/*
    * Copyright (C) 2010, Google Inc.
    * and other copyright owners as documented in the project's IP log.
    *
    * This program and the accompanying materials are made available
    * under the terms of the Eclipse Distribution License v1.0 which
    * accompanies this distribution, is reproduced below, and is
    * available at http://www.eclipse.org/org/documents/edl-v10.php
    *
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   * without modification, are permitted provided that the following
   * conditions are met:
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   *   notice, this list of conditions and the following disclaimer.
   *
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   *   disclaimer in the documentation and/or other materials provided
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   *   names of its contributors may be used to endorse or promote
   *   products derived from this software without specific prior
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   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
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  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"); //$NON-NLS-1$ //$NON-NLS-2$
  		}
  
  		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();
 		}
 	}
 }