):
    self._sched = BackgroundScheduler()
    self._operations = []
    self._stop = Event()
    self._terminated = Event()
    self._raven_client = None

    if app.config.get('EXCEPTION_LOG_TYPE', 'FakeSentry') == 'Sentry':
      worker_name = '%s:worker-%s' % (socket.gethostname(), self.__class__.__name__)
      self._raven_client = Client(app.config.get('SENTRY_DSN', ''), name=worker_name)

  def is_healthy(self):
    return not self._stop.is_set()

  def is_terminated(self):
    return self._terminated.is_set()

  def ungracefully_terminated(self):
    """ Method called when the worker has been terminated in an ungraceful fashion. """
    pass

  def add_operation(self, operation_func, operation_sec):
    @wraps(operation_func)
    def _operation_func():
      try:
        with UseThenDisconnect(app.config):
          return operation_func()
      except Exception:
        logger.exception('Operation raised exception')
        if self._raven_client:
          logger.debug('Logging exception to Sentry')
          self._raven_client.captureException()

    self._operations.append((_operation_func, operation_sec))

  def _setup_and_wait_for_shutdown(self):
    signal.signal(signal.SIGTERM, self.terminate)
    signal.signal(signal.SIGINT, self.terminate)

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

  def start(self):
    logging.config.fileConfig(logfile_path(debug=False), disable_existing_loggers=False)

    if not app.config.get('SETUP_COMPLETE', False):
      logger.info('Product setup is not yet complete; skipping worker startup')
      self._setup_and_wait_for_shutdown()
      return

    if app.config.get('REGISTRY_STATE', 'normal') == 'readonly':
      logger.info('Product is in read-only mode; skipping worker startup')
      self._setup_and_wait_for_shutdown()
      return

    logger.debug('Scheduling worker.')

    self._sched.start()
    for operation_func, operation_sec in self._operations:
      start_date = datetime.now() + timedelta(seconds=0.001)
      if app.config.get('STAGGER_WORKERS'):
        start_date += timedelta(seconds=randint(1, operation_sec))
      logger.debug('First run scheduled for %s', start_date)
      self._sched.add_job(operation_func, 'interval', seconds=operation_sec,
                          start_date=start_date, max_instances=1)


    self._setup_and_wait_for_shutdown()

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

    self._terminated.set()

  def terminate(self, signal_num=None, stack_frame=None, graceful=False):
    if self._terminated.is_set():
      sys.exit(1)

    else:
      logger.debug('Shutting down worker.')
      self._stop.set()

      if not graceful:
        self.ungracefully_terminated()

  def join(self):
    self.terminate(graceful=True)