//
// HuffmanCodec.java
//

/*
OME Bio-Formats package for reading and converting biological file formats.
Copyright (C) 2005-@year@ UW-Madison LOCI and Glencoe Software, Inc.

This program 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.

This program 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; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/

package loci.formats.codec;

import java.io.IOException;
import java.util.HashMap;

import loci.common.RandomAccessInputStream;
import loci.formats.FormatException;
import loci.formats.UnsupportedCompressionException;

/**
 * This class implements Huffman decoding.
 *
 * <dl><dt><b>Source code:</b></dt>
 * <dd><a href="http://trac.openmicroscopy.org.uk/ome/browser/bioformats.git/components/bio-formats/src/loci/formats/codec/HuffmanCodec.java">Trac</a>,
 * <a href="http://git.openmicroscopy.org/?p=bioformats.git;a=blob;f=components/bio-formats/src/loci/formats/codec/HuffmanCodec.java;hb=HEAD">Gitweb</a></dd></dl>
 *
 * @author Melissa Linkert melissa at glencoesoftware.com
 */
public class HuffmanCodec extends BaseCodec {

  // -- Constants --

  private static final int LEAVES_OFFSET = 16;

  // -- Fields --

  private int leafCounter;

  private HashMap<short[], Decoder> cachedDecoders =
    new HashMap<short[], Decoder>();

  // -- Codec API methods --

  /* @see Codec#compress(byte[], CodecOptions) */
  public byte[] compress(byte[] data, CodecOptions options)
    throws FormatException
  {
    throw new UnsupportedCompressionException(
      "Huffman encoding not currently supported");
  }

  /**
   * The CodecOptions parameter must be an instance of
   * {@link HuffmanCodecOptions}, and should have the following fields set:
   *   {@link HuffmanCodecOptions#table table}
   *   {@link CodecOptions#bitsPerSample bitsPerSample}
   *   {@link CodecOptions#maxBytes maxBytes}
   *
   * @see Codec#decompress(RandomAccessInputStream, CodecOptions)
   */
  public byte[] decompress(RandomAccessInputStream in, CodecOptions options)
    throws FormatException, IOException
  {
    if (in == null) 
      throw new IllegalArgumentException("No data to decompress.");
    if (options == null || !(options instanceof HuffmanCodecOptions)) {
      throw new FormatException("Options must be an instance of " +
        "loci.formats.codec.HuffmanCodecOptions.");
    }

    HuffmanCodecOptions huffman = (HuffmanCodecOptions) options;
    byte[] pix = new byte[huffman.maxBytes];
    in.read(pix);

    BitBuffer bb = new BitBuffer(pix);

    int nSamples = (huffman.maxBytes * 8) / huffman.bitsPerSample;
    int bytesPerSample = huffman.bitsPerSample / 8;
    if ((huffman.bitsPerSample % 8) != 0) bytesPerSample++;

    BitWriter out = new BitWriter();

    for (int i=0; i<nSamples; i++) {
      int sample = getSample(bb, options);
      out.write(sample, bytesPerSample * 8);
    }

    return out.toByteArray();
  }

  // -- HuffmanCodec API methods --

  public int getSample(BitBuffer bb, CodecOptions options)
    throws FormatException
  {
    if (bb == null) {
      throw new IllegalArgumentException("No data to handle.");
    }
    if (options == null || !(options instanceof HuffmanCodecOptions)) {
      throw new FormatException("Options must be an instance of " +
        "loci.formats.codec.HuffmanCodecOptions.");
    }

    HuffmanCodecOptions huffman = (HuffmanCodecOptions) options;
    Decoder decoder = cachedDecoders.get(huffman.table);
    if (decoder == null) {
      decoder = new Decoder(huffman.table);
      cachedDecoders.put(huffman.table, decoder);
    }

    int bitCount = decoder.decode(bb);
    if (bitCount < 0) bitCount = 0;
    int v = bb.getBits(bitCount) & ((int) Math.pow(2, bitCount) - 1);
    if ((v & (1 << (bitCount - 1))) == 0) {
      v -= (1 << bitCount) - 1;
    }

    return v;
  }

  // -- Helper class --

  class Decoder {
    public Decoder[] branch = new Decoder[2];
    private int leafValue = -1;

    public Decoder() { }

    public Decoder(short[] source) {
      leafCounter = 0;
      createDecoder(this, source, 0, 0);
    }

    private Decoder createDecoder(short[] source, int start, int level) {
      Decoder dest = new Decoder();
      createDecoder(dest, source, start, level);
      return dest;
    }

    private void createDecoder(Decoder dest, short[] source, int start,
      int level)
    {
      int next = 0;
      int i = 0;
      while (i <= leafCounter && next < LEAVES_OFFSET) {
        i += source[start + next++] & 0xff;
      }

      if (level < next && next < LEAVES_OFFSET) {
        dest.branch[0] = createDecoder(source, start, level + 1);
        dest.branch[1] = createDecoder(source, start, level + 1);
      }
      else {
        i = start + LEAVES_OFFSET + leafCounter++;
        if (i < source.length) {
          dest.leafValue = source[i] & 0xff;
        }
      }
    }

    public int decode(BitBuffer bb) {
      Decoder d = this;
      while (d.branch[0] != null) {
        int v = bb.getBits(1);
        if (v < 0) break; // eof
        d = d.branch[v];
      }
      return d.leafValue;
    }

  }

}