/* BasePad.java -- 
   Copyright (C) 2001, 2002, 2003, 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
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General Public License for more details.

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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
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package gnu.javax.crypto.pad;

import gnu.java.security.Configuration;

import java.util.Map;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * An abstract class to facilitate implementing padding algorithms.
 */
public abstract class BasePad
    implements IPad
{
  private static final Logger log = Logger.getLogger(BasePad.class.getName());
  /** The canonical name prefix of the padding algorithm. */
  protected String name;
  /** The block size, in bytes, for this instance. */
  protected int blockSize;

  /** Trivial constructor for use by concrete subclasses. */
  protected BasePad(final String name)
  {
    super();

    this.name = name;
    blockSize = -1;
  }

  public String name()
  {
    final StringBuffer sb = new StringBuffer(name);
    if (blockSize != -1)
      sb.append('-').append(String.valueOf(8 * blockSize));
    return sb.toString();
  }

  public void init(final int bs) throws IllegalStateException
  {
    if (blockSize != -1)
      throw new IllegalStateException();
    blockSize = bs;
    setup();
  }

  /**
   * Initialises the algorithm with designated attributes. Names, valid and/or
   * recognisable by all concrete implementations are described in {@link IPad}
   * class documentation. Other algorithm-specific attributes MUST be documented
   * in the implementation class of that padding algorithm.
   * <p>
   * For compatibility reasons, this method is not declared <i>abstract</i>.
   * Furthermore, and unless overridden, the default implementation will throw
   * an {@link UnsupportedOperationException}. Concrete padding algorithms MUST
   * override this method if they wish to offer an initialisation method that
   * allows for other than the padding block size parameter to be specified.
   * 
   * @param attributes a set of name-value pairs that describes the desired
   *          future behaviour of this instance.
   * @exception IllegalStateException if the instance is already initialised.
   * @exception IllegalArgumentException if the block size value is invalid.
   */
  public void init(Map attributes) throws IllegalStateException
  {
    throw new UnsupportedOperationException();
  }

  public void reset()
  {
    blockSize = -1;
  }

  /**
   * A default implementation of a correctness test that exercises the padder
   * implementation, using block sizes varying from 2 to 256 bytes.
   * 
   * @return <code>true</code> if the concrete implementation correctly unpads
   *         what it pads for all tested block sizes. Returns <code>false</code>
   *         if the test fails for any block size.
   */
  public boolean selfTest()
  {
    final byte[] in = new byte[1024];
    for (int bs = 2; bs < 256; bs++)
      if (! test1BlockSize(bs, in))
        return false;
    return true;
  }

  /**
   * The basic symmetric test for a padder given a specific block size.
   * <p>
   * The code ensures that the implementation is capable of unpadding what it
   * pads.
   * 
   * @param size the block size to test.
   * @param buffer a work buffer. It is exposed as an argument for this method
   *          to reduce un-necessary object allocations.
   * @return <code>true</code> if the test passes; <code>false</code>
   *         otherwise.
   */
  protected boolean test1BlockSize(int size, byte[] buffer)
  {
    byte[] padBytes;
    final int offset = 5;
    final int limit = buffer.length;
    this.init(size);
    for (int i = 0; i < limit - offset - blockSize; i++)
      {
        padBytes = pad(buffer, offset, i);
        if (((i + padBytes.length) % blockSize) != 0)
          {
            if (Configuration.DEBUG)
              log.log(Level.SEVERE,
                      "Length of padded text MUST be a multiple of "
                      + blockSize, new RuntimeException(name()));
            return false;
          }
        System.arraycopy(padBytes, 0, buffer, offset + i, padBytes.length);
        try
          {
            if (padBytes.length != unpad(buffer, offset, i + padBytes.length))
              {
                if (Configuration.DEBUG)
                  log.log(Level.SEVERE,
                          "IPad [" + name() + "] failed symmetric operation",
                          new RuntimeException(name()));
                return false;
              }
          }
        catch (WrongPaddingException x)
          {
            if (Configuration.DEBUG)
              log.throwing(this.getClass().getName(), "test1BlockSize", x);
            return false;
          }
      }
    this.reset();
    return true;
  }

  /**
   * If any additional checks or resource setup must be done by the subclass,
   * then this is the hook for it. This method will be called before the
   * {@link #init(int)} method returns.
   */
  public abstract void setup();

  public abstract byte[] pad(byte[] in, int off, int len);

  public abstract int unpad(byte[] in, int off, int len)
      throws WrongPaddingException;
}