/*
    * Copyright 2021 The Netty Project
    *
    * The Netty Project licenses this file to you 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:
    *
    *   https://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.
   */
  package io.netty.handler.codec.http3;
  
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelOutboundHandlerAdapter;
  import io.netty.channel.ChannelPromise;
  import io.netty.handler.codec.http.HttpStatusClass;
  import org.jetbrains.annotations.Nullable;
  
  import static io.netty.handler.codec.http3.Http3FrameValidationUtils.frameTypeUnexpected;
  
  final class Http3RequestStreamEncodeStateValidator extends ChannelOutboundHandlerAdapter
          implements Http3RequestStreamCodecState {
      enum State {
          None,
          Headers,
          FinalHeaders,
          Trailers
      }
      private State state = State.None;
  
      @Override
      public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
          if (!(msg instanceof Http3RequestStreamFrame)) {
              super.write(ctx, msg, promise);
              return;
          }
          final Http3RequestStreamFrame frame = (Http3RequestStreamFrame) msg;
          final State nextState = evaluateFrame(state, frame);
          if (nextState == null) {
              frameTypeUnexpected(ctx, msg);
              return;
          }
          state = nextState;
          super.write(ctx, msg, promise);
      }
  
      @Override
      public boolean started() {
          return isStreamStarted(state);
      }
  
      @Override
      public boolean receivedFinalHeaders() {
          return isFinalHeadersReceived(state);
      }
  
      @Override
      public boolean terminated() {
          return isTrailersReceived(state);
      }
  
      /**
       * Evaluates the passed frame and returns the following:
       * <ul>
       *     <li>Modified {@link State} if the state should be changed.</li>
       *     <li>Same {@link State} as the passed {@code state} if no state change is necessary</li>
       *     <li>{@code null} if the frame is unexpected</li>
       * </ul>
       *
       * @param state Current state.
       * @param frame to evaluate.
       * @return Next {@link State} or {@code null} if the frame is invalid.
       */
      @Nullable
      static State evaluateFrame(State state, Http3RequestStreamFrame frame) {
          if (frame instanceof Http3PushPromiseFrame || frame instanceof Http3UnknownFrame) {
              // always allow push promise frames.
              return state;
          }
          switch (state) {
              case None:
              case Headers:
                  if (!(frame instanceof Http3HeadersFrame)) {
                      return null;
                  }
                  return isInformationalResponse((Http3HeadersFrame) frame) ? State.Headers : State.FinalHeaders;
              case FinalHeaders:
                  if (frame instanceof Http3HeadersFrame) {
                      if (isInformationalResponse((Http3HeadersFrame) frame)) {
                          // Information response after final response headers
                          return null;
                      }
                      // trailers
                      return State.Trailers;
                 }
                 return state;
             case Trailers:
                 return null;
             default:
                 throw new Error();
         }
     }
 
     static boolean isStreamStarted(State state) {
         return state != State.None;
     }
 
     static boolean isFinalHeadersReceived(State state) {
         return isStreamStarted(state) && state != State.Headers;
     }
 
     static boolean isTrailersReceived(State state) {
         return state == State.Trailers;
     }
 
     private static boolean isInformationalResponse(Http3HeadersFrame headersFrame) {
         return HttpStatusClass.valueOf(headersFrame.headers().status()) == HttpStatusClass.INFORMATIONAL;
     }
 }