/*

 * 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

/// A handler which redirects all writes into a callback until the `.end` part is seen, after which

/// all writes will be failed.

///

/// This handler is intended for use with 'fake' response streams the 'FakeChannel'.

internal final class WriteCapturingHandler<Request>: ChannelOutboundHandler {

  typealias OutboundIn = _GRPCClientRequestPart<Request>

  typealias RequestHandler = (FakeRequestPart<Request>) -> Void

  private var state: State

  private enum State {

    case active(RequestHandler)

    case inactive

  }

  internal init(requestHandler: @escaping RequestHandler) {

    self.state = .active(requestHandler)

  }

  internal func write(

    context: ChannelHandlerContext,

    data: NIOAny,

    promise: EventLoopPromise<Void>?

  ) {

    guard case let .active(handler) = self.state else {

      promise?.fail(ChannelError.ioOnClosedChannel)

      return

    }

    switch self.unwrapOutboundIn(data) {

    case let .head(requestHead):

      handler(.metadata(requestHead.customMetadata))

    case let .message(messageContext):

      handler(.message(messageContext.message))

    case .end:

      handler(.end)

      // We're done now.

      self.state = .inactive

    }

    promise?.succeed(())

  }

}