from multiprocessing import Process, Queue
from collections import namedtuple

import logging
import multiprocessing
import time
import sys
import traceback


logger = multiprocessing.log_to_stderr()
logger.setLevel(logging.INFO)


class QueueProcess(object):
  """ Helper class which invokes a worker in a process to produce
      data for one (or more) queues.
  """
  def __init__(self, get_producer, chunk_size, max_size, args, finished=None):
    self._get_producer = get_producer
    self._queues = []
    self._chunk_size = chunk_size
    self._max_size = max_size
    self._args = args or []
    self._finished = finished

  def create_queue(self):
    """ Adds a multiprocessing queue to the list of queues. Any queues added
        will have the data produced appended.
    """
    queue = Queue(self._max_size / self._chunk_size)
    self._queues.append(queue)
    return queue

  @staticmethod
  def run_process(target, args, finished=None):
    def _target(tar, arg, fin):
      try:
        tar(*args)
      finally:
        if fin:
          fin()

    Process(target=_target, args=(target, args, finished)).start()

  def run(self):
    # Important! gipc is used here because normal multiprocessing does not work
    # correctly with gevent when we sleep.
    args = (self._get_producer, self._queues, self._chunk_size, self._args)
    QueueProcess.run_process(_run, args, finished=self._finished)


QueueResult = namedtuple('QueueResult', ['data', 'exception'])

def _run(get_producer, queues, chunk_size, args):
  producer = get_producer(*args)
  while True:
    try:
      result = QueueResult(producer(chunk_size) or None, None)
    except Exception as ex:
      message = '%s\n%s' % (ex.message, "".join(traceback.format_exception(*sys.exc_info())))
      result = QueueResult(None, Exception(message))

    for queue in queues:
      try:
        queue.put(result, block=True)
      except Exception as ex:
        logger.exception('Exception writing to queue.')
        return

    # Terminate the producer loop if the data produced is empty or an exception occurred.
    if result.data is None or result.exception is not None:
      break

    # Important! This allows the thread that writes the queue data to the pipe
    # to do so. Otherwise, this hangs.
    time.sleep(0)