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/**
 * Copyright (C) 2006-2015 phloc systems
 * http://www.phloc.com
 * office[at]phloc[dot]com
 *
 * 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.
 */
package com.phloc.commons.messagedigest;

import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

import javax.annotation.Nonnegative;
import javax.annotation.Nonnull;

import com.phloc.commons.annotations.Nonempty;
import com.phloc.commons.annotations.ReturnsMutableCopy;
import com.phloc.commons.string.ToStringGenerator;

/**
 * Base class for creating a cryptographic hash value. Don't mix it up with the
 * {@link com.phloc.commons.hash.HashCodeGenerator} which is used to generate
 * hash values for Java objects.
 * 
 * @author Philip Helger
 */
public final class MessageDigestGenerator extends AbstractMessageDigestGenerator
{
  private final ReadWriteLock m_aRWLock = new ReentrantReadWriteLock ();
  private final IMessageDigestGenerator m_aMDGen;

  /**
   * Create a default hash generator with the default algorithm.
   */
  public MessageDigestGenerator ()
  {
    this (DEFAULT_ALGORITHM);
  }

  /**
   * Create a hash generator with a set of possible algorithms to use.
   * 
   * @param aAlgorithms
   *        The parameters to test. May not be null.
   * @throws NullPointerException
   *         If the array of algorithms is null or if one element
   *         of the array is null.
   * @throws IllegalArgumentException
   *         If no algorithm was passed or if no applicable algorithm was used.
   */
  public MessageDigestGenerator (@Nonnull @Nonempty final EMessageDigestAlgorithm... aAlgorithms)
  {
    m_aMDGen = new NonBlockingMessageDigestGenerator (aAlgorithms);
  }

  @Nonnull
  public String getAlgorithmName ()
  {
    return m_aMDGen.getAlgorithmName ();
  }

  @Nonnegative
  public int getDigestLength ()
  {
    return m_aMDGen.getDigestLength ();
  }

  @Nonnull
  public MessageDigestGenerator update (final byte aValue)
  {
    m_aRWLock.writeLock ().lock ();
    try
    {
      m_aMDGen.update (aValue);
      return this;
    }
    finally
    {
      m_aRWLock.writeLock ().unlock ();
    }
  }

  @Nonnull
  public MessageDigestGenerator update (@Nonnull final byte [] aValue,
                                        @Nonnegative final int nOffset,
                                        @Nonnegative final int nLength)
  {
    m_aRWLock.writeLock ().lock ();
    try
    {
      m_aMDGen.update (aValue, nOffset, nLength);
      return this;
    }
    finally
    {
      m_aRWLock.writeLock ().unlock ();
    }
  }

  public void reset ()
  {
    m_aRWLock.writeLock ().lock ();
    try
    {
      m_aMDGen.reset ();
    }
    finally
    {
      m_aRWLock.writeLock ().unlock ();
    }
  }

  @Nonnull
  @ReturnsMutableCopy
  public byte [] getDigest ()
  {
    m_aRWLock.writeLock ().lock ();
    try
    {
      return m_aMDGen.getDigest ();
    }
    finally
    {
      m_aRWLock.writeLock ().unlock ();
    }
  }

  @Nonnull
  @ReturnsMutableCopy
  public byte [] getDigest (@Nonnegative final int nLength)
  {
    // Using a writeLock because it calculates the main digest on first call
    m_aRWLock.writeLock ().lock ();
    try
    {
      return m_aMDGen.getDigest (nLength);
    }
    finally
    {
      m_aRWLock.writeLock ().unlock ();
    }
  }

  @Override
  public String toString ()
  {
    return new ToStringGenerator (this).append ("messageDigestGenerator", m_aMDGen).toString ();
  }
}