/*
 * Copyright 2019, gRPC Authors All rights reserved.
 *
 * 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.
 */
import Logging
import NIO
import NIOHPACK
import NIOHTTP2

/// A server-streaming gRPC call. The request is sent on initialization, each response is passed to
/// the provided observer block.
public final class ServerStreamingCall<RequestPayload, ResponsePayload>: ClientCall {
  private let transport: ChannelTransport<RequestPayload, ResponsePayload>

  /// The options used to make the RPC.
  public let options: CallOptions

  /// The `Channel` used to transport messages for this RPC.
  public var subchannel: EventLoopFuture<Channel> {
    return self.transport.streamChannel()
  }

  /// The `EventLoop` this call is running on.
  public var eventLoop: EventLoop {
    return self.transport.eventLoop
  }

  /// Cancel this RPC if it hasn't already completed.
  public func cancel(promise: EventLoopPromise<Void>?) {
    self.transport.cancel(promise: promise)
  }

  // MARK: - Response Parts

  /// The initial metadata returned from the server.
  public var initialMetadata: EventLoopFuture<HPACKHeaders> {
    if self.eventLoop.inEventLoop {
      return self.transport.responseContainer.lazyInitialMetadataPromise.getFutureResult()
    } else {
      return self.eventLoop.flatSubmit {
        return self.transport.responseContainer.lazyInitialMetadataPromise.getFutureResult()
      }
    }
  }

  /// The trailing metadata returned from the server.
  public var trailingMetadata: EventLoopFuture<HPACKHeaders> {
    if self.eventLoop.inEventLoop {
      return self.transport.responseContainer.lazyTrailingMetadataPromise.getFutureResult()
    } else {
      return self.eventLoop.flatSubmit {
        return self.transport.responseContainer.lazyTrailingMetadataPromise.getFutureResult()
      }
    }
  }

  /// The final status of the the RPC.
  public var status: EventLoopFuture<GRPCStatus> {
    if self.eventLoop.inEventLoop {
      return self.transport.responseContainer.lazyStatusPromise.getFutureResult()
    } else {
      return self.eventLoop.flatSubmit {
        return self.transport.responseContainer.lazyStatusPromise.getFutureResult()
      }
    }
  }

  internal init(
    transport: ChannelTransport<RequestPayload, ResponsePayload>,
    options: CallOptions
  ) {
    self.transport = transport
    self.options = options
  }

  internal func send(_ head: _GRPCRequestHead, request: RequestPayload) {
    self.transport.sendUnary(
      head,
      request: request,
      compressed: self.options.messageEncoding.enabledForRequests
    )
  }
}

extension ServerStreamingCall {
  internal static func makeOnHTTP2Stream<
    Serializer: MessageSerializer,
    Deserializer: MessageDeserializer
  >(
    multiplexer: EventLoopFuture<HTTP2StreamMultiplexer>,
    serializer: Serializer,
    deserializer: Deserializer,
    callOptions: CallOptions,
    errorDelegate: ClientErrorDelegate?,
    logger: Logger,
    responseHandler: @escaping (ResponsePayload) -> Void
  ) -> ServerStreamingCall<RequestPayload, ResponsePayload>
    where Serializer.Input == RequestPayload,
    Deserializer.Output == ResponsePayload {
    let eventLoop = multiplexer.eventLoop
    let transport = ChannelTransport<RequestPayload, ResponsePayload>(
      multiplexer: multiplexer,
      serializer: serializer,
      deserializer: deserializer,
      responseContainer: .init(eventLoop: eventLoop, streamingResponseHandler: responseHandler),
      callType: .serverStreaming,
      timeLimit: callOptions.timeLimit,
      errorDelegate: errorDelegate,
      logger: logger
    )

    return ServerStreamingCall(transport: transport, options: callOptions)
  }

  internal static func make<Serializer: MessageSerializer, Deserializer: MessageDeserializer>(
    serializer: Serializer,
    deserializer: Deserializer,
    fakeResponse: FakeStreamingResponse<RequestPayload, ResponsePayload>?,
    callOptions: CallOptions,
    logger: Logger,
    responseHandler: @escaping (ResponsePayload) -> Void
  ) -> ServerStreamingCall<RequestPayload, ResponsePayload>
    where Serializer.Input == RequestPayload,
    Deserializer.Output == ResponsePayload {
    let eventLoop = fakeResponse?.channel.eventLoop ?? EmbeddedEventLoop()
    let responseContainer = ResponsePartContainer(
      eventLoop: eventLoop,
      streamingResponseHandler: responseHandler
    )

    let transport: ChannelTransport<RequestPayload, ResponsePayload>
    if let callProxy = fakeResponse {
      transport = .init(
        fakeResponse: callProxy,
        responseContainer: responseContainer,
        timeLimit: callOptions.timeLimit,
        logger: logger
      )

      callProxy.activate()
    } else {
      transport = .makeTransportForMissingFakeResponse(
        eventLoop: eventLoop,
        responseContainer: responseContainer,
        logger: logger
      )
    }

    return ServerStreamingCall(transport: transport, options: callOptions)
  }
}