

import java.util.zip.*;
import java.io.OutputStream;
import java.io.IOException;

/**
 * This class essentially copies sources of original GZIPOutputStream,
 * just adds ability to pass in desired compression level into constructor
 */
public class GZIPOutputStreamEx extends DeflaterOutputStream
{
	/**
	 * CRC-32 of uncompressed data.
	 */
	protected CRC32 crc = new CRC32();
	
    /*
     * GZIP header magic number.
     */
	private final static int GZIP_MAGIC = 0x8b1f;
	
	/**
	 * Creates a new output stream with the specified buffer size.
	 * @param out the output stream
	 * @param size the output buffer size
	 * @exception IOException If an I/O error has occurred.
	 * @exception IllegalArgumentException if size is <= 0
	 */
	public GZIPOutputStreamEx(OutputStream out, int size, int compression) throws IOException
	{
		super(out, new Deflater(compression, true), size);
		writeHeader();
		crc.reset();
	}
	
	/**
	 * Creates a new output stream with a default buffer size.
	 * @param out the output stream
	 * @exception IOException If an I/O error has occurred.
	 */
	public GZIPOutputStreamEx(OutputStream out, int compression) throws IOException
	{
		this(out, 512, compression);
	}
	
	/**
	 * Writes array of bytes to the compressed output stream. This method
	 * will block until all the bytes are written.
	 * @param buf the data to be written
	 * @param off the start offset of the data
	 * @param len the length of the data
	 * @exception IOException If an I/O error has occurred.
	 */
	public synchronized void write(byte[] buf, int off, int len)
	throws IOException
	{
		super.write(buf, off, len);
		crc.update(buf, off, len);
	}
	
	/**
	 * Finishes writing compressed data to the output stream without closing
	 * the underlying stream. Use this method when applying multiple filters
	 * in succession to the same output stream.
	 * @exception IOException if an I/O error has occurred
	 */
	public void finish() throws IOException
	{
		if (!def.finished())
		{
			def.finish();
			while (!def.finished())
			{
				deflate();
			}
			writeTrailer();
		}
	}
	
	/**
	 * Writes remaining compressed data to the output stream and closes the
	 * underlying stream.
	 * @exception IOException if an I/O error has occurred
	 */
	public void close() throws IOException
	{
		finish();
		out.close();
	}
	
    /*
     * Writes GZIP member header.
     */
	private void writeHeader() throws IOException
	{
		writeShort(GZIP_MAGIC);	    // Magic number
		out.write(def.DEFLATED);    // Compression method (CM)
		out.write(0);		    // Flags (FLG)
		writeInt(0);		    // Modification time (MTIME)
		out.write(0);		    // Extra flags (XFL)
		out.write(0);		    // Operating system (OS)
	}
	
    /*
     * Writes GZIP member trailer.
     */
	private void writeTrailer() throws IOException
	{
		writeInt((int)crc.getValue());  // CRC-32 of uncompressed data
		writeInt(def.getTotalIn());	// Number of uncompressed bytes
	}
	
    /*
     * Writes integer in Intel byte order.
     */
	private void writeInt(int i) throws IOException
	{
		writeShort(i & 0xffff);
		writeShort((i >> 16) & 0xffff);
	}
	
    /*
     * Writes short integer in Intel byte order.
     */
	private void writeShort(int s) throws IOException
	{
		out.write(s & 0xff);
		out.write((s >> 8) & 0xff);
	}
}