/*
    * ====================================================================
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF 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
   *
   *   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.
   * ====================================================================
   *
   * This software consists of voluntary contributions made by many
   * individuals on behalf of the Apache Software Foundation.  For more
   * information on the Apache Software Foundation, please see
   * <http://www.apache.org/>.
   *
   */
  package org.apache.hc.core5.reactive;
  
  import java.io.IOException;
  import java.nio.ByteBuffer;
  import java.util.List;
  import java.util.concurrent.atomic.AtomicReference;
  
  import org.apache.hc.core5.function.Callback;
  import org.apache.hc.core5.http.EntityDetails;
  import org.apache.hc.core5.http.Header;
  import org.apache.hc.core5.http.HttpException;
  import org.apache.hc.core5.http.HttpRequest;
  import org.apache.hc.core5.http.nio.AsyncServerExchangeHandler;
  import org.apache.hc.core5.http.nio.CapacityChannel;
  import org.apache.hc.core5.http.nio.DataStreamChannel;
  import org.apache.hc.core5.http.nio.ResponseChannel;
  import org.apache.hc.core5.http.protocol.HttpContext;
  import org.reactivestreams.Publisher;
  
  /**
   * An implementation of {@link AsyncServerExchangeHandler} designed to work with reactive streams.
   *
   * @since 5.0
   */
  public final class ReactiveServerExchangeHandler implements AsyncServerExchangeHandler {
  
      private final ReactiveRequestProcessor requestProcessor;
      private final AtomicReference<ReactiveDataProducer> responseProducer = new AtomicReference<>();
      private final ReactiveDataConsumer requestConsumer;
      private volatile DataStreamChannel channel;
  
      /**
       * Creates a {@code ReactiveServerExchangeHandler}.
       *
       * @param requestProcessor the {@link ReactiveRequestProcessor} instance to
       *                         invoke when the request is ready to be handled.
       */
      public ReactiveServerExchangeHandler(final ReactiveRequestProcessor requestProcessor) {
          this.requestProcessor = requestProcessor;
          this.requestConsumer = new ReactiveDataConsumer();
      }
  
      @Override
      public void handleRequest(
              final HttpRequest request,
              final EntityDetails entityDetails,
              final ResponseChannel responseChannel,
              final HttpContext context
      ) throws HttpException, IOException {
          final Callback<Publisher<ByteBuffer>> callback = result -> {
              final ReactiveDataProducer producer = new ReactiveDataProducer(result);
              if (channel != null) {
                  producer.setChannel(channel);
              }
              responseProducer.set(producer);
              result.subscribe(producer);
          };
          requestProcessor.processRequest(request, entityDetails, responseChannel, context, requestConsumer, callback);
      }
  
      @Override
      public void failed(final Exception cause) {
          requestConsumer.failed(cause);
          final ReactiveDataProducer p = responseProducer.get();
          if (p != null) {
              p.onError(cause);
          }
      }
  
      @Override
      public void updateCapacity(final CapacityChannel capacityChannel) throws IOException {
          requestConsumer.updateCapacity(capacityChannel);
      }
 
     @Override
     public void consume(final ByteBuffer src) throws IOException {
         requestConsumer.consume(src);
     }
 
     @Override
     public void streamEnd(final List<? extends Header> trailers) throws HttpException, IOException {
         requestConsumer.streamEnd(trailers);
     }
 
     @Override
     public int available() {
         final ReactiveDataProducer p = responseProducer.get();
         if (p == null) {
             return 0;
         } else {
             return p.available();
         }
     }
 
     @Override
     public void produce(final DataStreamChannel channel) throws IOException {
         this.channel = channel;
         final ReactiveDataProducer p = responseProducer.get();
         if (p != null) {
             p.produce(channel);
         }
     }
 
     @Override
     public void releaseResources() {
         final ReactiveDataProducer p = responseProducer.get();
         if (p != null) {
             p.releaseResources();
         }
         requestConsumer.releaseResources();
     }
 }