/*
    * Copyright (C) 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.pgm.debug;
  
  import java.io.ByteArrayInputStream;
  import java.io.ByteArrayOutputStream;
  import java.io.IOException;
  import java.util.Collections;
  import java.util.zip.InflaterInputStream;
  
  import org.eclipse.jgit.errors.MissingObjectException;
  import org.eclipse.jgit.errors.StoredObjectRepresentationNotAvailableException;
  import org.eclipse.jgit.internal.storage.pack.BinaryDelta;
  import org.eclipse.jgit.internal.storage.pack.ObjectReuseAsIs;
  import org.eclipse.jgit.internal.storage.pack.ObjectToPack;
  import org.eclipse.jgit.internal.storage.pack.PackOutputStream;
  import org.eclipse.jgit.internal.storage.pack.PackWriter;
  import org.eclipse.jgit.internal.storage.pack.StoredObjectRepresentation;
  import org.eclipse.jgit.lib.NullProgressMonitor;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.ObjectReader;
  import org.eclipse.jgit.pgm.Command;
  import org.eclipse.jgit.pgm.TextBuiltin;
  import org.eclipse.jgit.revwalk.RevObject;
  import org.eclipse.jgit.revwalk.RevWalk;
  import org.eclipse.jgit.util.TemporaryBuffer;
  import org.kohsuke.args4j.Argument;
  
  @Command(usage = "usage_ShowPackDelta")
  class ShowPackDelta extends TextBuiltin {
  	@Argument(index = 0)
  	private ObjectId objectId;
  
  	/** {@inheritDoc} */
  	@Override
  	protected void run() throws Exception {
  		ObjectReader reader = db.newObjectReader();
  		RevObject obj;
  		try (RevWalk rw = new RevWalk(reader)) {
  			obj = rw.parseAny(objectId);
  		}
  		byte[] delta = getDelta(reader, obj);
  
  		// We're crossing our fingers that this will be a delta. Double
  		// check the size field in the header, it should match.
  		//
  		long size = reader.getObjectSize(obj, obj.getType());
  		try {
  			if (BinaryDelta.getResultSize(delta) != size)
  				throw die("Object " + obj.name() + " is not a delta"); //$NON-NLS-1$ //$NON-NLS-2$
  		} catch (ArrayIndexOutOfBoundsException bad) {
  			throw die("Object " + obj.name() + " is not a delta", bad); //$NON-NLS-1$ //$NON-NLS-2$
  		}
  
  		outw.println(BinaryDelta.format(delta));
  	}
  
  	private static byte[] getDelta(ObjectReader reader, RevObject obj)
  			throws IOException, MissingObjectException,
  			StoredObjectRepresentationNotAvailableException {
  		ObjectReuseAsIs asis = (ObjectReuseAsIs) reader;
  		ObjectToPack target = asis.newObjectToPack(obj, obj.getType());
  
  		PackWriter pw = new PackWriter(reader) {
  			@Override
  			public void select(ObjectToPack otp, StoredObjectRepresentation next) {
  				otp.select(next);
  			}
  		};
  
  		ByteArrayOutputStream buf = new ByteArrayOutputStream();
  		asis.selectObjectRepresentation(pw, NullProgressMonitor.INSTANCE,
  				Collections.singleton(target));
  		asis.copyObjectAsIs(new PackOutputStream(NullProgressMonitor.INSTANCE,
  				buf, pw), target, true);
  
  		// At this point the object header has no delta information,
  		// because it was output as though it were a whole object.
  		// Skip over the header and inflate.
  		//
  		byte[] bufArray = buf.toByteArray();
  		int ptr = 0;
  		while ((bufArray[ptr] & 0x80) != 0)
  			ptr++;
  		ptr++;
  
  		try (TemporaryBuffer.Heap raw = new TemporaryBuffer.Heap(
  				bufArray.length);
  				InflaterInputStream inf = new InflaterInputStream(
  						new ByteArrayInputStream(bufArray, ptr,
  								bufArray.length))) {
 			raw.copy(inf);
 			return raw.toByteArray();
 		}
 	}
 }