/*
    * Copyright (C) 2008-2010, Google Inc. and others
    *
    * This program and the accompanying materials are made available under the
    * terms of the Eclipse Distribution License v. 1.0 which is available at
    * https://www.eclipse.org/org/documents/edl-v10.php.
    *
    * SPDX-License-Identifier: BSD-3-Clause
    */
  
  package org.eclipse.jgit.transport;
  
  import java.io.IOException;
  import java.io.OutputStream;
  import java.text.MessageFormat;
  
  import org.eclipse.jgit.internal.JGitText;
  
  /**
   * Multiplexes data and progress messages.
   * <p>
   * This stream is buffered at packet sizes, so the caller doesn't need to wrap
   * it in yet another buffered stream.
   *
   * @since 2.0
   */
  public class SideBandOutputStream extends OutputStream {
  	/** Channel used for pack data. */
  	public static final int CH_DATA = SideBandInputStream.CH_DATA;
  
  	/** Channel used for progress messages. */
  	public static final int CH_PROGRESS = SideBandInputStream.CH_PROGRESS;
  
  	/** Channel used for error messages. */
  	public static final int CH_ERROR = SideBandInputStream.CH_ERROR;
  
  	/** Default buffer size for a small amount of data. */
  	public static final int SMALL_BUF = 1000;
  
  	/** Maximum buffer size for a single packet of sideband data. */
  	public static final int MAX_BUF = 65520;
  
  	static final int HDR_SIZE = 5;
  
  	private final OutputStream out;
  
  	private final byte[] buffer;
  
  	/**
  	 * Number of bytes in {@link #buffer} that are valid data.
  	 * <p>
  	 * Initialized to {@link #HDR_SIZE} if there is no application data in the
  	 * buffer, as the packet header always appears at the start of the buffer.
  	 */
  	private int cnt;
  
  	/**
  	 * Create a new stream to write side band packets.
  	 *
  	 * @param chan
  	 *            channel number to prefix all packets with, so the remote side
  	 *            can demultiplex the stream and get back the original data.
  	 *            Must be in the range [1, 255].
  	 * @param sz
  	 *            maximum size of a data packet within the stream. The remote
  	 *            side needs to agree to the packet size to prevent buffer
  	 *            overflows. Must be in the range [HDR_SIZE + 1, MAX_BUF).
  	 * @param os
  	 *            stream that the packets are written onto. This stream should
  	 *            be attached to a SideBandInputStream on the remote side.
  	 */
  	public SideBandOutputStream(int chan, int sz, OutputStream os) {
  		if (chan <= 0 || chan > 255)
  			throw new IllegalArgumentException(MessageFormat.format(
  					JGitText.get().channelMustBeInRange1_255,
  					Integer.valueOf(chan)));
  		if (sz <= HDR_SIZE)
  			throw new IllegalArgumentException(MessageFormat.format(
  					JGitText.get().packetSizeMustBeAtLeast,
  					Integer.valueOf(sz), Integer.valueOf(HDR_SIZE)));
  		else if (MAX_BUF < sz)
  			throw new IllegalArgumentException(MessageFormat.format(
  					JGitText.get().packetSizeMustBeAtMost, Integer.valueOf(sz),
  					Integer.valueOf(MAX_BUF)));
  
  		out = os;
  		buffer = new byte[sz];
  		buffer[4] = (byte) chan;
  		cnt = HDR_SIZE;
  	}
  
  	void flushBuffer() throws IOException {
  		if (HDR_SIZE < cnt)
  			writeBuffer();
  	}
  
  	/** {@inheritDoc} */
  	@Override
  	public void flush() throws IOException {
 		flushBuffer();
 		out.flush();
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public void write(byte[] b, int off, int len) throws IOException {
 		while (0 < len) {
 			int capacity = buffer.length - cnt;
 			if (cnt == HDR_SIZE && capacity < len) {
 				// Our block to write is bigger than the packet size,
 				// stream it out as-is to avoid unnecessary copies.
 				PacketLineOut.formatLength(buffer, buffer.length);
 				out.write(buffer, 0, HDR_SIZE);
 				out.write(b, off, capacity);
 				off += capacity;
 				len -= capacity;
 
 			} else {
 				if (capacity == 0)
 					writeBuffer();
 
 				int n = Math.min(len, capacity);
 				System.arraycopy(b, off, buffer, cnt, n);
 				cnt += n;
 				off += n;
 				len -= n;
 			}
 		}
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public void write(int b) throws IOException {
 		if (cnt == buffer.length)
 			writeBuffer();
 		buffer[cnt++] = (byte) b;
 	}
 
 	private void writeBuffer() throws IOException {
 		PacketLineOut.formatLength(buffer, cnt);
 		out.write(buffer, 0, cnt);
 		cnt = HDR_SIZE;
 	}
 }