/*
    * Copyright 2016 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.example.http2.helloworld.frame.server;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.ByteBufUtil;
  import io.netty.channel.ChannelDuplexHandler;
  import io.netty.channel.ChannelHandler.Sharable;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.handler.codec.http2.DefaultHttp2DataFrame;
  import io.netty.handler.codec.http2.DefaultHttp2Headers;
  import io.netty.handler.codec.http2.DefaultHttp2HeadersFrame;
  import io.netty.handler.codec.http2.DefaultHttp2WindowUpdateFrame;
  import io.netty.handler.codec.http2.Http2DataFrame;
  import io.netty.handler.codec.http2.Http2FrameStream;
  import io.netty.handler.codec.http2.Http2Headers;
  import io.netty.handler.codec.http2.Http2HeadersFrame;
  import io.netty.util.CharsetUtil;
  
  import static io.netty.buffer.Unpooled.copiedBuffer;
  import static io.netty.buffer.Unpooled.unreleasableBuffer;
  import static io.netty.handler.codec.http.HttpResponseStatus.OK;
  
  /**
   * A simple handler that responds with the message "Hello World!" using "frame codec" http2 API.
   */
  @Sharable
  public class HelloWorldHttp2Handler extends ChannelDuplexHandler {
  
      static final ByteBuf RESPONSE_BYTES = unreleasableBuffer(
              copiedBuffer("Hello World", CharsetUtil.UTF_8)).asReadOnly();
  
      @Override
      public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
          super.exceptionCaught(ctx, cause);
          cause.printStackTrace();
          ctx.close();
      }
  
      @Override
      public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
          if (msg instanceof Http2HeadersFrame) {
              onHeadersRead(ctx, (Http2HeadersFrame) msg);
          } else if (msg instanceof Http2DataFrame) {
              onDataRead(ctx, (Http2DataFrame) msg);
          } else {
              super.channelRead(ctx, msg);
          }
      }
  
      @Override
      public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
          ctx.flush();
      }
  
      /**
       * If receive a frame with end-of-stream set, send a pre-canned response.
       */
      private static void onDataRead(ChannelHandlerContext ctx, Http2DataFrame data) throws Exception {
          Http2FrameStream stream = data.stream();
  
          if (data.isEndStream()) {
              sendResponse(ctx, stream, data.content());
          } else {
              // We do not send back the response to the remote-peer, so we need to release it.
              data.release();
          }
  
          // Update the flowcontroller
          ctx.write(new DefaultHttp2WindowUpdateFrame(data.initialFlowControlledBytes()).stream(stream));
      }
  
      /**
       * If receive a frame with end-of-stream set, send a pre-canned response.
       */
      private static void onHeadersRead(ChannelHandlerContext ctx, Http2HeadersFrame headers)
              throws Exception {
          if (headers.isEndStream()) {
              ByteBuf content = ctx.alloc().buffer();
              content.writeBytes(RESPONSE_BYTES.duplicate());
              ByteBufUtil.writeAscii(content, " - via HTTP/2");
              sendResponse(ctx, headers.stream(), content);
          }
      }
  
      /**
      * Sends a "Hello World" DATA frame to the client.
      */
     private static void sendResponse(ChannelHandlerContext ctx, Http2FrameStream stream, ByteBuf payload) {
         // Send a frame for the response status
         Http2Headers headers = new DefaultHttp2Headers().status(OK.codeAsText());
         ctx.write(new DefaultHttp2HeadersFrame(headers).stream(stream));
         ctx.write(new DefaultHttp2DataFrame(payload, true).stream(stream));
     }
 }