/*
    * ====================================================================
    * 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.LinkedHashSet;
  import java.util.List;
  import java.util.Set;
  
  import org.apache.hc.core5.http.Header;
  import org.apache.hc.core5.http.message.BasicHeader;
  import org.apache.hc.core5.http.nio.AsyncEntityProducer;
  import org.apache.hc.core5.http.nio.DataStreamChannel;
  import org.apache.hc.core5.util.Args;
  import org.apache.hc.core5.util.TextUtils;
  
  /**
   * {@link AsyncEntityProducer} decorator that calculates a digest hash from
   * the data stream content and appends its value to the list of trailers.
   *
   * @since 5.0
   */
  public class DigestingEntityProducer implements AsyncEntityProducer {
  
      private final AsyncEntityProducer wrapped;
      private final MessageDigest digester;
  
      private volatile byte[] digest;
  
      public DigestingEntityProducer(
              final String algo,
              final AsyncEntityProducer wrapped) {
          this.wrapped = Args.notNull(wrapped, "Entity consumer");
          try {
              this.digester = MessageDigest.getInstance(algo);
          } catch (final NoSuchAlgorithmException ex) {
              throw new IllegalArgumentException("Unsupported digest algorithm: " + algo);
          }
      }
  
      @Override
      public boolean isRepeatable() {
          return wrapped.isRepeatable();
      }
  
      @Override
      public long getContentLength() {
          return wrapped.getContentLength();
      }
  
      @Override
      public String getContentType() {
          return wrapped.getContentType();
      }
  
      @Override
      public String getContentEncoding() {
          return wrapped.getContentEncoding();
      }
  
      @Override
      public boolean isChunked() {
          return wrapped.isChunked();
      }
  
      @Override
      public Set<String> getTrailerNames() {
          final Set<String> allNames = new LinkedHashSet<>();
          final Set<String> names = wrapped.getTrailerNames();
          if (names != null) {
              allNames.addAll(names);
         }
         allNames.add("digest-algo");
         allNames.add("digest");
         return allNames;
     }
 
     @Override
     public int available() {
         return wrapped.available();
     }
 
     @Override
     public void produce(final DataStreamChannel channel) throws IOException {
         wrapped.produce(new DataStreamChannel() {
 
             @Override
             public void requestOutput() {
                 channel.requestOutput();
             }
 
             @Override
             public int write(final ByteBuffer src) throws IOException {
                 final ByteBuffer dup = src.duplicate();
                 final int writtenBytes = channel.write(src);
                 if (writtenBytes > 0) {
                     dup.limit(dup.position() + writtenBytes);
                     digester.update(dup);
                 }
                 return writtenBytes;
             }
 
             @Override
             public void endStream(final List<? extends Header> trailers) throws IOException {
                 digest = digester.digest();
                 final List<Header> allTrailers = new ArrayList<>();
                 if (trailers != null) {
                     allTrailers.addAll(trailers);
                 }
                 allTrailers.add(new BasicHeader("digest-algo", digester.getAlgorithm()));
                 allTrailers.add(new BasicHeader("digest", TextUtils.toHexString(digest)));
                 channel.endStream(allTrailers);
             }
 
             @Override
             public void endStream() throws IOException {
                 endStream(null);
             }
 
         });
     }
 
     @Override
     public void failed(final Exception cause) {
         wrapped.failed(cause);
     }
 
     @Override
     public void releaseResources() {
         wrapped.releaseResources();
     }
 
     /**
      * Returns digest hash.
      *
      * @return the digest hash value.
      */
     public byte[] getDigest() {
         return digest;
     }
 
 }