/*
    * ====================================================================
    * 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.http.nio.entity;
  
  import java.io.IOException;
  import java.nio.ByteBuffer;
  import java.security.MessageDigest;
  import java.security.NoSuchAlgorithmException;
  import java.util.ArrayList;
  import java.util.List;
  
  import org.apache.hc.core5.concurrent.FutureCallback;
  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.nio.AsyncEntityConsumer;
  import org.apache.hc.core5.http.nio.CapacityChannel;
  import org.apache.hc.core5.util.Args;
  
  /**
   * {@link AsyncEntityConsumer} decorator that calculates a digest hash from
   * the data stream content and keeps the list of trailers received with
   * the data stream.
   *
   * @since 5.0
   */
  public class DigestingEntityConsumer<T> implements AsyncEntityConsumer<T> {
  
      private final AsyncEntityConsumer<T> wrapped;
      private final List<Header> trailers;
      private final MessageDigest digester;
  
      private volatile byte[] digest;
  
      public DigestingEntityConsumer(
              final String algo,
              final AsyncEntityConsumer<T> wrapped) throws NoSuchAlgorithmException {
          this.wrapped = Args.notNull(wrapped, "Entity consumer");
          this.trailers = new ArrayList<>();
          this.digester = MessageDigest.getInstance(algo);
      }
  
      @Override
      public void streamStart(
              final EntityDetails entityDetails,
              final FutureCallback<T> resultCallback) throws IOException, HttpException {
          wrapped.streamStart(entityDetails, resultCallback);
      }
  
      @Override
      public void updateCapacity(final CapacityChannel capacityChannel) throws IOException {
          wrapped.updateCapacity(capacityChannel);
      }
  
      @Override
      public void consume(final ByteBuffer src) throws IOException {
          src.mark();
          digester.update(src);
          src.reset();
          wrapped.consume(src);
      }
  
      @Override
      public void streamEnd(final List<? extends Header> trailers) throws HttpException, IOException {
          if (trailers != null) {
              this.trailers.addAll(trailers);
          }
          digest = digester.digest();
          wrapped.streamEnd(trailers);
      }
  
      @Override
      public void failed(final Exception cause) {
          wrapped.failed(cause);
      }
 
     @Override
     public T getContent() {
         return wrapped.getContent();
     }
 
     @Override
     public void releaseResources() {
         wrapped.releaseResources();
     }
 
     /**
      * List of trailers sent with the data stream.
      *
      * @return the list of trailers sent with the data stream
      */
     public List<Header> getTrailers() {
         return trailers != null ? new ArrayList<>(trailers) : null;
     }
 
     /**
      * Returns digest hash.
      *
      * @return the digest hash value.
      */
     public byte[] getDigest() {
         return digest;
     }
 
 }