/* BaseHash.java -- 
   Copyright (C) 2001, 2002, 2006 Free Software Foundation, Inc.

This file is a part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at
your option) any later version.

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WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
USA

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
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permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
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package gnu.java.security.hash;

/**
 * A base abstract class to facilitate hash implementations.
 */
public abstract class BaseHash
    implements IMessageDigest
{
  /** The canonical name prefix of the hash. */
  protected String name;

  /** The hash (output) size in bytes. */
  protected int hashSize;

  /** The hash (inner) block size in bytes. */
  protected int blockSize;

  /** Number of bytes processed so far. */
  protected long count;

  /** Temporary input buffer. */
  protected byte[] buffer;

  /**
   * Trivial constructor for use by concrete subclasses.
   * 
   * @param name the canonical name prefix of this instance.
   * @param hashSize the block size of the output in bytes.
   * @param blockSize the block size of the internal transform.
   */
  protected BaseHash(String name, int hashSize, int blockSize)
  {
    super();

    this.name = name;
    this.hashSize = hashSize;
    this.blockSize = blockSize;
    this.buffer = new byte[blockSize];

    resetContext();
  }

  public String name()
  {
    return name;
  }

  public int hashSize()
  {
    return hashSize;
  }

  public int blockSize()
  {
    return blockSize;
  }

  public void update(byte b)
  {
    // compute number of bytes still unhashed; ie. present in buffer
    int i = (int) (count % blockSize);
    count++;
    buffer[i] = b;
    if (i == (blockSize - 1))
      transform(buffer, 0);
  }

  public void update(byte[] b)
  {
    update(b, 0, b.length);
  }

  public void update(byte[] b, int offset, int len)
  {
    int n = (int) (count % blockSize);
    count += len;
    int partLen = blockSize - n;
    int i = 0;

    if (len >= partLen)
      {
        System.arraycopy(b, offset, buffer, n, partLen);
        transform(buffer, 0);
        for (i = partLen; i + blockSize - 1 < len; i += blockSize)
          transform(b, offset + i);

        n = 0;
      }

    if (i < len)
      System.arraycopy(b, offset + i, buffer, n, len - i);
  }

  public byte[] digest()
  {
    byte[] tail = padBuffer(); // pad remaining bytes in buffer
    update(tail, 0, tail.length); // last transform of a message
    byte[] result = getResult(); // make a result out of context

    reset(); // reset this instance for future re-use

    return result;
  }

  public void reset()
  { // reset this instance for future re-use
    count = 0L;
    for (int i = 0; i < blockSize;)
      buffer[i++] = 0;

    resetContext();
  }

  public abstract Object clone();

  public abstract boolean selfTest();

  /**
   * Returns the byte array to use as padding before completing a hash
   * operation.
   * 
   * @return the bytes to pad the remaining bytes in the buffer before
   *         completing a hash operation.
   */
  protected abstract byte[] padBuffer();

  /**
   * Constructs the result from the contents of the current context.
   * 
   * @return the output of the completed hash operation.
   */
  protected abstract byte[] getResult();

  /** Resets the instance for future re-use. */
  protected abstract void resetContext();

  /**
   * The block digest transformation per se.
   * 
   * @param in the <i>blockSize</i> long block, as an array of bytes to digest.
   * @param offset the index where the data to digest is located within the
   *          input buffer.
   */
  protected abstract void transform(byte[] in, int offset);
}