# Copyright 2020 Google LLC
#
# 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.

from abc import abstractmethod, ABCMeta
from typing import (
    ContextManager,
    Union,
    AsyncContextManager,
    AsyncIterator,
    Callable,
    Optional,
    Set,
)

from google.cloud.pubsub_v1.subscriber.futures import StreamingPullFuture
from google.cloud.pubsub_v1.subscriber.message import Message

from google.cloud.pubsublite.types import (
    SubscriptionPath,
    FlowControlSettings,
    Partition,
)


class AsyncSubscriberClientInterface(AsyncContextManager, metaclass=ABCMeta):
    """
    An AsyncSubscriberClientInterface reads messages similar to Google Pub/Sub, but must be used in an
    async context.
    Any subscribe failures are unlikely to succeed if retried.

    Must be used in an `async with` block or have __aenter__() awaited before use.
    """

    @abstractmethod
    async def subscribe(
        self,
        subscription: Union[SubscriptionPath, str],
        per_partition_flow_control_settings: FlowControlSettings,
        fixed_partitions: Optional[Set[Partition]] = None,
    ) -> AsyncIterator[Message]:
        """
        Read messages from a subscription.

        Args:
          subscription: The subscription to subscribe to.
          per_partition_flow_control_settings: The flow control settings for each partition subscribed to. Note that these
              settings apply to each partition individually, not in aggregate.
          fixed_partitions: A fixed set of partitions to subscribe to. If not present, will instead use auto-assignment.

        Returns:
          An AsyncIterator with Messages that must have ack() called on each exactly once.

        Raises:
          GoogleApiCallError: On a permanent failure.
        """
        raise NotImplementedError()


MessageCallback = Callable[[Message], None]


class SubscriberClientInterface(ContextManager, metaclass=ABCMeta):
    """
    A SubscriberClientInterface reads messages similar to Google Pub/Sub.
    Any subscribe failures are unlikely to succeed if retried.

    Must be used in a `with` block or have __enter__() called before use.
    """

    @abstractmethod
    def subscribe(
        self,
        subscription: Union[SubscriptionPath, str],
        callback: MessageCallback,
        per_partition_flow_control_settings: FlowControlSettings,
        fixed_partitions: Optional[Set[Partition]] = None,
    ) -> StreamingPullFuture:
        """
        This method starts a background thread to begin pulling messages from
        a Pub/Sub Lite subscription and scheduling them to be processed using the
        provided ``callback``.

        Args:
          subscription: The subscription to subscribe to.
          callback: The callback function. This function receives the message as its only argument.
          per_partition_flow_control_settings: The flow control settings for each partition subscribed to. Note that these
              settings apply to each partition individually, not in aggregate.
          fixed_partitions: A fixed set of partitions to subscribe to. If not present, will instead use auto-assignment.

        Returns:
          A StreamingPullFuture instance that can be used to manage the background stream.

        Raises:
          GoogleApiCallError: On a permanent failure.
        """
        raise NotImplementedError()