package org.eclipse.aether.connector.basic;
   
   /*
    * 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.
   */
  
  import java.io.File;
  import java.io.FileInputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.nio.Buffer;
  import java.nio.ByteBuffer;
  import java.security.MessageDigest;
  import java.security.NoSuchAlgorithmException;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.List;
  import java.util.Map;
  import java.util.Set;
  
  import org.eclipse.aether.spi.connector.layout.RepositoryLayout;
  import org.eclipse.aether.util.ChecksumUtils;
  
  /**
   * Calculates checksums for a downloaded file.
   */
  final class ChecksumCalculator
  {
  
      static class Checksum
      {
          final String algorithm;
  
          final MessageDigest digest;
  
          Exception error;
  
          Checksum( String algorithm )
          {
              this.algorithm = algorithm;
              MessageDigest digest = null;
              try
              {
                  digest = MessageDigest.getInstance( algorithm );
              }
              catch ( NoSuchAlgorithmException e )
              {
                  error = e;
              }
              this.digest = digest;
          }
  
          public void update( ByteBuffer buffer )
          {
              if ( digest != null )
              {
                  digest.update( buffer );
              }
          }
  
          public void reset()
          {
              if ( digest != null )
              {
                  digest.reset();
                  error = null;
              }
          }
  
          public void error( Exception error )
          {
              if ( digest != null )
              {
                  this.error = error;
              }
          }
  
          public Object get()
          {
              if ( error != null )
              {
                  return error;
             }
             return ChecksumUtils.toHexString( digest.digest() );
         }
 
     }
 
     private final List<Checksum> checksums;
 
     private final File targetFile;
 
     public static ChecksumCalculator newInstance( File targetFile, Collection<RepositoryLayout.Checksum> checksums )
     {
         if ( checksums == null || checksums.isEmpty() )
         {
             return null;
         }
         return new ChecksumCalculator( targetFile, checksums );
     }
 
     private ChecksumCalculator( File targetFile, Collection<RepositoryLayout.Checksum> checksums )
     {
         this.checksums = new ArrayList<>();
         Set<String> algos = new HashSet<>();
         for ( RepositoryLayout.Checksum checksum : checksums )
         {
             String algo = checksum.getAlgorithm();
             if ( algos.add( algo ) )
             {
                 this.checksums.add( new Checksum( algo ) );
             }
         }
         this.targetFile = targetFile;
     }
 
     public void init( long dataOffset )
     {
         for ( Checksum checksum : checksums )
         {
             checksum.reset();
         }
         if ( dataOffset <= 0L )
         {
             return;
         }
 
         InputStream in = null;
         try
         {
             in = new FileInputStream( targetFile );
             long total = 0;
             ByteBuffer buffer = ByteBuffer.allocate( 1024 * 32 );
             for ( byte[] array = buffer.array(); total < dataOffset; )
             {
                 int read = in.read( array );
                 if ( read < 0 )
                 {
                     if ( total < dataOffset )
                     {
                         throw new IOException( targetFile + " contains only " + total
                                                    + " bytes, cannot resume download from offset " + dataOffset );
                     }
                     break;
                 }
                 total += read;
                 if ( total > dataOffset )
                 {
                     read -= total - dataOffset;
                 }
                 ( (Buffer) buffer ).rewind();
                 ( (Buffer) buffer ).limit( read );
                 update( buffer );
             }
 
             in.close();
             in = null;
         }
         catch ( IOException e )
         {
             for ( Checksum checksum : checksums )
             {
                 checksum.error( e );
             }
         }
         finally
         {
             try
             {
                 if ( in != null )
                 {
                     in.close();
                 }
             }
             catch ( IOException e )
             {
                 // Suppressed due to an exception already thrown in the try block.
             }
         }
     }
 
     public void update( ByteBuffer data )
     {
         for ( Checksum checksum : checksums )
         {
             ( (Buffer) data ).mark();
             checksum.update( data );
             ( (Buffer) data ).reset();
         }
     }
 
     public Map<String, Object> get()
     {
         Map<String, Object> results = new HashMap<>();
         for ( Checksum checksum : checksums )
         {
             results.put( checksum.algorithm, checksum.get() );
         }
         return results;
     }
 
 }