#!/usr/bin/env python
#
# Copyright 2007 Google Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#


"""Task Queue API.

Enables an application to queue background work for itself. Work is done
through webhooks that process tasks pushed from a queue, or workers that
manually pull tasks from a queue. In push queues, Tasks will execute in
best-effort order of ETA. Webhooks that fail will cause tasks to be retried
at a later time. In pull queues, workers are responsible of leasing tasks for
processing and deleting the tasks when completed. Multiple queues may exist
with independent throttling controls.

Webhook URLs may be specified directly for push Tasks, or the default URL scheme
may be used, which will translate Task names into URLs relative to a Queue's
base path. A default queue is also provided for simple usage.
"""


__all__ = [

    'BadTaskStateError', 'BadTransactionState', 'BadTransactionStateError',
    'DatastoreError', 'DuplicateTaskNameError', 'Error', 'InternalError',
    'InvalidQueueError', 'InvalidQueueNameError', 'InvalidTaskError',
    'InvalidTaskNameError', 'InvalidUrlError', 'PermissionDeniedError',
    'TaskAlreadyExistsError', 'TaskTooLargeError', 'TombstonedTaskError',
    'TooManyTasksError', 'TransientError', 'UnknownQueueError',
    'InvalidLeaseTimeError', 'InvalidMaxTasksError',
    'InvalidQueueModeError', 'TransactionalRequestTooLargeError',
    'TaskLeaseExpiredError', 'QueuePausedError',

    'MAX_QUEUE_NAME_LENGTH', 'MAX_TASK_NAME_LENGTH', 'MAX_TASK_SIZE_BYTES',
    'MAX_PULL_TASK_SIZE_BYTES', 'MAX_PUSH_TASK_SIZE_BYTES',
    'MAX_URL_LENGTH',

    'Queue', 'Task', 'TaskRetryOptions', 'add']


import calendar
import cgi
import datetime
import math
import os
import re
import time
import urllib
import urlparse

from google.appengine.api import apiproxy_stub_map
from google.appengine.api import namespace_manager
from google.appengine.api import urlfetch
from google.appengine.api.taskqueue import taskqueue_service_pb
from google.appengine.runtime import apiproxy_errors


class Error(Exception):
  """Base-class for exceptions in this module."""


class UnknownQueueError(Error):
  """The queue specified is unknown."""


class TransientError(Error):
  """There was a transient error while accessing the queue.

  Please Try again later.
  """


class InternalError(Error):
  """There was an internal error while accessing this queue.

  If this problem continues, please contact the App Engine team through
  our support forum with a description of your problem.
  """


class InvalidTaskError(Error):
  """The task's parameters, headers, or method is invalid."""


class InvalidTaskNameError(InvalidTaskError):
  """The task's name is invalid."""


class TaskTooLargeError(InvalidTaskError):
  """The task is too large with its headers and payload."""


class TaskAlreadyExistsError(InvalidTaskError):
  """Task already exists. It has not yet run."""


class TombstonedTaskError(InvalidTaskError):
  """Task has been tombstoned."""


class InvalidUrlError(InvalidTaskError):
  """The task's relative URL is invalid."""


class BadTaskStateError(Error):
  """The task is in the wrong state for the requested operation."""


class InvalidQueueError(Error):
  """The Queue's configuration is invalid."""


class InvalidQueueNameError(InvalidQueueError):
  """The Queue's name is invalid."""


class _RelativeUrlError(Error):
  """The relative URL supplied is invalid."""


class PermissionDeniedError(Error):
  """The requested operation is not allowed for this app."""


class DuplicateTaskNameError(Error):
  """The add arguments contain tasks with identical names."""


class TooManyTasksError(Error):
  """Too many tasks were present in a single function call."""


class DatastoreError(Error):
  """There was a datastore error while accessing the queue."""


class BadTransactionStateError(Error):
  """The state of the current transaction does not permit this operation."""


class InvalidTaskRetryOptionsError(Error):
  """The task retry configuration is invalid."""


class InvalidLeaseTimeError(Error):
  """The lease time period is invalid."""


class InvalidMaxTasksError(Error):
  """The requested max tasks in lease_tasks is invalid."""


class InvalidQueueModeError(Error):
  """Invoking PULL queue operation on a PUSH queue or vice versa."""


class TransactionalRequestTooLargeError(TaskTooLargeError):
  """The total size of this transaction (including tasks) was too large."""


class TaskLeaseExpiredError(Error):
  """The task lease could not be renewed because it had already expired."""


class QueuePausedError(Error):
  """The queue is paused and cannot process modify task lease requests."""


BadTransactionState = BadTransactionStateError

MAX_QUEUE_NAME_LENGTH = 100

MAX_PULL_TASK_SIZE_BYTES = 2 ** 20

MAX_PUSH_TASK_SIZE_BYTES = 100 * (2 ** 10)

MAX_TASK_NAME_LENGTH = 500

MAX_TASK_SIZE_BYTES = MAX_PUSH_TASK_SIZE_BYTES

MAX_TASKS_PER_ADD = 100

MAX_TRANSACTIONAL_REQUEST_SIZE_BYTES = 2 ** 20


MAX_URL_LENGTH = 2083

MAX_TASKS_PER_LEASE = 1000

MAX_LEASE_SECONDS = 3600 * 24 * 7

_DEFAULT_QUEUE = 'default'

_DEFAULT_QUEUE_PATH = '/_ah/queue'

_METHOD_MAP = {
    'GET': taskqueue_service_pb.TaskQueueAddRequest.GET,
    'POST': taskqueue_service_pb.TaskQueueAddRequest.POST,
    'HEAD': taskqueue_service_pb.TaskQueueAddRequest.HEAD,
    'PUT': taskqueue_service_pb.TaskQueueAddRequest.PUT,
    'DELETE': taskqueue_service_pb.TaskQueueAddRequest.DELETE,
}

_NON_POST_HTTP_METHODS = frozenset(['GET', 'HEAD', 'PUT', 'DELETE'])

_BODY_METHODS = frozenset(['POST', 'PUT', 'PULL'])

_TASK_NAME_PATTERN = r'^[a-zA-Z0-9_-]{1,%s}$' % MAX_TASK_NAME_LENGTH

_TASK_NAME_RE = re.compile(_TASK_NAME_PATTERN)

_QUEUE_NAME_PATTERN = r'^[a-zA-Z0-9-]{1,%s}$' % MAX_QUEUE_NAME_LENGTH

_QUEUE_NAME_RE = re.compile(_QUEUE_NAME_PATTERN)

_ERROR_MAPPING = {
    taskqueue_service_pb.TaskQueueServiceError.UNKNOWN_QUEUE: UnknownQueueError,
    taskqueue_service_pb.TaskQueueServiceError.TRANSIENT_ERROR:
        TransientError,
    taskqueue_service_pb.TaskQueueServiceError.INTERNAL_ERROR: InternalError,
    taskqueue_service_pb.TaskQueueServiceError.TASK_TOO_LARGE:
        TaskTooLargeError,
    taskqueue_service_pb.TaskQueueServiceError.INVALID_TASK_NAME:
    InvalidTaskNameError,
        taskqueue_service_pb.TaskQueueServiceError.INVALID_QUEUE_NAME:
    InvalidQueueNameError,
    taskqueue_service_pb.TaskQueueServiceError.INVALID_URL: InvalidUrlError,
    taskqueue_service_pb.TaskQueueServiceError.INVALID_QUEUE_RATE:
        InvalidQueueError,
    taskqueue_service_pb.TaskQueueServiceError.PERMISSION_DENIED:
        PermissionDeniedError,
    taskqueue_service_pb.TaskQueueServiceError.TASK_ALREADY_EXISTS:
        TaskAlreadyExistsError,
    taskqueue_service_pb.TaskQueueServiceError.TOMBSTONED_TASK:
        TombstonedTaskError,
    taskqueue_service_pb.TaskQueueServiceError.INVALID_ETA: InvalidTaskError,
    taskqueue_service_pb.TaskQueueServiceError.INVALID_REQUEST: Error,
    taskqueue_service_pb.TaskQueueServiceError.UNKNOWN_TASK: Error,
    taskqueue_service_pb.TaskQueueServiceError.TOMBSTONED_QUEUE: Error,
    taskqueue_service_pb.TaskQueueServiceError.DUPLICATE_TASK_NAME:
        DuplicateTaskNameError,
    taskqueue_service_pb.TaskQueueServiceError.INVALID_QUEUE_MODE:
        InvalidQueueModeError,

    taskqueue_service_pb.TaskQueueServiceError.TOO_MANY_TASKS:
        TooManyTasksError,
    taskqueue_service_pb.TaskQueueServiceError.TRANSACTIONAL_REQUEST_TOO_LARGE:
        TransactionalRequestTooLargeError,
    taskqueue_service_pb.TaskQueueServiceError.TASK_LEASE_EXPIRED:
        TaskLeaseExpiredError,
    taskqueue_service_pb.TaskQueueServiceError.QUEUE_PAUSED:
        QueuePausedError

}


_PRESERVE_ENVIRONMENT_HEADERS = (
    ('X-AppEngine-Default-Namespace', 'HTTP_X_APPENGINE_DEFAULT_NAMESPACE'),)


class _UTCTimeZone(datetime.tzinfo):
  """UTC timezone."""

  ZERO = datetime.timedelta(0)

  def utcoffset(self, dt):
    return self.ZERO

  def dst(self, dt):
    return self.ZERO

  def tzname(self, dt):
    return 'UTC'


_UTC = _UTCTimeZone()


def _parse_relative_url(relative_url):
  """Parses a relative URL and splits it into its path and query string.

  Args:
    relative_url: The relative URL, starting with a '/'.

  Returns:
    Tuple (path, query) where:
      path: The path in the relative URL.
      query: The query string in the URL without the '?' character.

  Raises:
    _RelativeUrlError if the relative_url is invalid for whatever reason.
  """
  if not relative_url:
    raise _RelativeUrlError('Relative URL is empty')
  (scheme, netloc, path, query, fragment) = urlparse.urlsplit(relative_url)
  if scheme or netloc:
    raise _RelativeUrlError('Relative URL may not have a scheme or location')
  if fragment:
    raise _RelativeUrlError('Relative URL may not specify a fragment')
  if not path or path[0] != '/':
    raise _RelativeUrlError('Relative URL path must start with "/"')
  return path, query


def _flatten_params(params):
  """Converts a dictionary of parameters to a list of parameters.

  Any unicode strings in keys or values will be encoded as UTF-8.

  Args:
    params: Dictionary mapping parameter keys to values. Values will be
      converted to a string and added to the list as tuple (key, value). If
      a values is iterable and not a string, each contained value will be
      added as a separate (key, value) tuple.

  Returns:
    List of (key, value) tuples.
  """
  def get_string(value):
    if isinstance(value, unicode):
      return unicode(value).encode('utf-8')
    else:


      return str(value)

  param_list = []
  for key, value in params.iteritems():
    key = get_string(key)
    if isinstance(value, basestring):
      param_list.append((key, get_string(value)))
    else:
      try:
        iterator = iter(value)
      except TypeError:
        param_list.append((key, str(value)))
      else:
        param_list.extend((key, get_string(v)) for v in iterator)

  return param_list


class TaskRetryOptions(object):
  """The options used to decide when a failed Task will be retried."""

  __CONSTRUCTOR_KWARGS = frozenset(
      ['min_backoff_seconds', 'max_backoff_seconds',
       'task_age_limit', 'max_doublings', 'task_retry_limit'])

  def __init__(self, **kwargs):
    """Initializer.

    Args:
      min_backoff_seconds: The minimum number of seconds to wait before retrying
        a task after failure. (optional)
      max_backoff_seconds: The maximum number of seconds to wait before retrying
        a task after failure. (optional)
      task_age_limit: The number of seconds after creation afterwhich a failed
        task will no longer be retried. The given value will be rounded up to
        the nearest integer. If task_retry_limit is also specified then the task
        will be retried until both limits are reached. (optional)
      max_doublings: The maximum number of times that the interval between
        failed task retries will be doubled before the increase becomes
        constant. The constant will be:
        2**(max_doublings - 1) * min_backoff_seconds. (optional)
      task_retry_limit: The maximum number of times to retry a failed task
        before giving up. If task_age_limit is specified then the task will be
        retried until both limits are reached. (optional)

    Raises:
      InvalidTaskRetryOptionsError if any of the parameters are invalid.
    """
    args_diff = set(kwargs.iterkeys()) - self.__CONSTRUCTOR_KWARGS
    if args_diff:
      raise TypeError('Invalid arguments: %s' % ', '.join(args_diff))

    self.__min_backoff_seconds = kwargs.get('min_backoff_seconds')
    if (self.__min_backoff_seconds is not None and
        self.__min_backoff_seconds < 0):
      raise InvalidTaskRetryOptionsError(
          'The minimum retry interval cannot be negative')

    self.__max_backoff_seconds = kwargs.get('max_backoff_seconds')
    if (self.__max_backoff_seconds is not None and
        self.__max_backoff_seconds < 0):
      raise InvalidTaskRetryOptionsError(
          'The maximum retry interval cannot be negative')

    if (self.__min_backoff_seconds is not None and
        self.__max_backoff_seconds is not None and
        self.__max_backoff_seconds < self.__min_backoff_seconds):
      raise InvalidTaskRetryOptionsError(
          'The maximum retry interval cannot be less than the '
          'minimum retry interval')

    self.__max_doublings = kwargs.get('max_doublings')
    if self.__max_doublings is not None and self.__max_doublings < 0:
      raise InvalidTaskRetryOptionsError(
          'The maximum number of retry interval doublings cannot be negative')

    self.__task_retry_limit = kwargs.get('task_retry_limit')
    if self.__task_retry_limit is not None and self.__task_retry_limit < 0:
      raise InvalidTaskRetryOptionsError(
          'The maximum number of retries cannot be negative')

    self.__task_age_limit = kwargs.get('task_age_limit')
    if self.__task_age_limit is not None:
      if self.__task_age_limit < 0:
        raise InvalidTaskRetryOptionsError(
            'The expiry countdown cannot be negative')
      self.__task_age_limit = int(math.ceil(self.__task_age_limit))

  @property
  def min_backoff_seconds(self):
    """The minimum number of seconds to wait before retrying a task."""
    return self.__min_backoff_seconds

  @property
  def max_backoff_seconds(self):
    """The maximum number of seconds to wait before retrying a task."""
    return self.__max_backoff_seconds

  @property
  def task_age_limit(self):
    """The number of seconds afterwhich a failed task will not be retried."""
    return self.__task_age_limit

  @property
  def max_doublings(self):
    """The number of times that the retry interval will be doubled."""
    return self.__max_doublings

  @property
  def task_retry_limit(self):
    """The number of times that a failed task will be retried."""
    return self.__task_retry_limit


class Task(object):
  """Represents a single Task on a queue."""


  __CONSTRUCTOR_KWARGS = frozenset([
      'countdown', 'eta', 'headers', 'method', 'name', 'params',
      'retry_options', 'target', 'url', '_size_check'])


  __eta_posix = None
  __target = None


  def __init__(self, payload=None, **kwargs):
    """Initializer.

    All parameters are optional.

    Args:
      payload: The payload data for this Task that will either be delivered
        to the webhook as the HTTP request body or fetched by workers for pull
        queues. This is only allowed for POST, PUT and PULL methods.
      name: Name to give the Task; if not specified, a name will be
        auto-generated when added to a queue and assigned to this object. Must
        match the _TASK_NAME_PATTERN regular expression.
      method: Method to use when accessing the webhook. Defaults to 'POST'. If
        set to 'PULL', task will not be automatically delivered to the webhook,
        instead it stays in the queue until leased.
      url: Relative URL where the webhook that should handle this task is
        located for this application. May have a query string unless this is
        a POST method. Must not be specified if method is PULL.
      headers: Dictionary of headers to pass to the webhook. Values in the
        dictionary may be iterable to indicate repeated header fields. Must not
        be specified if method is PULL.
      params: Dictionary of parameters to use for Task. For POST and PULL
        requests these params will be encoded as
        'application/x-www-form-urlencoded' and set to the payload. For all
        other methods, the parameters will be converted to a query string. Must
        not be specified if the URL already contains a query string, or the
        task already has payload.
      countdown: Time in seconds into the future that this Task should execute.
        Defaults to zero.
      eta: A datetime.datetime specifying the absolute time at which the task
        should be executed. Must not be specified if 'countdown' is specified.
        This may be timezone-aware or timezone-naive. If None, defaults to now.
        For pull tasks, no worker will be able to lease this task before the
        time indicated by eta.
      retry_options: TaskRetryOptions used to control when the task will be
        retried if it fails.
      target: The alternate version/server on which to execute this task.

    Raises:
      InvalidTaskError: if any of the parameters are invalid;
      InvalidTaskNameError: if the task name is invalid;
      InvalidUrlError: if the task URL is invalid or too long;
      TaskTooLargeError: if the task with its payload is too large.
    """
    args_diff = set(kwargs.iterkeys()) - self.__CONSTRUCTOR_KWARGS
    if args_diff:
      raise TypeError('Invalid arguments: %s' % ', '.join(args_diff))

    self.__name = kwargs.get('name')
    if self.__name and not _TASK_NAME_RE.match(self.__name):
      raise InvalidTaskNameError(
          'Task name does not match expression "%s"; found %s' %
          (_TASK_NAME_PATTERN, self.__name))

    self.__default_url, self.__relative_url, query = Task.__determine_url(
        kwargs.get('url', ''))
    self.__headers = urlfetch._CaselessDict()
    self.__headers.update(kwargs.get('headers', {}))
    self.__method = kwargs.get('method', 'POST').upper()
    self.__payload = None
    self.__retry_count = 0
    self.__queue_name = None


    size_check = kwargs.get('_size_check', True)
    params = kwargs.get('params', {})


    for header_name, environ_name in _PRESERVE_ENVIRONMENT_HEADERS:
      value = os.environ.get(environ_name)
      if value is not None:
        self.__headers.setdefault(header_name, value)

    self.__headers.setdefault('X-AppEngine-Current-Namespace',
                              namespace_manager.get_namespace())
    if query and params:
      raise InvalidTaskError('Query string and parameters both present; '
                             'only one of these may be supplied')

    if self.__method == 'PULL':
      if not self.__default_url:
        raise InvalidTaskError('url must not be specified for PULL task')
      if kwargs.get('headers'):
        raise InvalidTaskError('headers must not be specified for PULL task')
      if params:
        if payload:
          raise InvalidTaskError(
              'Message body and parameters both present for '
              'POST method; only one of these may be supplied')
        payload = Task.__encode_params(params)
      if payload is None:
        raise InvalidTaskError('payload must be specified for PULL task')
      self.__payload = Task.__convert_payload(payload, self.__headers)
    elif self.__method == 'POST':
      if payload and params:
        raise InvalidTaskError('Message body and parameters both present for '
                               'POST method; only one of these may be supplied')
      elif query:
        raise InvalidTaskError('POST method may not have a query string; '
                               'use the "params" keyword argument instead')
      elif params:
        self.__payload = Task.__encode_params(params)
        self.__headers.setdefault(
            'content-type', 'application/x-www-form-urlencoded')
      elif payload is not None:
        self.__payload = Task.__convert_payload(payload, self.__headers)
    elif self.__method in _NON_POST_HTTP_METHODS:
      if payload and self.__method not in _BODY_METHODS:
        raise InvalidTaskError('Payload may only be specified for methods %s' %
                               ', '.join(_BODY_METHODS))
      if payload:
        self.__payload = Task.__convert_payload(payload, self.__headers)
      if params:
        query = Task.__encode_params(params)
      if query:
        self.__relative_url = '%s?%s' % (self.__relative_url, query)
    else:
      raise InvalidTaskError('Invalid method: %s' % self.__method)

    host_suffix = '.%s' % os.environ.get('DEFAULT_VERSION_HOSTNAME', '')
    self.__target = kwargs.get('target')
    if self.__target is not None and 'Host' in self.__headers:
      raise InvalidTaskError(
          'A host header may not set when a target is specified.')
    elif self.__target is not None:
      self.__headers['Host'] = '%s%s' % (
          self.__target, host_suffix)
    elif 'Host' in self.__headers:
      host = self.__headers['Host']
      if host.endswith(host_suffix):
        self.__target = host[:-len(host_suffix)]
    elif 'HTTP_HOST' in os.environ:

      self.__headers['Host'] = os.environ['HTTP_HOST']

    self.__headers_list = _flatten_params(self.__headers)
    self.__eta_posix = Task.__determine_eta_posix(
        kwargs.get('eta'), kwargs.get('countdown'))
    self.__eta = None
    self.__retry_options = kwargs.get('retry_options')
    self.__enqueued = False
    self.__deleted = False

    if size_check:
      if self.__method == 'PULL':
        max_task_size_bytes = MAX_PULL_TASK_SIZE_BYTES
      else:
        max_task_size_bytes = MAX_PUSH_TASK_SIZE_BYTES
      if self.size > max_task_size_bytes:
        raise TaskTooLargeError('Task size must be less than %d; found %d' %
                                (max_task_size_bytes, self.size))

  @staticmethod
  def __determine_url(relative_url):
    """Determines the URL of a task given a relative URL and a name.

    Args:
      relative_url: The relative URL for the Task.

    Returns:
      Tuple (default_url, relative_url, query) where:
        default_url: True if this Task is using the default URL scheme;
          False otherwise.
        relative_url: String containing the relative URL for this Task.
        query: The query string for this task.

    Raises:
      InvalidUrlError if the relative_url is invalid.
    """
    if not relative_url:
      default_url, query = True, ''
    else:
      default_url = False
      try:
        relative_url, query = _parse_relative_url(relative_url)
      except _RelativeUrlError, e:
        raise InvalidUrlError(e)

    if len(relative_url) > MAX_URL_LENGTH:
      raise InvalidUrlError(
          'Task URL must be less than %d characters; found %d' %
          (MAX_URL_LENGTH, len(relative_url)))

    return (default_url, relative_url, query)

  @staticmethod
  def __determine_eta_posix(eta=None, countdown=None, current_time=time.time):
    """Determines the ETA for a task.

    If 'eta' and 'countdown' are both None, the current time will be used.
    Otherwise, only one of them may be specified.

    Args:
      eta: A datetime.datetime specifying the absolute ETA or None;
        this may be timezone-aware or timezone-naive.
      countdown: Count in seconds into the future from the present time that
        the ETA should be assigned to.

    Returns:
      A float giving a POSIX timestamp containing the ETA.

    Raises:
      InvalidTaskError if the parameters are invalid.
    """
    if eta is not None and countdown is not None:
      raise InvalidTaskError('May not use a countdown and ETA together')
    elif eta is not None:
      if not isinstance(eta, datetime.datetime):
        raise InvalidTaskError('ETA must be a datetime.datetime instance')
      elif eta.tzinfo is None:

        return time.mktime(eta.timetuple()) + eta.microsecond*1e-6
      else:

        return calendar.timegm(eta.utctimetuple()) + eta.microsecond*1e-6
    elif countdown is not None:
      try:
        countdown = float(countdown)
      except ValueError:
        raise InvalidTaskError('Countdown must be a number')
      except OverflowError:
        raise InvalidTaskError('Countdown out of range')
      else:
        return current_time() + countdown
    else:
      return current_time()

  @staticmethod
  def __encode_params(params):
    """URL-encodes a list of parameters.

    Args:
      params: Dictionary of parameters, possibly with iterable values.

    Returns:
      URL-encoded version of the params, ready to be added to a query string or
      POST body.
    """
    return urllib.urlencode(_flatten_params(params))

  @staticmethod
  def __convert_payload(payload, headers):
    """Converts a Task payload into UTF-8 and sets headers if necessary.

    Args:
      payload: The payload data to convert.
      headers: Dictionary of headers.

    Returns:
      The payload as a non-unicode string.

    Raises:
      InvalidTaskError if the payload is not a string or unicode instance.
    """
    if isinstance(payload, unicode):
      headers.setdefault('content-type', 'text/plain; charset=utf-8')
      payload = payload.encode('utf-8')
    elif not isinstance(payload, str):
      raise InvalidTaskError(
          'Task payloads must be strings; invalid payload: %r' % payload)
    return payload

  @property
  def on_queue_url(self):
    """Returns True if this Task will run on the queue's URL."""
    return self.__default_url

  @property
  def eta_posix(self):
    """Returns a POSIX timestamp giving when this Task will execute."""
    if self.__eta_posix is None and self.__eta is not None:

      self.__eta_posix = Task.__determine_eta_posix(self.__eta)
    return self.__eta_posix

  @property
  def eta(self):
    """Returns a datetime when this Task will execute."""
    if self.__eta is None and self.__eta_posix is not None:
      self.__eta = datetime.datetime.fromtimestamp(self.__eta_posix, _UTC)
    return self.__eta

  @property
  def headers(self):
    """Returns a copy of the headers for this Task."""
    return self.__headers.copy()

  @property
  def method(self):
    """Returns the method to use for this Task."""
    return self.__method

  @property
  def name(self):
    """Returns the name of this Task.

    Will be None if using auto-assigned Task names and this Task has not yet
    been added to a Queue.
    """
    return self.__name

  @property
  def queue_name(self):
    """Returns the name of the queue this Task is associated with.

    Will be None if this Task has not yet been added to a queue.
    """
    return self.__queue_name

  @property
  def payload(self):
    """Returns the payload for this task, which may be None."""
    return self.__payload

  @property
  def size(self):
    """Returns the size of this task in bytes."""
    HEADER_SEPERATOR = len(': \r\n')
    header_size = sum((len(key) + len(value) + HEADER_SEPERATOR)
                      for key, value in self.__headers_list)
    return (len(self.__method) + len(self.__payload or '') +
            len(self.__relative_url) + header_size)

  @property
  def url(self):
    """Returns the relative URL for this Task."""
    return self.__relative_url

  @property
  def retry_options(self):
    """Returns the TaskRetryOptions for this task, which may be None."""
    return self.__retry_options

  @property
  def retry_count(self):
    """Returns the number of retries have been done on the task."""
    return self.__retry_count

  @property
  def target(self):
    """Returns the target for this Task."""
    return self.__target

  @property
  def was_enqueued(self):
    """Returns True if this Task has been enqueued.

    Note: This will not check if this task already exists in the queue.
    """
    return self.__enqueued

  @property
  def was_deleted(self):
    """Returns True if this Task has been successfully deleted."""
    return self.__deleted

  def add(self, queue_name=_DEFAULT_QUEUE, transactional=False):
    """Adds this Task to a queue. See Queue.add."""
    return Queue(queue_name).add(self, transactional=transactional)

  def extract_params(self):
    """Returns the parameters for this task.

    Returns:
      A dictionary of strings mapping parameter names to their values as
      strings. If the same name parameter has several values then the value will
      be a list of strings. For POST and PULL requests then the parameters are
      extracted from the task payload. For all other methods, the parameters are
      extracted from the url query string. An empty dictionary is returned if
      the task contains an empty payload or query string.

    Raises:
      ValueError: if the payload does not contain valid
        'application/x-www-form-urlencoded' data (for POST and PULL) or the url
        does not contain a valid query (all other methods).
    """
    if self.__method in ('PULL', 'POST'):

      query = self.__payload
    else:
      query = urlparse.urlparse(self.__relative_url).query

    p = {}
    if not query:
      return p

    for key, value in cgi.parse_qsl(
        query, keep_blank_values=True, strict_parsing=True):
      p.setdefault(key, []).append(value)

    for key, value in p.items():
      if len(value) == 1:
        p[key] = value[0]

    return p


class Queue(object):
  """Represents a Queue."""

  def __init__(self, name=_DEFAULT_QUEUE):
    """Initializer.

    Args:
      name: Name of this queue. If not supplied, defaults to the default queue.

    Raises:
      InvalidQueueNameError if the queue name is invalid.
    """


    if not _QUEUE_NAME_RE.match(name):
      raise InvalidQueueNameError(
          'Queue name does not match pattern "%s"; found %s' %
          (_QUEUE_NAME_PATTERN, name))
    self.__name = name
    self.__url = '%s/%s' % (_DEFAULT_QUEUE_PATH, self.__name)


    self._app = None

  def purge(self):
    """Removes all the tasks in this Queue.

    This function takes constant time to purge a Queue and some delay may apply
    before the call is effective.

    Raises:
      Error-subclass on application errors.
    """
    request = taskqueue_service_pb.TaskQueuePurgeQueueRequest()
    response = taskqueue_service_pb.TaskQueuePurgeQueueResponse()

    request.set_queue_name(self.__name)
    if self._app:
      request.set_app_id(self._app)

    try:
      apiproxy_stub_map.MakeSyncCall('taskqueue',
                                     'PurgeQueue',
                                     request,
                                     response)
    except apiproxy_errors.ApplicationError, e:
      raise self.__TranslateError(e.application_error, e.error_detail)

  def delete_tasks(self, task):
    """Deletes a Task or list of Tasks in this Queue.

    When multiple tasks are specified, an exception will be raised if any
    individual task fails to be deleted. Check the task.was_deleted property.

    Task name is the only task attribute used to select tasks for deletion. If
    there is any task with was_deleted property set to True, or without a task
    name, a BadTaskStateError will be raised immediately.

    Args:
      task: A Task instance or a list of Task instances that will be deleted
        from the Queue.

    Returns:
      The Task or list of tasks passed into this call.

    Raises:
      BadTaskStateError: if the Task(s) to be deleted do not have task names or
        have already been deleted.
      Error-subclass on application errors.
    """
    try:
      tasks = list(iter(task))
    except TypeError:
      tasks = [task]
      multiple = False
    else:
      multiple = True

    self.__DeleteTasks(tasks)

    if multiple:
      return tasks
    else:
      assert len(tasks) == 1
      return tasks[0]

  def __DeleteTasks(self, tasks):
    """Internal implementation of .delete() where tasks must be a list."""

    request = taskqueue_service_pb.TaskQueueDeleteRequest()
    response = taskqueue_service_pb.TaskQueueDeleteResponse()

    request.set_queue_name(self.__name)
    task_names = set()
    for task in tasks:
      if not task.name:
        raise BadTaskStateError('Task name must be specified for a task')
      if task.was_deleted:
        raise BadTaskStateError('Task %s has already been deleted' % task.name)
      if task.name in task_names:
        raise DuplicateTaskNameError(
            'The task name %r is used more than once in the request' %
            task.name)
      task_names.add(task.name)
      request.add_task_name(task.name)

    try:
      apiproxy_stub_map.MakeSyncCall('taskqueue', 'Delete', request, response)
    except apiproxy_errors.ApplicationError, e:
      raise self.__TranslateError(e.application_error, e.error_detail)

    assert response.result_size() == len(tasks), (
        'expected %d results from detele(), got %d' % (
            len(tasks), response.result_size()))

    exception = None
    for task, result in zip(tasks, response.result_list()):
      if result == taskqueue_service_pb.TaskQueueServiceError.OK:
        task._Task__deleted = True
      elif (
          result == taskqueue_service_pb.TaskQueueServiceError.UNKNOWN_TASK or
          result == taskqueue_service_pb.TaskQueueServiceError.TOMBSTONED_TASK):
        task._Task__deleted = False
      elif exception is None:
        exception = self.__TranslateError(result)

    if exception is not None:
      raise exception

    return tasks

  def lease_tasks(self, lease_seconds, max_tasks):
    """Leases a number of tasks from the Queue for a period of time.

    This method can only be performed on a pull Queue. Any non-pull tasks in
    the pull Queue will be converted into pull tasks when being leased. If
    fewer than max_tasks are available, all available tasks will be returned.
    The lease_tasks method supports leasing at most 1000 tasks for no longer
    than a week in a single call.

    Args:
      lease_seconds: Number of seconds to lease the tasks.
      max_tasks: Max number of tasks to lease from the pull Queue.

    Returns:
      A list of tasks leased from the Queue.

    Raises:
      InvalidLeaseTimeError: if lease_seconds is not a valid float or integer
        number or is outside the valid range.
      InvalidMaxTasksError: if max_tasks is not a valid integer or is outside
        the valid range.
      InvalidQueueModeError: if invoked on a queue that is not in pull mode.
      Error-subclass on application errors.
    """

    if not isinstance(lease_seconds, (float, int, long)):
      raise TypeError(
          'lease_seconds must be a float or an integer')
    lease_seconds = float(lease_seconds)

    if not isinstance(max_tasks, (int, long)):
      raise TypeError(
          'max_tasks must be an integer')

    if lease_seconds < 0.0:
      raise InvalidLeaseTimeError(
          'lease_seconds must not be negative')
    if lease_seconds > MAX_LEASE_SECONDS:
      raise InvalidLeaseTimeError(
          'Lease time must not be greater than %d seconds' %
          MAX_LEASE_SECONDS)
    if max_tasks <= 0:
      raise InvalidMaxTasksError(
          'Negative or zero tasks requested')
    if max_tasks > MAX_TASKS_PER_LEASE:
      raise InvalidMaxTasksError(
          'Only %d tasks can be leased at once' %
          MAX_TASKS_PER_LEASE)

    request = taskqueue_service_pb.TaskQueueQueryAndOwnTasksRequest()
    response = taskqueue_service_pb.TaskQueueQueryAndOwnTasksResponse()

    request.set_queue_name(self.__name)
    request.set_lease_seconds(lease_seconds)
    request.set_max_tasks(max_tasks)

    try:
      apiproxy_stub_map.MakeSyncCall('taskqueue',
                                     'QueryAndOwnTasks',
                                     request,
                                     response)
    except apiproxy_errors.ApplicationError, e:
      raise self.__TranslateError(e.application_error, e.error_detail)

    tasks = []
    for response_task in response.task_list():
      name = response_task.task_name()
      payload = response_task.body()
      task = Task(payload=payload, name=name, _size_check=False, method='PULL')


      task._Task__eta_posix = response_task.eta_usec() * 1e-6
      task._Task__retry_count = response_task.retry_count()
      task._Task__queue_name = self.__name
      tasks.append(task)

    return tasks

  def add(self, task, transactional=False):
    """Adds a Task or list of Tasks into this Queue.

    If a list of more than one Tasks is given, a raised exception does not
    guarantee that no tasks were added to the queue (unless transactional is set
    to True). To determine which tasks were successfully added when an exception
    is raised, check the Task.was_enqueued property.

    Push tasks, i.e. those with method not equal to PULL, may not be added to
    queues in pull mode. Similarly, pull tasks may not be added to queues in
    push mode.

    Args:
      task: A Task instance or a list of Task instances that will be added to
        the queue.
      transactional: If True, adds the task(s) if and only if the enclosing
        transaction is successfully committed. It is an error for transactional
        to be True in the absence of an enclosing transaction. If False, adds
        the task(s) immediately, ignoring any enclosing transaction's success or
        failure.

    Returns:
      The Task or list of tasks that was supplied to this method.

    Raises:
      BadTaskStateError: if the Task(s) has already been added to a queue.
      BadTransactionStateError: if the transactional argument is true but this
        call is being made outside of the context of a transaction.
      InvalidTaskError: if both push and pull tasks exist in the task list.
      InvalidQueueModeError: if a task with method PULL is added to a queue in
        push mode, or a task with method not equal to PULL is added to a queue
        in pull mode.
      TransactionalRequestTooLargeError: if transactional is True and the total
        size of the tasks and supporting request data exceeds
        MAX_TRANSACTIONAL_REQUEST_SIZE_BYTES.
      Error-subclass on application errors.
    """
    try:
      tasks = list(iter(task))
    except TypeError:
      tasks = [task]
      multiple = False
    else:
      multiple = True


    has_push_task = False
    has_pull_task = False
    for task in tasks:
      if task.method == 'PULL':
        has_pull_task = True
      else:
        has_push_task = True

    if has_push_task and has_pull_task:
      raise InvalidTaskError(
          'Can not add both push and pull tasks in a single call.')

    if has_push_task:
      self.__AddTasks(tasks, transactional, self.__FillAddPushTasksRequest)
    else:
      self.__AddTasks(tasks, transactional, self.__FillAddPullTasksRequest)

    if multiple:
      return tasks
    else:
      assert len(tasks) == 1
      return tasks[0]

  def __AddTasks(self, tasks, transactional, fill_request):
    """Internal implementation of adding tasks where tasks must be a list."""

    if len(tasks) > MAX_TASKS_PER_ADD:
      raise TooManyTasksError(
          'No more than %d tasks can be added in a single call' %
          MAX_TASKS_PER_ADD)

    request = taskqueue_service_pb.TaskQueueBulkAddRequest()
    response = taskqueue_service_pb.TaskQueueBulkAddResponse()

    task_names = set()
    for task in tasks:
      if task.name:
        if task.name in task_names:
          raise DuplicateTaskNameError(
              'The task name %r is used more than once in the request' %
              task.name)
        task_names.add(task.name)
      if task.was_enqueued:
        raise BadTaskStateError('Task has already been enqueued.')

      fill_request(task, request.add_add_request(), transactional)

    if transactional and (request.ByteSize() >
                          MAX_TRANSACTIONAL_REQUEST_SIZE_BYTES):
      raise TransactionalRequestTooLargeError(
          'Transactional request size must be less than %d; found %d' %
          (MAX_TRANSACTIONAL_REQUEST_SIZE_BYTES, request.ByteSize()))

    try:
      apiproxy_stub_map.MakeSyncCall('taskqueue', 'BulkAdd', request, response)
    except apiproxy_errors.ApplicationError, e:
      raise self.__TranslateError(e.application_error, e.error_detail)

    assert response.taskresult_size() == len(tasks), (
        'expected %d results from BulkAdd(), got %d' % (
        len(tasks), response.taskresult_size()))

    exception = None
    for task, task_result in zip(tasks, response.taskresult_list()):
      if task_result.result() == taskqueue_service_pb.TaskQueueServiceError.OK:
        if task_result.has_chosen_task_name():
          task._Task__name = task_result.chosen_task_name()
        task._Task__queue_name = self.__name
        task._Task__enqueued = True
      elif (task_result.result() ==
            taskqueue_service_pb.TaskQueueServiceError.SKIPPED):
        pass
      elif exception is None:
        exception = self.__TranslateError(task_result.result())

    if exception is not None:
      raise exception

    return tasks

  def __FillTaskQueueRetryParameters(self,
                                     retry_options,
                                     retry_retry_parameters):
    """Populates a TaskQueueRetryParameters with data from a TaskRetryOptions.

    Args:
      retry_options: The TaskRetryOptions instance to use as a source for the
        data to be added to retry_retry_parameters.
      retry_retry_parameters: A taskqueue_service_pb.TaskQueueRetryParameters
        to populate.
    """
    if retry_options.min_backoff_seconds is not None:
      retry_retry_parameters.set_min_backoff_sec(
          retry_options.min_backoff_seconds)

    if retry_options.max_backoff_seconds is not None:
      retry_retry_parameters.set_max_backoff_sec(
          retry_options.max_backoff_seconds)

    if retry_options.task_retry_limit is not None:
      retry_retry_parameters.set_retry_limit(retry_options.task_retry_limit)

    if retry_options.task_age_limit is not None:
      retry_retry_parameters.set_age_limit_sec(retry_options.task_age_limit)

    if retry_options.max_doublings is not None:
      retry_retry_parameters.set_max_doublings(retry_options.max_doublings)

  def __FillAddPushTasksRequest(self, task, task_request, transactional):
    """Populates a TaskQueueAddRequest with the data from a push Task instance.

    Args:
      task: The Task instance to use as a source for the data to be added to
        task_request.
      task_request: The taskqueue_service_pb.TaskQueueAddRequest to populate.
      transactional: If true then populates the task_request.transaction message
        with information from the enclosing transaction (if any).

    Raises:
      BadTaskStateError: If the task was already added to a Queue.
      BadTransactionStateError: If the transactional argument is True and there
        is no enclosing transaction.
      InvalidTaskNameError: If the transactional argument is True and the task
        is named.
    """
    task_request.set_mode(taskqueue_service_pb.TaskQueueMode.PUSH)
    self.__FillTaskCommon(task, task_request, transactional)

    adjusted_url = task.url
    if task.on_queue_url:
      adjusted_url = self.__url + task.url


    task_request.set_method(_METHOD_MAP.get(task.method))
    task_request.set_url(adjusted_url)

    if task.payload:
      task_request.set_body(task.payload)
    for key, value in _flatten_params(task.headers):
      header = task_request.add_header()
      header.set_key(key)
      header.set_value(value)

    if task.retry_options:
      self.__FillTaskQueueRetryParameters(
          task.retry_options, task_request.mutable_retry_parameters())

  def __FillAddPullTasksRequest(self, task, task_request, transactional):
    """Populates a TaskQueueAddRequest with the data from a pull Task instance.

    Args:
      task: The Task instance to use as a source for the data to be added to
        task_request.
      task_request: The taskqueue_service_pb.TaskQueueAddRequest to populate.
      transactional: If true then populates the task_request.transaction message
        with information from the enclosing transaction (if any).

    Raises:
      BadTaskStateError: if the task doesn't have a payload, or has already been
        added to a Queue.
      BadTransactionStateError: if the transactional argument is True and there
        is no enclosing transaction.
      InvalidTaskNameError: if the transactional argument is True and the task
        is named.
    """
    task_request.set_mode(taskqueue_service_pb.TaskQueueMode.PULL)
    self.__FillTaskCommon(task, task_request, transactional)
    if task.payload is not None:
      task_request.set_body(task.payload)
    else:
      raise BadTaskStateError('Pull task must have a payload')

  def __FillTaskCommon(self, task, task_request, transactional):
    """Fills common fields for both push tasks and pull tasks."""
    if self._app:
      task_request.set_app_id(self._app)
    task_request.set_queue_name(self.__name)
    task_request.set_eta_usec(long(task.eta_posix * 1e6))
    if task.name:
      task_request.set_task_name(task.name)
    else:
      task_request.set_task_name('')


    if transactional:
      from google.appengine.api import datastore
      if not datastore._MaybeSetupTransaction(task_request, []):
        raise BadTransactionStateError(
            'Transactional adds are not allowed outside of transactions')

    if task_request.has_transaction() and task.name:
      raise InvalidTaskNameError(
          'Task bound to a transaction cannot be named.')

  @property
  def name(self):
    """Returns the name of this queue."""
    return self.__name

  @staticmethod
  def __TranslateError(error, detail=''):
    """Translates a TaskQueueServiceError into an exception.

    Args:
      error: Value from TaskQueueServiceError enum.
      detail: A human-readable description of the error.

    Returns:
      The corresponding Exception sub-class for that error code.
    """
    if (error >= taskqueue_service_pb.TaskQueueServiceError.DATASTORE_ERROR
        and isinstance(error, int)):
      from google.appengine.api import datastore
      datastore_exception = datastore._DatastoreExceptionFromErrorCodeAndDetail(
          error - taskqueue_service_pb.TaskQueueServiceError.DATASTORE_ERROR,
          detail)

      class JointException(datastore_exception.__class__, DatastoreError):
        """There was a datastore error while accessing the queue."""
        __msg = (u'taskqueue.DatastoreError caused by: %s %s' %
                 (datastore_exception.__class__, detail))
        def __str__(self):
          return JointException.__msg

      return JointException()
    else:
      exception_class = _ERROR_MAPPING.get(error, None)
      if exception_class:
        return exception_class(detail)
      else:
        return Error('Application error %s: %s' % (error, detail))

  def modify_task_lease(self, task, lease_seconds):
    """Modifies the lease of a task in this queue.

    Args:
      task: A task instance that will have its lease modified.
      lease_seconds: Number of seconds, from the current time, that the task
        lease will be modified to. If lease_seconds is 0, then the task lease
        is removed and the task will be available for leasing again using
        the lease_tasks method.

    Raises:
      TypeError: if lease_seconds is not a valid float or integer.
      InvalidLeaseTimeError: if lease_seconds is outside the valid range.
      Error-subclass on application errors.
    """
    if not isinstance(lease_seconds, (float, int, long)):
      raise TypeError(
          'lease_seconds must be a float or an integer')

    lease_seconds = float(lease_seconds)

    if lease_seconds < 0.0:
      raise InvalidLeaseTimeError(
          'lease_seconds must not be negative')
    if lease_seconds > MAX_LEASE_SECONDS:
      raise InvalidLeaseTimeError(
          'lease_seconds must not be greater than %d seconds' %
          MAX_LEASE_SECONDS)

    request = taskqueue_service_pb.TaskQueueModifyTaskLeaseRequest()
    response = taskqueue_service_pb.TaskQueueModifyTaskLeaseResponse()

    request.set_queue_name(self.__name)
    request.set_task_name(task.name)
    request.set_eta_usec(int(task.eta_posix * 1e6))
    request.set_lease_seconds(lease_seconds)

    try:
      apiproxy_stub_map.MakeSyncCall('taskqueue',
                                     'ModifyTaskLease',
                                     request,
                                     response)
    except apiproxy_errors.ApplicationError, e:
      raise self.__TranslateError(e.application_error, e.error_detail)

    task._Task__eta_posix = response.updated_eta_usec() * 1e-6
    task._Task__eta = None


def add(*args, **kwargs):
  """Convenience method will create a Task and add it to a queue.

  All parameters are optional.

  Push tasks, i.e. those with method not equal to PULL, may not be added to
  queues in pull mode. Similarly, pull tasks may not be added to queues in push
  mode.

  Args:
    queue_name: Name of queue to insert task into. If not supplied, defaults to
      the default queue.
    name: Name to give the Task; if not specified, a name will be
      auto-generated when added to a queue and assigned to this object. Must
      match the _TASK_NAME_PATTERN regular expression.
    method: Method to use when accessing the webhook. Defaults to 'POST'. If
      set to 'PULL', task will not be automatiacally delivered to the webhook,
      instead it stays in the queue until leased.
    url: Relative URL where the webhook that should handle this task is
      located for this application. May have a query string unless this is
      a POST method. Must not be specified if method is PULL.
    headers: Dictionary of headers to pass to the webhook. Values in the
      dictionary may be iterable to indicate repeated header fields. Must not be
      specified if method is PULL.
    payload: The payload data for this Task that will be delivered to the
      webhook as the HTTP request body or fetched by workers for pull queues.
      This is only allowed for POST, PUT, and PULL methods.
    params: Dictionary of parameters to use for this Task. For POST and PULL
      requests these params will be encoded as
      'application/x-www-form-urlencoded' and set to the payload. For all other
      methods, the parameters will be converted to a query string. Must not be
      specified if the URL already contains a query string, or the task already
      has a payload.
    transactional: If True, adds the task(s) if and only if the enclosing
      transaction is successfully committed. It is an error for transactional
      to be True in the absence of an enclosing transaction. If False, adds
      the task(s) immediately, ignoring any enclosing transaction's success or
      failure.
    countdown: Time in seconds into the future that this Task should execute.
      Defaults to zero.
    eta: A datetime.datetime specifying the absolute time at which the task
      should be executed. Must not be specified if 'countdown' is specified.
      This may be timezone-aware or timezone-naive. If None, defaults to now.
      For pull tasks, no worker will be able to lease this task before the time
      indicated by eta.
    retry_options: TaskRetryOptions used to control when the task will be
      retried if it fails.

  Returns:
    The Task that was added to the queue.

  Raises:
    InvalidTaskError if any of the parameters are invalid;
    InvalidTaskNameError if the task name is invalid;
    InvalidUrlError if the task URL is invalid or too long;
    TaskTooLargeError if the task with its payload is too large.
    InvalidQueueModeError if a task with method PULL is added to a queue in push
      mode, or a task with method not equal to PULL is added to a queue in pull
      mode.
    TransactionalRequestTooLargeError: if transactional is True and the total
      size of the tasks and supporting request data exceeds
      MAX_TRANSACTIONAL_REQUEST_SIZE_BYTES.
  """
  transactional = kwargs.pop('transactional', False)
  queue_name = kwargs.pop('queue_name', _DEFAULT_QUEUE)
  return Task(*args, **kwargs).add(
      queue_name=queue_name, transactional=transactional)