package gnu.crypto.assembly;

// ----------------------------------------------------------------------------
// $Id: PaddingTransformer.java,v 1.2 2005/10/06 04:24:13 rsdio Exp $
//
// Copyright (C) 2003, 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.,
//    51 Franklin Street, 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
// 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.
// ----------------------------------------------------------------------------

import gnu.crypto.pad.IPad;
import gnu.crypto.pad.WrongPaddingException;

import java.util.Map;

/**
 * <p>An Adapter to use any {@link IPad} as a {@link Transformer} in an
 * {@link Assembly}.</p>
 *
 * <p>When using such a {@link Transformer}, in an {@link Assembly}, there must
 * be at least one element behind this instance in the constructed chain;
 * otherwise, a {@link TransformerException} is thrown at initialisation time.</p>
 *
 * @version $Revision: 1.2 $
 */
class PaddingTransformer extends Transformer {

   // Constants and variables
   // -------------------------------------------------------------------------

   private IPad delegate;
   private int outputBlockSize = 1;

   // Constructor(s)
   // -------------------------------------------------------------------------

   PaddingTransformer(IPad padding) {
      super();

      this.delegate = padding;
   }

   // Class methods
   // -------------------------------------------------------------------------

   // Instance methods
   // -------------------------------------------------------------------------

   void initDelegate(Map attributes) throws TransformerException {
      if (tail == null) {
         throw new TransformerException("initDelegate()",
               new IllegalStateException("Padding transformer missing its tail!"));
      }
      outputBlockSize = tail.currentBlockSize();
      delegate.init(outputBlockSize);
   }

   int delegateBlockSize() {
      return outputBlockSize;
   }

   void resetDelegate() {
      delegate.reset();
      outputBlockSize = 1;
   }

   byte[] updateDelegate(byte[] in, int offset, int length) throws TransformerException {
      inBuffer.write(in, offset, length);
      byte[] tmp = inBuffer.toByteArray();
      inBuffer.reset();
      byte[] result;
      if (wired == Direction.FORWARD) { // padding
         // buffers remaining bytes from (inBuffer + in) that are less than 1 block
         if (tmp.length < outputBlockSize) {
            inBuffer.write(tmp, 0, tmp.length);
            result = new byte[0];
         } else {
            int newlen = outputBlockSize * (tmp.length / outputBlockSize);
            inBuffer.write(tmp, newlen, tmp.length - newlen);
            result = new byte[newlen];
            System.arraycopy(tmp, 0, result, 0, newlen);
         }
      } else { // unpadding
         // always keep in own buffer a max of 1 block to cater for lastUpdate
         if (tmp.length < outputBlockSize) {
            inBuffer.write(tmp, 0, tmp.length);
            result = new byte[0];
         } else {
            result = new byte[tmp.length - outputBlockSize];
            System.arraycopy(tmp, 0, result, 0, result.length);
            inBuffer.write(tmp, result.length, outputBlockSize);
         }
      }
      return result;
   }

   byte[] lastUpdateDelegate() throws TransformerException {
      byte[] result;
      // process multiples of blocksize as much as possible
      // catenate result from processing inBuffer with last-update( tail )
      if (wired == Direction.FORWARD) { // padding
         result = inBuffer.toByteArray();
         byte[] padding = delegate.pad(result, 0, result.length);
         inBuffer.write(padding, 0, padding.length);
      } else { // unpadding
         byte[] tmp = inBuffer.toByteArray();
         inBuffer.reset();
         int realLength;
         try {
            realLength = tmp.length; // should be outputBlockSize
            realLength -= delegate.unpad(tmp, 0, tmp.length);
         } catch (WrongPaddingException x) {
            throw new TransformerException("lastUpdateDelegate()", x);
         }
         inBuffer.write(tmp, 0, realLength);
      }
      result = inBuffer.toByteArray();
      inBuffer.reset();
      return result;
   }
}
