package org.apache.archiva.checksum;
   
   /*
    * 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.IOException;
  import java.nio.ByteBuffer;
  import java.nio.MappedByteBuffer;
  import java.nio.channels.FileChannel;
  import java.nio.file.Path;
  import java.nio.file.StandardOpenOption;
  import java.security.MessageDigest;
  import java.security.NoSuchAlgorithmException;
  
  /**
   * Checksum - simple checksum hashing routines.
   */
  public class Checksum
  {
      private byte[] result = new byte[0];
  
      private final MessageDigest md;
  
      private ChecksumAlgorithm checksumAlgorithm;
  
      public Checksum( ChecksumAlgorithm checksumAlgorithm )
      {
          this.checksumAlgorithm = checksumAlgorithm;
          try
          {
              md = MessageDigest.getInstance( checksumAlgorithm.getAlgorithm() );
          }
          catch ( NoSuchAlgorithmException e )
          {
              // Not really possible, but here none-the-less
              throw new IllegalStateException(
                  "Unable to initialize MessageDigest algorithm " + checksumAlgorithm.getAlgorithm() + " : "
                      + e.getMessage(), e );
          }
      }
  
      public String getChecksum()
      {
          if (this.result.length==0) {
              finish();
          }
          return Hex.encode( this.result );
      }
  
      public byte[] getChecksumBytes() {
          if (this.result.length==0) {
              finish();
          }
          return this.result;
      }
  
      public ChecksumAlgorithm getAlgorithm()
      {
          return this.checksumAlgorithm;
      }
  
      public void reset()
      {
          md.reset();
          this.result = new byte[0];
      }
  
      public Checksum update( byte[] buffer, int offset, int size )
      {
          if (this.result.length!=0) {
              reset();
          }
          md.update( buffer, 0, size );
          return this;
      }
  
      public Checksum update( ByteBuffer buffer)
      {
          if (this.result.length!=0) {
              reset();
          }
          md.update( buffer );
          return this;
     }
 
     public Checksum finish() {
         this.result = md.digest();
         return this;
     }
 
     public boolean compare(byte[] cmp) {
         if (this.result == null || this.result.length==0) {
             finish();
         }
         return md.isEqual( this.result, cmp );
     }
 
     public boolean compare(String hexString) {
         if (this.result == null || this.result.length==0) {
             finish();
         }
         return md.isEqual(this.result, Hex.decode( hexString ));
     }
 }