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package gnu.crypto.hash;

// ----------------------------------------------------------------------------
// $Id: BaseHash.java,v 1.8 2002/11/07 17:17:45 raif Exp $
//
// Copyright (C) 2001, 2002, Free Software Foundation, Inc.
//
// This file is part of GNU Crypto.
//
// GNU Crypto 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, or (at your option)
// any later version.
//
// GNU Crypto is distributed in the hope that it will be useful, but
// 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.
//
// You should have received a copy of the GNU General Public License
// along with this program; see the file COPYING.  If not, write to the
//
//    Free Software Foundation Inc.,
//    59 Temple Place - Suite 330,
//    Boston, MA 02111-1307
//    USA
//
// Linking this library statically or dynamically with other modules is
// making a combined work based on this library.  Thus, the terms and
// conditions of the GNU General Public License cover the whole
// combination.
//
// As a special exception, the copyright holders of this library give
// you permission to link this library with independent modules to
// produce an executable, regardless of the license terms of these
// independent modules, and to copy and distribute the resulting
// executable under terms of your choice, provided that you also meet,
// for each linked independent module, the terms and conditions of the
// license of that module.  An independent module is a module which is
// not derived from or based on this library.  If you modify this
// library, you may extend this exception to your version of the
// library, but you are not obligated to do so.  If you do not wish to
// do so, delete this exception statement from your version.
// ----------------------------------------------------------------------------
/**
 * 
 * A base abstract class to facilitate hash implementations.
 *
 * @version $Revision: 1.8 $
 */
public abstract class BaseHash implements IMessageDigest {

    // Constants and variables
    // -------------------------------------------------------------------------
    /**
     * 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;

    // Constructor(s)
    // -------------------------------------------------------------------------
    /**
     * 
     * 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();
    }

    // Class methods
    // -------------------------------------------------------------------------
    // Instance methods
    // -------------------------------------------------------------------------
    // IMessageDigest interface implementation ---------------------------------
    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, 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();
    }

    // methods to be implemented by concrete subclasses ------------------------
    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 blockSize 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);
}