# Copyright 2025 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 typing import List, Optional, Tuple
from google.cloud import _storage_v2
from google.cloud.storage.asyncio.async_grpc_client import AsyncGrpcClient
from google.cloud.storage.asyncio.async_abstract_object_stream import (
    _AsyncAbstractObjectStream,
)

from google.api_core.bidi_async import AsyncBidiRpc


class _AsyncReadObjectStream(_AsyncAbstractObjectStream):
    """Class representing a gRPC bidi-stream for reading data from a GCS ``Object``.

    This class provides a unix socket-like interface to a GCS ``Object``, with
    methods like ``open``, ``close``, ``send``, and ``recv``.

    :type client: :class:`~google.cloud.storage.asyncio.async_grpc_client.AsyncGrpcClient.grpc_client`
    :param client: async grpc client to use for making API requests.

    :type bucket_name: str
    :param bucket_name: The name of the GCS ``bucket`` containing the object.

    :type object_name: str
    :param object_name: The name of the GCS ``object`` to be read.

    :type generation_number: int
    :param generation_number: (Optional) If present, selects a specific revision of
                              this object.

    :type read_handle: _storage_v2.BidiReadHandle
    :param read_handle: (Optional) An existing handle for reading the object.
                        If provided, opening the bidi-gRPC connection will be faster.
    """

    def __init__(
        self,
        client: AsyncGrpcClient.grpc_client,
        bucket_name: str,
        object_name: str,
        generation_number: Optional[int] = None,
        read_handle: Optional[_storage_v2.BidiReadHandle] = None,
    ) -> None:
        if client is None:
            raise ValueError("client must be provided")
        if bucket_name is None:
            raise ValueError("bucket_name must be provided")
        if object_name is None:
            raise ValueError("object_name must be provided")

        super().__init__(
            bucket_name=bucket_name,
            object_name=object_name,
            generation_number=generation_number,
        )
        self.client: AsyncGrpcClient.grpc_client = client
        self.read_handle: Optional[_storage_v2.BidiReadHandle] = read_handle

        self._full_bucket_name = f"projects/_/buckets/{self.bucket_name}"

        self.rpc = self.client._client._transport._wrapped_methods[
            self.client._client._transport.bidi_read_object
        ]
        self.metadata = (("x-goog-request-params", f"bucket={self._full_bucket_name}"),)
        self.socket_like_rpc: Optional[AsyncBidiRpc] = None
        self._is_stream_open: bool = False
        self.persisted_size: Optional[int] = None

    async def open(self, metadata: Optional[List[Tuple[str, str]]] = None) -> None:
        """Opens the bidi-gRPC connection to read from the object.

        This method sends an initial request to start the stream and receives
        the first response containing metadata and a read handle.

        Args:
            metadata (Optional[List[Tuple[str, str]]]): Additional metadata
                to send with the initial stream request, e.g., for routing tokens.
        """
        if self._is_stream_open:
            raise ValueError("Stream is already open")

        read_handle = self.read_handle if self.read_handle else None

        read_object_spec = _storage_v2.BidiReadObjectSpec(
            bucket=self._full_bucket_name,
            object=self.object_name,
            generation=self.generation_number if self.generation_number else None,
            read_handle=read_handle,
        )
        self.first_bidi_read_req = _storage_v2.BidiReadObjectRequest(
            read_object_spec=read_object_spec
        )

        # Build the x-goog-request-params header
        request_params = [f"bucket={self._full_bucket_name}"]
        other_metadata = []
        if metadata:
            for key, value in metadata:
                if key == "x-goog-request-params":
                    request_params.append(value)
                else:
                    other_metadata.append((key, value))

        current_metadata = other_metadata
        current_metadata.append(("x-goog-request-params", "&".join(request_params)))

        self.socket_like_rpc = AsyncBidiRpc(
            self.rpc,
            initial_request=self.first_bidi_read_req,
            metadata=current_metadata,
        )
        await self.socket_like_rpc.open()  # this is actually 1 send
        response = await self.socket_like_rpc.recv()
        # populated only in the first response of bidi-stream and when opened
        # without using `read_handle`
        if hasattr(response, "metadata") and response.metadata:
            if self.generation_number is None:
                self.generation_number = response.metadata.generation
            # update persisted size
            self.persisted_size = response.metadata.size

        if response and response.read_handle:
            self.read_handle = response.read_handle

        self._is_stream_open = True

    async def close(self) -> None:
        """Closes the bidi-gRPC connection."""
        if not self._is_stream_open:
            raise ValueError("Stream is not open")
        await self.requests_done()
        await self.socket_like_rpc.close()
        self._is_stream_open = False

    async def requests_done(self):
        """Signals that all requests have been sent."""

        await self.socket_like_rpc.send(None)
        await self.socket_like_rpc.recv()

    async def send(
        self, bidi_read_object_request: _storage_v2.BidiReadObjectRequest
    ) -> None:
        """Sends a request message on the stream.

        Args:
            bidi_read_object_request (:class:`~google.cloud._storage_v2.types.BidiReadObjectRequest`):
                The request message to send. This is typically used to specify
                the read offset and limit.
        """
        if not self._is_stream_open:
            raise ValueError("Stream is not open")
        await self.socket_like_rpc.send(bidi_read_object_request)

    async def recv(self) -> _storage_v2.BidiReadObjectResponse:
        """Receives a response from the stream.

        This method waits for the next message from the server, which could
        contain object data or metadata.

        Returns:
            :class:`~google.cloud._storage_v2.types.BidiReadObjectResponse`:
                The response message from the server.
        """
        if not self._is_stream_open:
            raise ValueError("Stream is not open")
        response = await self.socket_like_rpc.recv()
        # Update read_handle if present in response
        if response and response.read_handle:
            self.read_handle = response.read_handle
        return response

    @property
    def is_stream_open(self) -> bool:
        return self._is_stream_open
