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  """
  This module contains a Google PubSub sensor.
  """
  import warnings
  from typing import Any, Callable, Dict, List, Optional, Sequence, Union
  
  from google.cloud.pubsub_v1.types import ReceivedMessage
  from google.protobuf.json_format import MessageToDict
  
  from airflow.providers.google.cloud.hooks.pubsub import PubSubHook
  from airflow.sensors.base_sensor_operator import BaseSensorOperator
  from airflow.utils.decorators import apply_defaults
  
  
  class PubSubPullSensor(BaseSensorOperator):
      """Pulls messages from a PubSub subscription and passes them through XCom.
      Always waits for at least one message to be returned from the subscription.
  
      .. seealso::
          For more information on how to use this operator, take a look at the guide:
          :ref:`howto/operator:PubSubPullSensor`
  
      .. seealso::
          If you don't want to wait for at least one message to come, use Operator instead:
          :class:`~airflow.providers.google.cloud.operators.pubsub.PubSubPullOperator`
  
      This sensor operator will pull up to ``max_messages`` messages from the
      specified PubSub subscription. When the subscription returns messages,
      the poke method's criteria will be fulfilled and the messages will be
      returned from the operator and passed through XCom for downstream tasks.
  
      If ``ack_messages`` is set to True, messages will be immediately
      acknowledged before being returned, otherwise, downstream tasks will be
      responsible for acknowledging them.
  
      ``project`` and ``subscription`` are templated so you can use
      variables in them.
  
      :param project: the Google Cloud project ID for the subscription (templated)
      :type project: str
      :param subscription: the Pub/Sub subscription name. Do not include the
          full subscription path.
      :type subscription: str
      :param max_messages: The maximum number of messages to retrieve per
          PubSub pull request
      :type max_messages: int
      :param return_immediately:
          (Deprecated) This is an underlying PubSub API implementation detail.
          It has no real effect on Sensor behaviour other than some internal wait time before retrying
          on empty queue.
          The Sensor task will (by definition) always wait for a message, regardless of this argument value.
  
          If you want a non-blocking task that does not to wait for messages, please use
          :class:`~airflow.providers.google.cloud.operators.pubsub.PubSubPullOperator`
          instead.
      :type return_immediately: bool
      :param ack_messages: If True, each message will be acknowledged
          immediately rather than by any downstream tasks
      :type ack_messages: bool
      :param gcp_conn_id: The connection ID to use connecting to
          Google Cloud.
      :type gcp_conn_id: str
      :param delegate_to: The account to impersonate using domain-wide delegation of authority,
          if any. For this to work, the service account making the request must have
          domain-wide delegation enabled.
      :type delegate_to: str
      :param messages_callback: (Optional) Callback to process received messages.
          It's return value will be saved to XCom.
          If you are pulling large messages, you probably want to provide a custom callback.
          If not provided, the default implementation will convert `ReceivedMessage` objects
          into JSON-serializable dicts using `google.protobuf.json_format.MessageToDict` function.
      :type messages_callback: Optional[Callable[[List[ReceivedMessage], Dict[str, Any]], Any]]
      :param impersonation_chain: Optional service account to impersonate using short-term
          credentials, or chained list of accounts required to get the access_token
          of the last account in the list, which will be impersonated in the request.
          If set as a string, the account must grant the originating account
          the Service Account Token Creator IAM role.
          If set as a sequence, the identities from the list must grant
          Service Account Token Creator IAM role to the directly preceding identity, with first
          account from the list granting this role to the originating account (templated).
      :type impersonation_chain: Union[str, Sequence[str]]
      """
  
      template_fields = [
          'project_id',
          'subscription',
          'impersonation_chain',
      ]
      ui_color = '#ff7f50'
  
      @apply_defaults
      def __init__(
          self,
          *,
          project_id: str,
          subscription: str,
          max_messages: int = 5,
          return_immediately: bool = True,
          ack_messages: bool = False,
          gcp_conn_id: str = 'google_cloud_default',
          messages_callback: Optional[Callable[[List[ReceivedMessage], Dict[str, Any]], Any]] = None,
          delegate_to: Optional[str] = None,
          project: Optional[str] = None,
          impersonation_chain: Optional[Union[str, Sequence[str]]] = None,
          **kwargs,
      ) -> None:
          # To preserve backward compatibility
          # TODO: remove one day
          if project:
              warnings.warn(
                  "The project parameter has been deprecated. You should pass " "the project_id parameter.",
                  DeprecationWarning,
                  stacklevel=2,
              )
              project_id = project
  
          if not return_immediately:
              warnings.warn(
                  "The return_immediately parameter is deprecated.\n"
                  " It exposes what is really just an implementation detail of underlying PubSub API.\n"
                  " It has no effect on PubSubPullSensor behaviour.\n"
                  " It should be left as default value of True.\n"
                  " If is here only because of backwards compatibility.\n"
                  " If may be removed in the future.\n",
                  DeprecationWarning,
                  stacklevel=2,
              )
  
          super().__init__(**kwargs)
          self.gcp_conn_id = gcp_conn_id
          self.delegate_to = delegate_to
          self.project_id = project_id
          self.subscription = subscription
          self.max_messages = max_messages
          self.return_immediately = return_immediately
          self.ack_messages = ack_messages
          self.messages_callback = messages_callback
          self.impersonation_chain = impersonation_chain
  
          self._return_value = None
  
      def execute(self, context):
          """Overridden to allow messages to be passed"""
          super().execute(context)
          return self._return_value
  
      def poke(self, context):
          hook = PubSubHook(
              gcp_conn_id=self.gcp_conn_id,
              delegate_to=self.delegate_to,
              impersonation_chain=self.impersonation_chain,
          )
  
          pulled_messages = hook.pull(
              project_id=self.project_id,
              subscription=self.subscription,
              max_messages=self.max_messages,
              return_immediately=self.return_immediately,
          )
  
          handle_messages = self.messages_callback or self._default_message_callback
  
          self._return_value = handle_messages(pulled_messages, context)
  
          if pulled_messages and self.ack_messages:
              hook.acknowledge(
                  project_id=self.project_id,
                  subscription=self.subscription,
                  messages=pulled_messages,
              )
  
          return bool(pulled_messages)
  
      def _default_message_callback(
          self,
          pulled_messages: List[ReceivedMessage],
          context: Dict[str, Any],  # pylint: disable=unused-argument
      ):
          """
          This method can be overridden by subclasses or by `messages_callback` constructor argument.
          This default implementation converts `ReceivedMessage` objects into JSON-serializable dicts.
  
          :param pulled_messages: messages received from the topic.
          :type pulled_messages: List[ReceivedMessage]
          :param context: same as in `execute`
          :return: value to be saved to XCom.
          """
  
          messages_json = [MessageToDict(m) for m in pulled_messages]
  
          return messages_json
  