import httplib
import httplib2
import random
import time

from googleapiclient.errors import HttpError

# Explicitly tell the underlying HTTP transport library not to retry, since
# we are handling retry logic ourselves.
httplib2.RETRIES = 1

# Maximum number of times to retry before giving up.
MAX_RETRIES = 10

# Always retry when these exceptions are raised.
RETRIABLE_EXCEPTIONS = (httplib2.HttpLib2Error, IOError, httplib.NotConnected,
  httplib.IncompleteRead, httplib.ImproperConnectionState,
  httplib.CannotSendRequest, httplib.CannotSendHeader,
  httplib.ResponseNotReady, httplib.BadStatusLine)

# Always retry when an apiclient.errors.HttpError with one of these status
# codes is raised.
RETRIABLE_STATUS_CODES = [500, 502, 503, 504]

# This method implements an exponential backoff strategy to resume a
# failed upload.
def resumable_upload(request):
  response = None
  error = None
  retry = 0
  while response is None:
    try:
      status, response = request.next_chunk()
      if response is not None:
        return response
    except HttpError, e:
      if e.resp.status in RETRIABLE_STATUS_CODES:
        error = "A retriable HTTP error %d occurred:\n%s" % (e.resp.status,
                                                             e.content)
      else:
        raise
    except RETRIABLE_EXCEPTIONS, e:
      error = "A retriable error occurred: %s" % e

    if error is not None:
      print error
      retry += 1
      if retry > MAX_RETRIES:
        raise Exception("No longer attempting to retry.")

      max_sleep = 2 ** retry
      sleep_seconds = random.random() * max_sleep
      print "Sleeping %f seconds and then retrying..." % sleep_seconds
      time.sleep(sleep_seconds)
