/*
    * ====================================================================
    * 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.testing.nio;
  
  import java.io.IOException;
  import java.nio.ByteBuffer;
  import java.util.List;
  import java.util.concurrent.atomic.AtomicInteger;
  
  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.HttpResponse;
  import org.apache.hc.core5.http.HttpStatus;
  import org.apache.hc.core5.http.message.BasicHttpResponse;
  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;
  
  public class EchoHandler implements AsyncServerExchangeHandler {
  
      private final static int MIN_CHUNK = 4096;
  
      private final int initBufferSize;
      private final AtomicInteger capacityIncrement;
      private volatile ByteBuffer buffer;
      private volatile CapacityChannel inputCapacityChannel;
      private volatile DataStreamChannel outputDataChannel;
      private volatile boolean endStream;
  
      public EchoHandler(final int bufferSize) {
          this.initBufferSize = bufferSize;
          this.capacityIncrement = new AtomicInteger();
          this.buffer = ByteBuffer.allocate(bufferSize);
      }
  
      private void ensureCapacity(final int chunk) {
          if (buffer.remaining() < chunk) {
              final ByteBuffer oldBuffer = buffer;
              oldBuffer.flip();
              final int newCapacity = oldBuffer.remaining() + Math.max(chunk, MIN_CHUNK);
              buffer = ByteBuffer.allocate(newCapacity);
              buffer.put(oldBuffer);
          }
      }
  
      private void signalCapacity() throws IOException {
          if (inputCapacityChannel != null) {
              if (capacityIncrement.get() > MIN_CHUNK) {
                  final int n = capacityIncrement.getAndSet(0);
                  if (n > 0) {
                      inputCapacityChannel.update(n);
                  }
              }
          }
      }
  
      @Override
      public void handleRequest(
              final HttpRequest request,
              final EntityDetails entityDetails,
              final ResponseChannel responseChannel,
              final HttpContext context) throws HttpException, IOException {
          final HttpResponse response = new BasicHttpResponse(HttpStatus.SC_OK);
          responseChannel.sendResponse(response, entityDetails, context);
      }
  
      @Override
      public void consume(final ByteBuffer src) throws IOException {
          if (buffer.position() == 0) {
              if (outputDataChannel != null) {
                  final int bytesWritten = outputDataChannel.write(src);
                 if (bytesWritten > 0) {
                     capacityIncrement.addAndGet(bytesWritten);
                 }
             }
         }
         if (src.hasRemaining()) {
             ensureCapacity(src.remaining());
             buffer.put(src);
             if (outputDataChannel != null) {
                 outputDataChannel.requestOutput();
             }
         }
         signalCapacity();
     }
 
     @Override
     public void updateCapacity(final CapacityChannel capacityChannel) throws IOException {
         if (buffer.hasRemaining()) {
             final int n = Math.min(initBufferSize, buffer.remaining()) + capacityIncrement.getAndSet(0);
             capacityChannel.update(n);
         }
         inputCapacityChannel = capacityChannel;
     }
 
     @Override
     public void streamEnd(final List<? extends Header> trailers) throws HttpException, IOException {
         endStream = true;
         inputCapacityChannel = null;
         if (buffer.position() == 0) {
             if (outputDataChannel != null) {
                 outputDataChannel.endStream();
             }
         } else {
             if (outputDataChannel != null) {
                 outputDataChannel.requestOutput();
             }
         }
     }
 
     @Override
     public int available() {
         return buffer.position();
     }
 
     @Override
     public void produce(final DataStreamChannel channel) throws IOException {
         outputDataChannel = channel;
         buffer.flip();
         if (buffer.hasRemaining()) {
             final int bytesWritten = channel.write(buffer);
             if (bytesWritten > 0) {
                 capacityIncrement.addAndGet(bytesWritten);
             }
         }
         buffer.compact();
         if (buffer.position() == 0 && endStream) {
             channel.endStream();
         }
         signalCapacity();
     }
 
     @Override
     public void failed(final Exception cause) {
     }
 
     @Override
     public void releaseResources() {
     }
 
 }