/*
    * Copyright (C) 2008-2009, Google Inc.
    * Copyright (C) 2008, Marek Zawirski <marek.zawirski@gmail.com> 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.internal.storage.pack;
  
  import static org.eclipse.jgit.lib.Constants.OBJ_OFS_DELTA;
  import static org.eclipse.jgit.lib.Constants.OBJ_REF_DELTA;
  import static org.eclipse.jgit.lib.Constants.PACK_SIGNATURE;
  
  import java.io.IOException;
  import java.io.OutputStream;
  
  import org.eclipse.jgit.internal.storage.io.CancellableDigestOutputStream;
  import org.eclipse.jgit.lib.ProgressMonitor;
  import org.eclipse.jgit.util.NB;
  
  /**
   * Custom output stream to support
   * {@link org.eclipse.jgit.internal.storage.pack.PackWriter}.
   */
  public final class PackOutputStream extends CancellableDigestOutputStream {
  
  	private final PackWriter packWriter;
  
  	private final byte[] headerBuffer = new byte[32];
  
  	private final byte[] copyBuffer = new byte[64 << 10];
  
  	private boolean ofsDelta;
  
  	/**
  	 * Initialize a pack output stream.
  	 * <p>
  	 * This constructor is exposed to support debugging the JGit library only.
  	 * Application or storage level code should not create a PackOutputStream,
  	 * instead use {@link org.eclipse.jgit.internal.storage.pack.PackWriter},
  	 * and let the writer create the stream.
  	 *
  	 * @param writeMonitor
  	 *            monitor to update on object output progress.
  	 * @param out
  	 *            target stream to receive all object contents.
  	 * @param pw
  	 *            packer that is going to perform the output.
  	 */
  	public PackOutputStream(final ProgressMonitor writeMonitor,
  			final OutputStream out, final PackWriter pw) {
  		super(writeMonitor, out);
  		this.packWriter = pw;
  	}
  
  	final void writeFileHeader(int version, long objectCount)
  			throws IOException {
  		System.arraycopy(PACK_SIGNATURE, 0, headerBuffer, 0, 4);
  		NB.encodeInt32(headerBuffer, 4, version);
  		NB.encodeInt32(headerBuffer, 8, (int) objectCount);
  		write(headerBuffer, 0, 12);
  		ofsDelta = packWriter.isDeltaBaseAsOffset();
  	}
  
  	/**
  	 * Write one object.
  	 *
  	 * If the object was already written, this method does nothing and returns
  	 * quickly. This case occurs whenever an object was written out of order in
  	 * order to ensure the delta base occurred before the object that needs it.
  	 *
  	 * @param otp
  	 *            the object to write.
  	 * @throws java.io.IOException
  	 *             the object cannot be read from the object reader, or the
  	 *             output stream is no longer accepting output. Caller must
  	 *             examine the type of exception and possibly its message to
  	 *             distinguish between these cases.
  	 */
  	public final void writeObject(ObjectToPack otp) throws IOException {
  		packWriter.writeObject(this, otp);
  	}
  
  	/**
  	 * Commits the object header onto the stream.
  	 * <p>
  	 * Once the header has been written, the object representation must be fully
  	 * output, or packing must abort abnormally.
  	 *
  	 * @param otp
  	 *            the object to pack. Header information is obtained.
  	 * @param rawLength
  	 *            number of bytes of the inflated content. For an object that is
  	 *            in whole object format, this is the same as the object size.
  	 *            For an object that is in a delta format, this is the size of
 	 *            the inflated delta instruction stream.
 	 * @throws java.io.IOException
 	 *             the underlying stream refused to accept the header.
 	 */
 	@SuppressWarnings("ShortCircuitBoolean")
 	public final void writeHeader(ObjectToPack otp, long rawLength)
 			throws IOException {
 		ObjectToPack b = otp.getDeltaBase();
 		if (b != null && (b.isWritten() & ofsDelta)) { // Non-short-circuit logic is intentional
 			int n = objectHeader(rawLength, OBJ_OFS_DELTA, headerBuffer);
 			n = ofsDelta(length() - b.getOffset(), headerBuffer, n);
 			write(headerBuffer, 0, n);
 		} else if (otp.isDeltaRepresentation()) {
 			int n = objectHeader(rawLength, OBJ_REF_DELTA, headerBuffer);
 			otp.getDeltaBaseId().copyRawTo(headerBuffer, n);
 			write(headerBuffer, 0, n + 20);
 		} else {
 			int n = objectHeader(rawLength, otp.getType(), headerBuffer);
 			write(headerBuffer, 0, n);
 		}
 	}
 
 	private static final int objectHeader(long len, int type, byte[] buf) {
 		byte b = (byte) ((type << 4) | (len & 0x0F));
 		int n = 0;
 		for (len >>>= 4; len != 0; len >>>= 7) {
 			buf[n++] = (byte) (0x80 | b);
 			b = (byte) (len & 0x7F);
 		}
 		buf[n++] = b;
 		return n;
 	}
 
 	private static final int ofsDelta(long diff, byte[] buf, int p) {
 		p += ofsDeltaVarIntLength(diff);
 		int n = p;
 		buf[--n] = (byte) (diff & 0x7F);
 		while ((diff >>>= 7) != 0)
 			buf[--n] = (byte) (0x80 | (--diff & 0x7F));
 		return p;
 	}
 
 	private static final int ofsDeltaVarIntLength(long v) {
 		int n = 1;
 		for (; (v >>>= 7) != 0; n++)
 			--v;
 		return n;
 	}
 
 	/**
 	 * Get a temporary buffer writers can use to copy data with.
 	 *
 	 * @return a temporary buffer writers can use to copy data with.
 	 */
 	public final byte[] getCopyBuffer() {
 		return copyBuffer;
 	}
 
 	void endObject() {
 		getWriteMonitor().update(1);
 	}
 }