/*
 * CompressedOutputStream.java
 * Copyright (C) 2003 The Free Software Foundation
 * 
 * This file is part of GNU inetlib, a library.
 * 
 * GNU inetlib 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.
 * 
 * GNU inetlib 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 library; 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
 * obliged to do so.  If you do not wish to do so, delete this
 * exception statement from your version.
 */

package gnu.inet.ftp;

import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.OutputStream;

/**
 * A DTP output stream that implements the FTP compressed transfer mode.
 *
 * @author <a href='mailto:dog@gnu.org'>Chris Burdess</a>
 */
class CompressedOutputStream
  extends DTPOutputStream
{

  static final byte RECORD = -128;      // 0x80
  static final byte EOF = 64;   // 0x40

  CompressedOutputStream(DTP dtp, OutputStream out)
  {
    super(dtp, out);
  }
  
  /**
   * Just one byte cannot be compressed.
   * It takes 5 bytes to transmit - hardly very compressed!
   */
  public void write(int c)
    throws IOException
  {
    if (transferComplete)
      {
        return;
      }
    byte[] buf = new byte[]
      {
        RECORD,                   /* record descriptor */
        0x00, 0x01,             /* one byte */
        0x01,                   /* one uncompressed byte */
        (byte) c                /* the byte */
      };
    out.write(buf, 0, 5);
  }

  public void write(byte[] b)
    throws IOException
  {
    write(b, 0, b.length);
  }

  /**
   * The larger len is, the better.
   */
  public void write(byte[] b, int off, int len)
    throws IOException
  {
    if (transferComplete)
      {
        return;
      }
    byte[] buf = compress(b, off, len);
    len = buf.length;
    buf[0] = RECORD;            /* record descriptor */
    buf[1] = (byte) ((len & 0x00ff) >> 8);      /* high byte of bytecount */
    buf[2] = (byte) (len & 0xff00);     /* low byte of bytecount */
    out.write(buf, 0, len);
  }

  /**
   * Returns the compressed form of the given byte array.
   * The first 3 bytes are left free for header information.
   */
  byte[] compress(byte[] b, int off, int len)
  {
    byte[] buf = new byte[len];
    byte last = 0;
    int pos = 0, raw_count = 0, rep_count = 1;
    for (int i = off; i < len; i++)
      {
        byte c = b[i];
        if (i > off && c == last) // compress
          {
            if (raw_count > 0)      // flush raw bytes to buf
              {
                // need to add raw_count+1 bytes
                if (pos + (raw_count + 1) > buf.length)
                  {
                    buf = realloc(buf, len);
                  }
                pos = flush_raw(buf, pos, b, (i - raw_count) - 1,
                                raw_count);
                raw_count = 0;
              }
            rep_count++;            // keep looking for same byte
          }
        else
          {
            if (rep_count > 1)      // flush compressed bytes to buf
              {
                // need to add 2 bytes
                if (pos + 2 > buf.length)
                  {
                    buf = realloc(buf, len);
                  }
                pos = flush_compressed(buf, pos, rep_count, last);
                rep_count = 1;
              }
            raw_count++;            // keep looking for raw bytes
          }
        if (rep_count == 127)     // flush compressed bytes
          {
            // need to add 2 bytes
            if (pos + 2 > buf.length)
              {
                buf = realloc(buf, len);
              }
            pos = flush_compressed(buf, pos, rep_count, last);
            rep_count = 1;
          }
        if (raw_count == 127)     // flush raw bytes
          {
            // need to add raw_count+1 bytes
            if (pos + (raw_count + 1) > buf.length)
              {
                buf = realloc(buf, len);
              }
            pos = flush_raw(buf, pos, b, (i - raw_count), raw_count);
            raw_count = 0;
          }
        last = c;
      }
    if (rep_count > 1)          // flush compressed bytes
      {
        // need to add 2 bytes
        if (pos + 2 > buf.length)
          {
            buf = realloc(buf, len);
          }
        pos = flush_compressed(buf, pos, rep_count, last);
        rep_count = 1;
      }
    if (raw_count > 0)          // flush raw bytes
      {
        // need to add raw_count+1 bytes
        if (pos + (raw_count + 1) > buf.length)
          {
            buf = realloc(buf, len);
          }
        pos = flush_raw(buf, pos, b, (len - raw_count), raw_count);
        raw_count = 0;
      }
    byte[] ret = new byte[pos + 3];
    System.arraycopy(buf, 0, ret, 3, pos);
    return ret;
  }
  
  int flush_compressed(byte[] buf, int pos, int count, byte c)
  {
    buf[pos++] = (byte) (0x80 | count);
    buf[pos++] = c;
    return pos;
  }

  int flush_raw(byte[] buf, int pos, byte[] src, int off, int len)
  {
    buf[pos++] = (byte) len;
    System.arraycopy(src, off, buf, pos, len);
    return pos + len;
  }

  byte[] realloc(byte[] buf, int len)
  {
    byte[] ret = new byte[buf.length + len];
    System.arraycopy(buf, 0, ret, 0, buf.length);
    return ret;
  }

  public void close()
    throws IOException
  {
    byte[] buf = new byte[]
      {
        EOF,                      /* eof descriptor */
        0x00, 0x00              /* no bytes */
      };
    out.write(buf, 0, 3);
    out.close();
  }

}