/* Transformer.java -- 
   Copyright (C) 2003, 2006 Free Software Foundation, Inc.

This file is a part of GNU Classpath.

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it under the terms of the GNU General Public License as published by
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Linking this library statically or dynamically with other modules is
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package gnu.javax.crypto.assembly;

import gnu.javax.crypto.pad.IPad;

import java.io.ByteArrayOutputStream;
import java.util.Map;

/**
 * A <code>Transformer</code> is an abstract representation of a two-way
 * <i>transformation</i> that can be chained together with other instances of
 * this type. Examples of such transformations in this library are:
 * {@link Cascade} cipher, {@link gnu.javax.crypto.pad.IPad} algorithm, and a
 * ZLib-based deflater/inflater algorithm. A special implementation of a
 * <code>Transformer</code> to close a chain is also provided.
 * <p>
 * A <code>Transformer</code> is characterised by the followings:
 * <ul>
 * <li>It can be chained to other instances, to form an {@link Assembly}.</li>
 * <li>When configured in an {@link Assembly}, it can be set to apply its
 * internal transformation on the input data stream before (pre-processing) or
 * after (post-processing) passing the input data to the next element in the
 * chain. Note that the same type <code>Transformer</code> can be used as
 * either in pre-processing or a post-processing modes.</li>
 * <li>A special transformer --<code>LoopbackTransformer</code>-- is used
 * to close the chain.</li>
 * <li>A useful type of <code>Transformer</code> --one we're interested in--
 * has internal buffers. The distinction between a casual push (update)
 * operation and the last one allows to correctly flush any intermediate bytes
 * that may exist in those buffers.</li>
 * </ul>
 * <p>
 * To allow wiring <code>Transformer</code> instances together, a
 * <i>minimal-output-size</i> in bytes is necessary. The trivial case of a
 * value of <code>1</code> for such attribute practically means that no output
 * buffering, from the previous element, is needed --which is independant of
 * buffering the input if the <code>Transformer</code> implementation itself
 * is block-based.
 * 
 * @see CascadeTransformer
 * @see PaddingTransformer
 * @see DeflateTransformer
 */
public abstract class Transformer
{
  public static final String DIRECTION = "gnu.crypto.assembly.transformer.direction";

  protected Direction wired;

  protected Operation mode;

  protected Transformer tail = null;

  protected ByteArrayOutputStream inBuffer = new ByteArrayOutputStream(2048);

  protected ByteArrayOutputStream outBuffer = new ByteArrayOutputStream(2048);

  /** Trivial protected constructor. */
  protected Transformer()
  {
    super();

    this.wired = null;
  }

  public static final Transformer getCascadeTransformer(Cascade cascade)
  {
    return new CascadeTransformer(cascade);
  }

  public static final Transformer getPaddingTransformer(IPad padding)
  {
    return new PaddingTransformer(padding);
  }

  public static final Transformer getDeflateTransformer()
  {
    return new DeflateTransformer();
  }

  /**
   * Sets the operational mode of this <code>Transformer</code>.
   * 
   * @param mode the processing mode this <code>Transformer</code> is required
   *          to operate in.
   * @throws IllegalStateException if this instance has already been assigned an
   *           operational mode.
   */
  public void setMode(final Operation mode)
  {
    if (this.mode != null)
      throw new IllegalStateException();
    this.mode = mode;
  }

  /**
   * Returns <code>true</code> if this <code>Transformer</code> was wired in
   * pre-processing mode; <code>false</code> otherwise.
   * 
   * @return <code>true</code> if this <code>Transformer</code> has been
   *         wired in pre-processing mode; <code>false</code> otherwise.
   * @throws IllegalStateException if this instance has not yet been assigned an
   *           operational <i>type</i>.
   */
  public boolean isPreProcessing()
  {
    if (mode == null)
      throw new IllegalStateException();
    return (mode == Operation.PRE_PROCESSING);
  }

  /**
   * Returns <code>true</code> if this <code>Transformer</code> was wired in
   * post-processing mode; <code>false</code> otherwise.
   * 
   * @return <code>true</code> if this <code>Transformer</code> has been
   *         wired in post-processing mode; <code>false</code> otherwise.
   * @throws IllegalStateException if this instance has not yet been assigned an
   *           operational <i>type</i>.
   */
  public boolean isPostProcessing()
  {
    return ! isPreProcessing();
  }

  /**
   * Initialises the <code>Transformer</code> for operation with specific
   * characteristics.
   * 
   * @param attributes a set of name-value pairs that describes the desired
   *          future behaviour of this instance.
   * @throws IllegalStateException if the instance is already initialised.
   */
  public void init(Map attributes) throws TransformerException
  {
    if (wired != null)
      throw new IllegalStateException();
    Direction flow = (Direction) attributes.get(DIRECTION);
    if (flow == null)
      flow = Direction.FORWARD;
    wired = flow;
    inBuffer.reset();
    outBuffer.reset();
    tail.init(attributes); // initialise tail first
    initDelegate(attributes); // initialise this instance
  }

  /**
   * Returns the block-size of this <code>Transformer</code>. A value of
   * <code>1</code> indicates that this instance is block-agnostic.
   * 
   * @return the current minimal required block size.
   */
  public int currentBlockSize()
  {
    if (wired == null)
      throw new IllegalStateException();
    return delegateBlockSize();
  }

  /**
   * Resets the <code>Transformer</code> for re-initialisation and use with
   * other characteristics. This method always succeeds.
   */
  public void reset()
  {
    resetDelegate();
    wired = null;
    inBuffer.reset();
    outBuffer.reset();
    tail.reset(); // reset tail last
  }

  /**
   * Convenience method that calls the method with same name and three
   * arguments, using a byte array of length <code>1</code> whose contents are
   * the designated byte.
   * 
   * @param b the byte to process.
   * @return the result of transformation.
   * @throws IllegalStateException if the instance is not initialised.
   * @throws TransformerException if a transformation-related exception occurs
   *           during the operation.
   * @see #update(byte[], int, int)
   */
  public byte[] update(byte b) throws TransformerException
  {
    return update(new byte[] { b }, 0, 1);
  }

  /**
   * Convenience method that calls the same method with three arguments. All
   * bytes in <code>in</code>, starting from index position <code>0</code>
   * are considered.
   * 
   * @param in the input data bytes.
   * @return the result of transformation.
   * @throws IllegalStateException if the instance is not initialised.
   * @throws TransformerException if a transformation-related exception occurs
   *           during the operation.
   * @see #update(byte[], int, int)
   */
  public byte[] update(byte[] in) throws TransformerException
  {
    return update(in, 0, in.length);
  }

  /**
   * Processes a designated number of bytes from a given byte array.
   * 
   * @param in the input data bytes.
   * @param offset index of <code>in</code> from which to start considering
   *          data.
   * @param length the count of bytes to process.
   * @return the result of transformation.
   * @throws IllegalStateException if the instance is not initialised.
   * @throws TransformerException if a transformation-related exception occurs
   *           during the operation.
   */
  public byte[] update(byte[] in, int offset, int length)
      throws TransformerException
  {
    if (wired == null)
      throw new IllegalStateException();
    byte[] result = (wired == Direction.FORWARD ? forwardUpdate(in, offset, length)
                                                : inverseUpdate(in, offset, length));
    return result;
  }

  /**
   * Convenience method that calls the same method with three arguments. A
   * zero-long byte array is used.
   * 
   * @return the result of transformation.
   * @throws IllegalStateException if the instance is not initialised.
   * @throws TransformerException if a transformation-related exception occurs
   *           during the operation.
   * @see #lastUpdate(byte[], int, int)
   */
  public byte[] lastUpdate() throws TransformerException
  {
    byte[] result = (wired == Direction.FORWARD ? lastForwardUpdate()
                                                : lastInverseUpdate());
    if (inBuffer.size() != 0) // we still have some buffered bytes
      throw new TransformerException("lastUpdate(): input buffer not empty");
    return result;
  }

  /**
   * Convenience method that calls the method with same name and three
   * arguments, using a byte array of length <code>1</code> whose contents are
   * the designated byte.
   * 
   * @param b the byte to process.
   * @return the result of transformation.
   * @throws IllegalStateException if the instance is not initialised.
   * @throws TransformerException if a transformation-related exception occurs
   *           during the operation.
   * @see #lastUpdate(byte[], int, int)
   */
  public byte[] lastUpdate(byte b) throws TransformerException
  {
    return lastUpdate(new byte[] { b }, 0, 1);
  }

  /**
   * Convenience method that calls the same method with three arguments. All
   * bytes in <code>in</code>, starting from index position <code>0</code>
   * are considered.
   * 
   * @param in the input data bytes.
   * @return the result of transformation.
   * @throws IllegalStateException if the instance is not initialised.
   * @throws TransformerException if a transformation-related exception occurs
   *           during the operation.
   * @see #lastUpdate(byte[], int, int)
   */
  public byte[] lastUpdate(byte[] in) throws TransformerException
  {
    return lastUpdate(in, 0, in.length);
  }

  /**
   * Processes a designated number of bytes from a given byte array and signals,
   * at the same time, that this is the last <i>push</i> operation on this
   * <code>Transformer</code>.
   * 
   * @param in the input data bytes.
   * @param offset index of <code>in</code> from which to start considering
   *          data.
   * @param length the count of bytes to process.
   * @return the result of transformation.
   * @throws IllegalStateException if the instance is not initialised.
   * @throws TransformerException if a transformation-related exception occurs
   *           during the operation.
   */
  public byte[] lastUpdate(byte[] in, int offset, int length)
      throws TransformerException
  {
    byte[] result = update(in, offset, length);
    byte[] rest = lastUpdate();
    if (rest.length > 0)
      {
        byte[] newResult = new byte[result.length + rest.length];
        System.arraycopy(result, 0, newResult, 0, result.length);
        System.arraycopy(rest, 0, newResult, result.length, rest.length);
        result = newResult;
      }
    return result;
  }

  private byte[] forwardUpdate(byte[] in, int off, int len)
      throws TransformerException
  {
    return (isPreProcessing() ? preTransform(in, off, len)
                              : postTransform(in, off, len));
  }

  private byte[] inverseUpdate(byte[] in, int off, int len)
      throws TransformerException
  {
    return (isPreProcessing() ? postTransform(in, off, len)
                              : preTransform(in, off, len));
  }

  private byte[] preTransform(byte[] in, int off, int len)
      throws TransformerException
  {
    byte[] result = updateDelegate(in, off, len);
    result = tail.update(result);
    return result;
  }

  private byte[] postTransform(byte[] in, int off, int len)
      throws TransformerException
  {
    byte[] result = tail.update(in, off, len);
    result = updateDelegate(result, 0, result.length);
    return result;
  }

  private byte[] lastForwardUpdate() throws TransformerException
  {
    return (isPreProcessing() ? preLastTransform() : postLastTransform());
  }

  private byte[] lastInverseUpdate() throws TransformerException
  {
    return (isPreProcessing() ? postLastTransform() : preLastTransform());
  }

  private byte[] preLastTransform() throws TransformerException
  {
    byte[] result = lastUpdateDelegate();
    result = tail.lastUpdate(result);
    return result;
  }

  private byte[] postLastTransform() throws TransformerException
  {
    byte[] result = tail.lastUpdate();
    result = updateDelegate(result, 0, result.length);
    byte[] rest = lastUpdateDelegate();
    if (rest.length > 0)
      {
        byte[] newResult = new byte[result.length + rest.length];
        System.arraycopy(result, 0, newResult, 0, result.length);
        System.arraycopy(rest, 0, newResult, result.length, rest.length);
        result = newResult;
      }
    return result;
  }

  abstract void initDelegate(Map attributes) throws TransformerException;

  abstract int delegateBlockSize();

  abstract void resetDelegate();

  abstract byte[] updateDelegate(byte[] in, int off, int len)
      throws TransformerException;

  abstract byte[] lastUpdateDelegate() throws TransformerException;
}