package org.codehaus.plexus.digest;
   
   /*
    * Copyright 2001-2006 The Codehaus.
    *
    * Licensed 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.
   */
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.security.MessageDigest;
  import java.security.NoSuchAlgorithmException;
  
  /**
   * Gradually create a digest for a stream.
   *
   * @author <a href="mailto:brett@apache.org">Brett Porter</a>
   */
  public abstract class AbstractStreamingDigester
      implements StreamingDigester
  {
      protected final MessageDigest md;
  
      private static final int BUFFER_SIZE = 32768;
  
      protected AbstractStreamingDigester( String algorithm )
      {
          try
          {
              md = MessageDigest.getInstance( algorithm );
          }
          catch ( NoSuchAlgorithmException e )
          {
              throw new IllegalStateException( "Unable to initialize digest algorithm " + algorithm + " : "
                  + e.getMessage() );
          }
      }
  
      public String getAlgorithm()
      {
          return md.getAlgorithm();
      }
  
      public String calc()
          throws DigesterException
      {
          return calc( this.md );
      }
  
      public void reset()
          throws DigesterException
      {
          md.reset();
      }
  
      public void update( InputStream is )
          throws DigesterException
      {
          update( is, md );
      }
  
      protected static String calc( MessageDigest md )
      {
          return Hex.encode( md.digest() );
      }
  
      protected static void update( InputStream is, MessageDigest digest )
          throws DigesterException
      {
          try
          {
              byte[] buffer = new byte[BUFFER_SIZE];
              int size = is.read( buffer, 0, BUFFER_SIZE );
              while ( size >= 0 )
              {
                  digest.update( buffer, 0, size );
                  size = is.read( buffer, 0, BUFFER_SIZE );
              }
          }
          catch ( IOException e )
          {
              throw new DigesterException( "Unable to update " + digest.getAlgorithm() + " hash: " + e.getMessage(), e );
          }
      }
  }