# Copyright 2020 The Chromium Authors
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
"""A helper module for interfacing with google cloud tasks.

This module wraps Gooogle Cloud Tasks, link to its documentation:
https://googleapis.dev/python/cloudtasks/1.3.0/gapic/v2/api.html
"""

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

import logging
import six
from six.moves import urllib

from google.api_core import exceptions
from google.api_core import retry

import settings

if not settings.unit_test_mode:
  import grpc
  from google.cloud import tasks_v2
  from google.cloud.tasks_v2.services import cloud_tasks

_client = None
# Default exponential backoff retry config for enqueueing, not to be confused
# with retry config for dispatching, which exists per queue.
_DEFAULT_RETRY = retry.Retry(initial=.1, maximum=1.6, multiplier=2, deadline=10)


def _get_client():
  # type: () -> tasks.CloudTasksClient
  """Returns a cloud tasks client."""
  global _client
  if not _client:
    if settings.local_mode:
      transport = cloud_tasks.transports.CloudTasksGrpcTransport(
          channel=grpc.insecure_channel(settings.CLOUD_TASKS_EMULATOR_ADDRESS))
      _client = tasks_v2.CloudTasksClient(transport=transport)
    else:
      _client = tasks_v2.CloudTasksClient()
  return _client


def create_task(task, queue='default', **kwargs):
  # type: (Union[dict, tasks.types.Task], str, **Any) ->
  #     tasks.types.Task
  """Tries and catches creating a cloud task.

  This exposes a simplied task creation interface by wrapping
  tasks.CloudTasksClient.create_task; see its documentation:
  https://googleapis.dev/python/cloudtasks/1.5.0/gapic/v2/api.html#google.cloud.tasks_v2.CloudTasksClient.create_task

  Args:
    task: A dict or Task describing the task to add.
    queue: A string indicating name of the queue to add task to.
    kwargs: Additional arguments to pass to cloud task client's create_task

  Returns:
    Successfully created Task object.

  Raises:
    AttributeError: If input task is malformed or missing attributes.
    google.api_core.exceptions.GoogleAPICallError: If the request failed for any
        reason.
    google.api_core.exceptions.RetryError: If the request failed due to a
        retryable error and retry attempts failed.
    ValueError: If the parameters are invalid.
  """
  client = _get_client()

  parent = client.queue_path(
      settings.app_id, settings.CLOUD_TASKS_REGION, queue)
  target = task.get('app_engine_http_request').get('relative_uri')
  kwargs.setdefault('retry', _DEFAULT_RETRY)
  logging.info('Enqueueing %s task to %s', target, parent)
  return client.create_task(parent=parent, task=task, **kwargs)


def generate_simple_task(url, params):
  # type: (str, dict) -> dict
  """Construct a basic cloud tasks Task for an appengine handler.
  Args:
    url: Url path that handles the task.
    params: Url query parameters dict.

  Returns:
    Dict representing a cloud tasks Task object.
  """
  return {
      'app_engine_http_request':
          {
              'relative_uri': url,
              'body': six.ensure_binary(urllib.parse.urlencode(params)),
              'headers': {
                  'Content-type': 'application/x-www-form-urlencoded'
              }
          }
  }