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);
        }
}