/*

 * Copyright 2020, 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 NIOCore

import NIOHPACK

/// A container for RPC response parts.

internal struct ResponsePartContainer<Response> {

  /// The type of handler for response message part.

  enum ResponseHandler {

    case unary(EventLoopPromise<Response>)

    case stream((Response) -> Void)

  }

  var lazyInitialMetadataPromise: LazyEventLoopPromise<HPACKHeaders>

  /// A handler for response messages.

  let responseHandler: ResponseHandler

  /// A promise for the trailing metadata.

  var lazyTrailingMetadataPromise: LazyEventLoopPromise<HPACKHeaders>

  /// A promise for the call status.

  var lazyStatusPromise: LazyEventLoopPromise<GRPCStatus>

  /// Fail all promises - except for the status promise - with the given error status. Succeed the

  /// status promise.

  mutating func fail(with error: Error, status: GRPCStatus) {

    self.lazyInitialMetadataPromise.fail(error)

    switch self.responseHandler {

    case let .unary(response):

      response.fail(error)

    case .stream:

      ()

    }

    self.lazyTrailingMetadataPromise.fail(error)

    // We always succeed the status.

    self.lazyStatusPromise.succeed(status)

  }

  /// Make a response container for a unary response.

  init(eventLoop: EventLoop, unaryResponsePromise: EventLoopPromise<Response>) {

    self.lazyInitialMetadataPromise = eventLoop.makeLazyPromise()

    self.lazyTrailingMetadataPromise = eventLoop.makeLazyPromise()

    self.lazyStatusPromise = eventLoop.makeLazyPromise()

    self.responseHandler = .unary(unaryResponsePromise)

  }

  /// Make a response container for a response which is streamed.

  init(eventLoop: EventLoop, streamingResponseHandler: @escaping (Response) -> Void) {

    self.lazyInitialMetadataPromise = eventLoop.makeLazyPromise()

    self.lazyTrailingMetadataPromise = eventLoop.makeLazyPromise()

    self.lazyStatusPromise = eventLoop.makeLazyPromise()

    self.responseHandler = .stream(streamingResponseHandler)

  }

}