/*
    * Copyright (C) 2011, 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
    *
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or
   * without modification, are permitted provided that the following
   * conditions are met:
   *
   * - Redistributions of source code must retain the above copyright
   *   notice, this list of conditions and the following disclaimer.
   *
   * - Redistributions in binary form must reproduce the above
   *   copyright notice, this list of conditions and the following
   *   disclaimer in the documentation and/or other materials provided
   *   with the distribution.
   *
   * - Neither the name of the Eclipse Foundation, Inc. nor the
   *   names of its contributors may be used to endorse or promote
   *   products derived from this software without specific prior
   *   written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
   * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
   * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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   * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
   * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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  package org.eclipse.jgit.blame;
  
  import static org.eclipse.jgit.lib.Constants.OBJ_BLOB;
  import static org.eclipse.jgit.lib.FileMode.TYPE_FILE;
  import static org.eclipse.jgit.lib.FileMode.TYPE_MASK;
  
  import java.io.IOException;
  import java.util.Collection;
  import java.util.Collections;
  
  import org.eclipse.jgit.blame.Candidate.BlobCandidate;
  import org.eclipse.jgit.blame.Candidate.ReverseCandidate;
  import org.eclipse.jgit.blame.ReverseWalk.ReverseCommit;
  import org.eclipse.jgit.diff.DiffAlgorithm;
  import org.eclipse.jgit.diff.DiffEntry;
  import org.eclipse.jgit.diff.DiffEntry.ChangeType;
  import org.eclipse.jgit.diff.EditList;
  import org.eclipse.jgit.diff.HistogramDiff;
  import org.eclipse.jgit.diff.RawText;
  import org.eclipse.jgit.diff.RawTextComparator;
  import org.eclipse.jgit.diff.RenameDetector;
  import org.eclipse.jgit.internal.JGitText;
  import org.eclipse.jgit.lib.AnyObjectId;
  import org.eclipse.jgit.lib.MutableObjectId;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.ObjectLoader;
  import org.eclipse.jgit.lib.ObjectReader;
  import org.eclipse.jgit.lib.PersonIdent;
  import org.eclipse.jgit.lib.Repository;
  import org.eclipse.jgit.revwalk.RevCommit;
  import org.eclipse.jgit.revwalk.RevFlag;
  import org.eclipse.jgit.revwalk.RevWalk;
  import org.eclipse.jgit.treewalk.TreeWalk;
  import org.eclipse.jgit.treewalk.filter.PathFilter;
  import org.eclipse.jgit.treewalk.filter.TreeFilter;
  
  /**
   * Generate author information for lines based on a provided file.
   * <p>
   * Applications that want a simple one-shot computation of blame for a file
   * should use {@link #computeBlameResult()} to prepare the entire result in one
   * method call. This may block for significant time as the history of the
   * repository must be traversed until information is gathered for every line.
   * <p>
   * Applications that want more incremental update behavior may use either the
   * raw {@link #next()} streaming approach supported by this class, or construct
   * a {@link BlameResult} using {@link BlameResult#create(BlameGenerator)} and
   * incrementally construct the result with {@link BlameResult#computeNext()}.
   * <p>
   * This class is not thread-safe.
   * <p>
   * An instance of BlameGenerator can only be used once. To blame multiple files
   * the application must create a new BlameGenerator.
   * <p>
   * During blame processing there are two files involved:
   * <ul>
  * <li>result - The file whose lines are being examined. This is the revision
  * the user is trying to view blame/annotation information alongside of.</li>
  * <li>source - The file that was blamed with supplying one or more lines of
  * data into result. The source may be a different file path (due to copy or
  * rename). Source line numbers may differ from result line numbers due to lines
  * being added/removed in intermediate revisions.</li>
  * </ul>
  * <p>
  * The blame algorithm is implemented by initially assigning responsibility for
  * all lines of the result to the starting commit. A difference against the
  * commit's ancestor is computed, and responsibility is passed to the ancestor
  * commit for any lines that are common. The starting commit is blamed only for
  * the lines that do not appear in the ancestor, if any. The loop repeats using
  * the ancestor, until there are no more lines to acquire information on, or the
  * file's creation point is discovered in history.
  */
 public class BlameGenerator implements AutoCloseable {
 	private final Repository repository;
 
 	private final PathFilter resultPath;
 
 	private final MutableObjectId idBuf;
 
 	/** Revision pool used to acquire commits from. */
 	private RevWalk revPool;
 
 	/** Indicates the commit was put into the queue at least once. */
 	private RevFlag SEEN;
 
 	private ObjectReader reader;
 
 	private TreeWalk treeWalk;
 
 	private DiffAlgorithm diffAlgorithm = new HistogramDiff();
 
 	private RawTextComparator textComparator = RawTextComparator.DEFAULT;
 
 	private RenameDetector renameDetector;
 
 	/** Potential candidates, sorted by commit time descending. */
 	private Candidate queue;
 
 	/** Number of lines that still need to be discovered. */
 	private int remaining;
 
 	/** Blame is currently assigned to this source. */
 	private Candidate outCandidate;
 	private Region outRegion;
 
 	/**
 	 * Create a blame generator for the repository and path (relative to
 	 * repository)
 	 *
 	 * @param repository
 	 *            repository to access revision data from.
 	 * @param path
 	 *            initial path of the file to start scanning (relative to the
 	 *            repository).
 	 */
 	public BlameGenerator(Repository repository, String path) {
 		this.repository = repository;
 		this.resultPath = PathFilter.create(path);
 
 		idBuf = new MutableObjectId();
 		setFollowFileRenames(true);
 		initRevPool(false);
 
 		remaining = -1;
 	}
 
 	private void initRevPool(boolean reverse) {
 		if (queue != null)
 			throw new IllegalStateException();
 
 		if (revPool != null)
 			revPool.close();
 
 		if (reverse)
 			revPool = new ReverseWalk(getRepository());
 		else
 			revPool = new RevWalk(getRepository());
 
 		SEEN = revPool.newFlag("SEEN"); //$NON-NLS-1$
 		reader = revPool.getObjectReader();
 		treeWalk = new TreeWalk(reader);
 		treeWalk.setRecursive(true);
 	}
 
 	/** @return repository being scanned for revision history. */
 	public Repository getRepository() {
 		return repository;
 	}
 
 	/** @return path file path being processed. */
 	public String getResultPath() {
 		return resultPath.getPath();
 	}
 
 	/**
 	 * Difference algorithm to use when comparing revisions.
 	 *
 	 * @param algorithm
 	 * @return {@code this}
 	 */
 	public BlameGenerator setDiffAlgorithm(DiffAlgorithm algorithm) {
 		diffAlgorithm = algorithm;
 		return this;
 	}
 
 	/**
 	 * Text comparator to use when comparing revisions.
 	 *
 	 * @param comparator
 	 * @return {@code this}
 	 */
 	public BlameGenerator setTextComparator(RawTextComparator comparator) {
 		textComparator = comparator;
 		return this;
 	}
 
 	/**
 	 * Enable (or disable) following file renames, on by default.
 	 * <p>
 	 * If true renames are followed using the standard FollowFilter behavior
 	 * used by RevWalk (which matches {@code git log --follow} in the C
 	 * implementation). This is not the same as copy/move detection as
 	 * implemented by the C implementation's of {@code git blame -M -C}.
 	 *
 	 * @param follow
 	 *            enable following.
 	 * @return {@code this}
 	 */
 	public BlameGenerator setFollowFileRenames(boolean follow) {
 		if (follow)
 			renameDetector = new RenameDetector(getRepository());
 		else
 			renameDetector = null;
 		return this;
 	}
 
 	/**
 	 * Obtain the RenameDetector if {@code setFollowFileRenames(true)}.
 	 *
 	 * @return the rename detector, allowing the application to configure its
 	 *         settings for rename score and breaking behavior.
 	 */
 	public RenameDetector getRenameDetector() {
 		return renameDetector;
 	}
 
 	/**
 	 * Push a candidate blob onto the generator's traversal stack.
 	 * <p>
 	 * Candidates should be pushed in history order from oldest-to-newest.
 	 * Applications should push the starting commit first, then the index
 	 * revision (if the index is interesting), and finally the working tree
 	 * copy (if the working tree is interesting).
 	 *
 	 * @param description
 	 *            description of the blob revision, such as "Working Tree".
 	 * @param contents
 	 *            contents of the file.
 	 * @return {@code this}
 	 * @throws IOException
 	 *             the repository cannot be read.
 	 */
 	public BlameGenerator push(String description, byte[] contents)
 			throws IOException {
 		return push(description, new RawText(contents));
 	}
 
 	/**
 	 * Push a candidate blob onto the generator's traversal stack.
 	 * <p>
 	 * Candidates should be pushed in history order from oldest-to-newest.
 	 * Applications should push the starting commit first, then the index
 	 * revision (if the index is interesting), and finally the working tree copy
 	 * (if the working tree is interesting).
 	 *
 	 * @param description
 	 *            description of the blob revision, such as "Working Tree".
 	 * @param contents
 	 *            contents of the file.
 	 * @return {@code this}
 	 * @throws IOException
 	 *             the repository cannot be read.
 	 */
 	public BlameGenerator push(String description, RawText contents)
 			throws IOException {
 		if (description == null)
 			description = JGitText.get().blameNotCommittedYet;
 		BlobCandidate c = new BlobCandidate(description, resultPath);
 		c.sourceText = contents;
 		c.regionList = new Region(0, 0, contents.size());
 		remaining = contents.size();
 		push(c);
 		return this;
 	}
 
 	/**
 	 * Push a candidate object onto the generator's traversal stack.
 	 * <p>
 	 * Candidates should be pushed in history order from oldest-to-newest.
 	 * Applications should push the starting commit first, then the index
 	 * revision (if the index is interesting), and finally the working tree copy
 	 * (if the working tree is interesting).
 	 *
 	 * @param description
 	 *            description of the blob revision, such as "Working Tree".
 	 * @param id
 	 *            may be a commit or a blob.
 	 * @return {@code this}
 	 * @throws IOException
 	 *             the repository cannot be read.
 	 */
 	public BlameGenerator push(String description, AnyObjectId id)
 			throws IOException {
 		ObjectLoader ldr = reader.open(id);
 		if (ldr.getType() == OBJ_BLOB) {
 			if (description == null)
 				description = JGitText.get().blameNotCommittedYet;
 			BlobCandidate c = new BlobCandidate(description, resultPath);
 			c.sourceBlob = id.toObjectId();
 			c.sourceText = new RawText(ldr.getCachedBytes(Integer.MAX_VALUE));
 			c.regionList = new Region(0, 0, c.sourceText.size());
 			remaining = c.sourceText.size();
 			push(c);
 			return this;
 		}
 
 		RevCommit commit = revPool.parseCommit(id);
 		if (!find(commit, resultPath))
 			return this;
 
 		Candidate c = new Candidate(commit, resultPath);
 		c.sourceBlob = idBuf.toObjectId();
 		c.loadText(reader);
 		c.regionList = new Region(0, 0, c.sourceText.size());
 		remaining = c.sourceText.size();
 		push(c);
 		return this;
 	}
 
 	/**
 	 * Configure the generator to compute reverse blame (history of deletes).
 	 * <p>
 	 * This method is expensive as it immediately runs a RevWalk over the
 	 * history spanning the expression {@code start..end} (end being more recent
 	 * than start) and then performs the equivalent operation as
 	 * {@link #push(String, AnyObjectId)} to begin blame traversal from the
 	 * commit named by {@code start} walking forwards through history until
 	 * {@code end} blaming line deletions.
 	 * <p>
 	 * A reverse blame may produce multiple sources for the same result line,
 	 * each of these is a descendant commit that removed the line, typically
 	 * this occurs when the same deletion appears in multiple side branches such
 	 * as due to a cherry-pick. Applications relying on reverse should use
 	 * {@link BlameResult} as it filters these duplicate sources and only
 	 * remembers the first (oldest) deletion.
 	 *
 	 * @param start
 	 *            oldest commit to traverse from. The result file will be loaded
 	 *            from this commit's tree.
 	 * @param end
 	 *            most recent commit to stop traversal at. Usually an active
 	 *            branch tip, tag, or HEAD.
 	 * @return {@code this}
 	 * @throws IOException
 	 *             the repository cannot be read.
 	 */
 	public BlameGenerator reverse(AnyObjectId start, AnyObjectId end)
 			throws IOException {
 		return reverse(start, Collections.singleton(end.toObjectId()));
 	}
 
 	/**
 	 * Configure the generator to compute reverse blame (history of deletes).
 	 * <p>
 	 * This method is expensive as it immediately runs a RevWalk over the
 	 * history spanning the expression {@code start..end} (end being more recent
 	 * than start) and then performs the equivalent operation as
 	 * {@link #push(String, AnyObjectId)} to begin blame traversal from the
 	 * commit named by {@code start} walking forwards through history until
 	 * {@code end} blaming line deletions.
 	 * <p>
 	 * A reverse blame may produce multiple sources for the same result line,
 	 * each of these is a descendant commit that removed the line, typically
 	 * this occurs when the same deletion appears in multiple side branches such
 	 * as due to a cherry-pick. Applications relying on reverse should use
 	 * {@link BlameResult} as it filters these duplicate sources and only
 	 * remembers the first (oldest) deletion.
 	 *
 	 * @param start
 	 *            oldest commit to traverse from. The result file will be loaded
 	 *            from this commit's tree.
 	 * @param end
 	 *            most recent commits to stop traversal at. Usually an active
 	 *            branch tip, tag, or HEAD.
 	 * @return {@code this}
 	 * @throws IOException
 	 *             the repository cannot be read.
 	 */
 	public BlameGenerator reverse(AnyObjectId start,
 			Collection<? extends ObjectId> end) throws IOException {
 		initRevPool(true);
 
 		ReverseCommit result = (ReverseCommit) revPool.parseCommit(start);
 		if (!find(result, resultPath))
 			return this;
 
 		revPool.markUninteresting(result);
 		for (ObjectId id : end)
 			revPool.markStart(revPool.parseCommit(id));
 
 		while (revPool.next() != null) {
 			// just pump the queue
 		}
 
 		ReverseCandidate c = new ReverseCandidate(result, resultPath);
 		c.sourceBlob = idBuf.toObjectId();
 		c.loadText(reader);
 		c.regionList = new Region(0, 0, c.sourceText.size());
 		remaining = c.sourceText.size();
 		push(c);
 		return this;
 	}
 
 	/**
 	 * Allocate a new RevFlag for use by the caller.
 	 *
 	 * @param name
 	 *            unique name of the flag in the blame context.
 	 * @return the newly allocated flag.
 	 * @since 3.4
 	 */
 	public RevFlag newFlag(String name) {
 		return revPool.newFlag(name);
 	}
 
 	/**
 	 * Execute the generator in a blocking fashion until all data is ready.
 	 *
 	 * @return the complete result. Null if no file exists for the given path.
 	 * @throws IOException
 	 *             the repository cannot be read.
 	 */
 	public BlameResult computeBlameResult() throws IOException {
 		try {
 			BlameResult r = BlameResult.create(this);
 			if (r != null)
 				r.computeAll();
 			return r;
 		} finally {
 			close();
 		}
 	}
 
 	/**
 	 * Step the blame algorithm one iteration.
 	 *
 	 * @return true if the generator has found a region's source. The getSource*
 	 *         and {@link #getResultStart()}, {@link #getResultEnd()} methods
 	 *         can be used to inspect the region found. False if there are no
 	 *         more regions to describe.
 	 * @throws IOException
 	 *             repository cannot be read.
 	 */
 	public boolean next() throws IOException {
 		// If there is a source still pending, produce the next region.
 		if (outRegion != null) {
 			Region r = outRegion;
 			remaining -= r.length;
 			if (r.next != null) {
 				outRegion = r.next;
 				return true;
 			}
 
 			if (outCandidate.queueNext != null)
 				return result(outCandidate.queueNext);
 
 			outCandidate = null;
 			outRegion = null;
 		}
 
 		// If there are no lines remaining, the entire result is done,
 		// even if there are revisions still available for the path.
 		if (remaining == 0)
 			return done();
 
 		for (;;) {
 			Candidate n = pop();
 			if (n == null)
 				return done();
 
 			int pCnt = n.getParentCount();
 			if (pCnt == 1) {
 				if (processOne(n))
 					return true;
 
 			} else if (1 < pCnt) {
 				if (processMerge(n))
 					return true;
 
 			} else if (n instanceof ReverseCandidate) {
 				// Do not generate a tip of a reverse. The region
 				// survives and should not appear to be deleted.
 
 			} else /* if (pCnt == 0) */{
 				// Root commit, with at least one surviving region.
 				// Assign the remaining blame here.
 				return result(n);
 			}
 		}
 	}
 
 	private boolean done() {
 		close();
 		return false;
 	}
 
 	private boolean result(Candidate n) throws IOException {
 		n.beginResult(revPool);
 		outCandidate = n;
 		outRegion = n.regionList;
 		return true;
 	}
 
 	private boolean reverseResult(Candidate parent, Candidate source)
 			throws IOException {
 		// On a reverse blame present the application the parent
 		// (as this is what did the removals), however the region
 		// list to enumerate is the source's surviving list.
 		Candidate res = parent.copy(parent.sourceCommit);
 		res.regionList = source.regionList;
 		return result(res);
 	}
 
 	private Candidate pop() {
 		Candidate n = queue;
 		if (n != null) {
 			queue = n.queueNext;
 			n.queueNext = null;
 		}
 		return n;
 	}
 
 	private void push(BlobCandidate toInsert) {
 		Candidate c = queue;
 		if (c != null) {
 			c.remove(SEEN); // will be pushed by toInsert
 			c.regionList = null;
 			toInsert.parent = c;
 		}
 		queue = toInsert;
 	}
 
 	private void push(Candidate toInsert) {
 		if (toInsert.has(SEEN)) {
 			// We have already added a Candidate for this commit to the queue,
 			// this can happen if the commit is a merge base for two or more
 			// parallel branches that were merged together.
 			//
 			// It is likely the candidate was not yet processed. The queue
 			// sorts descending by commit time and usually descendant commits
 			// have higher timestamps than the ancestors.
 			//
 			// Find the existing candidate and merge the new candidate's
 			// region list into it.
 			for (Candidate p = queue; p != null; p = p.queueNext) {
 				if (p.canMergeRegions(toInsert)) {
 					p.mergeRegions(toInsert);
 					return;
 				}
 			}
 		}
 		toInsert.add(SEEN);
 
 		// Insert into the queue using descending commit time, so
 		// the most recent commit will pop next.
 		int time = toInsert.getTime();
 		Candidate n = queue;
 		if (n == null || time >= n.getTime()) {
 			toInsert.queueNext = n;
 			queue = toInsert;
 			return;
 		}
 
 		for (Candidate p = n;; p = n) {
 			n = p.queueNext;
 			if (n == null || time >= n.getTime()) {
 				toInsert.queueNext = n;
 				p.queueNext = toInsert;
 				return;
 			}
 		}
 	}
 
 	private boolean processOne(Candidate n) throws IOException {
 		RevCommit parent = n.getParent(0);
 		if (parent == null)
 			return split(n.getNextCandidate(0), n);
 		revPool.parseHeaders(parent);
 
 		if (find(parent, n.sourcePath)) {
 			if (idBuf.equals(n.sourceBlob))
 				return blameEntireRegionOnParent(n, parent);
 			return splitBlameWithParent(n, parent);
 		}
 
 		if (n.sourceCommit == null)
 			return result(n);
 
 		DiffEntry r = findRename(parent, n.sourceCommit, n.sourcePath);
 		if (r == null)
 			return result(n);
 
 		if (0 == r.getOldId().prefixCompare(n.sourceBlob)) {
 			// A 100% rename without any content change can also
 			// skip directly to the parent.
 			n.sourceCommit = parent;
 			n.sourcePath = PathFilter.create(r.getOldPath());
 			push(n);
 			return false;
 		}
 
 		Candidate next = n.create(parent, PathFilter.create(r.getOldPath()));
 		next.sourceBlob = r.getOldId().toObjectId();
 		next.renameScore = r.getScore();
 		next.loadText(reader);
 		return split(next, n);
 	}
 
 	private boolean blameEntireRegionOnParent(Candidate n, RevCommit parent) {
 		// File was not modified, blame parent.
 		n.sourceCommit = parent;
 		push(n);
 		return false;
 	}
 
 	private boolean splitBlameWithParent(Candidate n, RevCommit parent)
 			throws IOException {
 		Candidate next = n.create(parent, n.sourcePath);
 		next.sourceBlob = idBuf.toObjectId();
 		next.loadText(reader);
 		return split(next, n);
 	}
 
 	private boolean split(Candidate parent, Candidate source)
 			throws IOException {
 		EditList editList = diffAlgorithm.diff(textComparator,
 				parent.sourceText, source.sourceText);
 		if (editList.isEmpty()) {
 			// Ignoring whitespace (or some other special comparator) can
 			// cause non-identical blobs to have an empty edit list. In
 			// a case like this push the parent alone.
 			parent.regionList = source.regionList;
 			push(parent);
 			return false;
 		}
 
 		parent.takeBlame(editList, source);
 		if (parent.regionList != null)
 			push(parent);
 		if (source.regionList != null) {
 			if (source instanceof ReverseCandidate)
 				return reverseResult(parent, source);
 			return result(source);
 		}
 		return false;
 	}
 
 	private boolean processMerge(Candidate n) throws IOException {
 		int pCnt = n.getParentCount();
 
 		// If any single parent exactly matches the merge, follow only
 		// that one parent through history.
 		ObjectId[] ids = null;
 		for (int pIdx = 0; pIdx < pCnt; pIdx++) {
 			RevCommit parent = n.getParent(pIdx);
 			revPool.parseHeaders(parent);
 			if (!find(parent, n.sourcePath))
 				continue;
 			if (!(n instanceof ReverseCandidate) && idBuf.equals(n.sourceBlob))
 				return blameEntireRegionOnParent(n, parent);
 			if (ids == null)
 				ids = new ObjectId[pCnt];
 			ids[pIdx] = idBuf.toObjectId();
 		}
 
 		// If rename detection is enabled, search for any relevant names.
 		DiffEntry[] renames = null;
 		if (renameDetector != null) {
 			renames = new DiffEntry[pCnt];
 			for (int pIdx = 0; pIdx < pCnt; pIdx++) {
 				RevCommit parent = n.getParent(pIdx);
 				if (ids != null && ids[pIdx] != null)
 					continue;
 
 				DiffEntry r = findRename(parent, n.sourceCommit, n.sourcePath);
 				if (r == null)
 					continue;
 
 				if (n instanceof ReverseCandidate) {
 					if (ids == null)
 						ids = new ObjectId[pCnt];
 					ids[pCnt] = r.getOldId().toObjectId();
 				} else if (0 == r.getOldId().prefixCompare(n.sourceBlob)) {
 					// A 100% rename without any content change can also
 					// skip directly to the parent. Note this bypasses an
 					// earlier parent that had the path (above) but did not
 					// have an exact content match. For performance reasons
 					// we choose to follow the one parent over trying to do
 					// possibly both parents.
 					n.sourcePath = PathFilter.create(r.getOldPath());
 					return blameEntireRegionOnParent(n, parent);
 				}
 
 				renames[pIdx] = r;
 			}
 		}
 
 		// Construct the candidate for each parent.
 		Candidate[] parents = new Candidate[pCnt];
 		for (int pIdx = 0; pIdx < pCnt; pIdx++) {
 			RevCommit parent = n.getParent(pIdx);
 
 			Candidate p;
 			if (renames != null && renames[pIdx] != null) {
 				p = n.create(parent,
 						PathFilter.create(renames[pIdx].getOldPath()));
 				p.renameScore = renames[pIdx].getScore();
 				p.sourceBlob = renames[pIdx].getOldId().toObjectId();
 			} else if (ids != null && ids[pIdx] != null) {
 				p = n.create(parent, n.sourcePath);
 				p.sourceBlob = ids[pIdx];
 			} else {
 				continue;
 			}
 
 			EditList editList;
 			if (n instanceof ReverseCandidate
 					&& p.sourceBlob.equals(n.sourceBlob)) {
 				// This special case happens on ReverseCandidate forks.
 				p.sourceText = n.sourceText;
 				editList = new EditList(0);
 			} else {
 				p.loadText(reader);
 				editList = diffAlgorithm.diff(textComparator,
 						p.sourceText, n.sourceText);
 			}
 
 			if (editList.isEmpty()) {
 				// Ignoring whitespace (or some other special comparator) can
 				// cause non-identical blobs to have an empty edit list. In
 				// a case like this push the parent alone.
 				if (n instanceof ReverseCandidate) {
 					parents[pIdx] = p;
 					continue;
 				}
 
 				p.regionList = n.regionList;
 				n.regionList = null;
 				parents[pIdx] = p;
 				break;
 			}
 
 			p.takeBlame(editList, n);
 
 			// Only remember this parent candidate if there is at least
 			// one region that was blamed on the parent.
 			if (p.regionList != null) {
 				// Reverse blame requires inverting the regions. This puts
 				// the regions the parent deleted from us into the parent,
 				// and retains the common regions to look at other parents
 				// for deletions.
 				if (n instanceof ReverseCandidate) {
 					Region r = p.regionList;
 					p.regionList = n.regionList;
 					n.regionList = r;
 				}
 
 				parents[pIdx] = p;
 			}
 		}
 
 		if (n instanceof ReverseCandidate) {
 			// On a reverse blame report all deletions found in the children,
 			// and pass on to them a copy of our region list.
 			Candidate resultHead = null;
 			Candidate resultTail = null;
 
 			for (int pIdx = 0; pIdx < pCnt; pIdx++) {
 				Candidate p = parents[pIdx];
 				if (p == null)
 					continue;
 
 				if (p.regionList != null) {
 					Candidate r = p.copy(p.sourceCommit);
 					if (resultTail != null) {
 						resultTail.queueNext = r;
 						resultTail = r;
 					} else {
 						resultHead = r;
 						resultTail = r;
 					}
 				}
 
 				if (n.regionList != null) {
 					p.regionList = n.regionList.deepCopy();
 					push(p);
 				}
 			}
 
 			if (resultHead != null)
 				return result(resultHead);
 			return false;
 		}
 
 		// Push any parents that are still candidates.
 		for (int pIdx = 0; pIdx < pCnt; pIdx++) {
 			if (parents[pIdx] != null)
 				push(parents[pIdx]);
 		}
 
 		if (n.regionList != null)
 			return result(n);
 		return false;
 	}
 
 	/**
 	 * Get the revision blamed for the current region.
 	 * <p>
 	 * The source commit may be null if the line was blamed to an uncommitted
 	 * revision, such as the working tree copy, or during a reverse blame if the
 	 * line survives to the end revision (e.g. the branch tip).
 	 *
 	 * @return current revision being blamed.
 	 */
 	public RevCommit getSourceCommit() {
 		return outCandidate.sourceCommit;
 	}
 
 	/** @return current author being blamed. */
 	public PersonIdent getSourceAuthor() {
 		return outCandidate.getAuthor();
 	}
 
 	/** @return current committer being blamed. */
 	public PersonIdent getSourceCommitter() {
 		RevCommit c = getSourceCommit();
 		return c != null ? c.getCommitterIdent() : null;
 	}
 
 	/** @return path of the file being blamed. */
 	public String getSourcePath() {
 		return outCandidate.sourcePath.getPath();
 	}
 
 	/** @return rename score if a rename occurred in {@link #getSourceCommit}. */
 	public int getRenameScore() {
 		return outCandidate.renameScore;
 	}
 
 	/**
 	 * @return first line of the source data that has been blamed for the
 	 *         current region. This is line number of where the region was added
 	 *         during {@link #getSourceCommit()} in file
 	 *         {@link #getSourcePath()}.
 	 */
 	public int getSourceStart() {
 		return outRegion.sourceStart;
 	}
 
 	/**
 	 * @return one past the range of the source data that has been blamed for
 	 *         the current region. This is line number of where the region was
 	 *         added during {@link #getSourceCommit()} in file
 	 *         {@link #getSourcePath()}.
 	 */
 	public int getSourceEnd() {
 		Region r = outRegion;
 		return r.sourceStart + r.length;
 	}
 
 	/**
 	 * @return first line of the result that {@link #getSourceCommit()} has been
 	 *         blamed for providing. Line numbers use 0 based indexing.
 	 */
 	public int getResultStart() {
 		return outRegion.resultStart;
 	}
 
 	/**
 	 * @return one past the range of the result that {@link #getSourceCommit()}
 	 *         has been blamed for providing. Line numbers use 0 based indexing.
 	 *         Because a source cannot be blamed for an empty region of the
 	 *         result, {@link #getResultEnd()} is always at least one larger
 	 *         than {@link #getResultStart()}.
 	 */
 	public int getResultEnd() {
 		Region r = outRegion;
 		return r.resultStart + r.length;
 	}
 
 	/**
 	 * @return number of lines in the current region being blamed to
 	 *         {@link #getSourceCommit()}. This is always the value of the
 	 *         expression {@code getResultEnd() - getResultStart()}, but also
 	 *         {@code getSourceEnd() - getSourceStart()}.
 	 */
 	public int getRegionLength() {
 		return outRegion.length;
 	}
 
 	/**
 	 * @return complete contents of the source file blamed for the current
 	 *         output region. This is the contents of {@link #getSourcePath()}
 	 *         within {@link #getSourceCommit()}. The source contents is
 	 *         temporarily available as an artifact of the blame algorithm. Most
 	 *         applications will want the result contents for display to users.
 	 */
 	public RawText getSourceContents() {
 		return outCandidate.sourceText;
 	}
 
 	/**
 	 * @return complete file contents of the result file blame is annotating.
 	 *         This value is accessible only after being configured and only
 	 *         immediately before the first call to {@link #next()}. Returns
 	 *         null if the path does not exist.
 	 * @throws IOException
 	 *             repository cannot be read.
 	 * @throws IllegalStateException
 	 *             {@link #next()} has already been invoked.
 	 */
 	public RawText getResultContents() throws IOException {
 		return queue != null ? queue.sourceText : null;
 	}
 
 	/**
 	 * Release the current blame session.
 	 *
 	 * @since 4.0
 	 */
 	@Override
 	public void close() {
 		revPool.close();
 		queue = null;
 		outCandidate = null;
 		outRegion = null;
 	}
 
 	private boolean find(RevCommit commit, PathFilter path) throws IOException {
 		treeWalk.setFilter(path);
 		treeWalk.reset(commit.getTree());
 		if (treeWalk.next() && isFile(treeWalk.getRawMode(0))) {
 			treeWalk.getObjectId(idBuf, 0);
 			return true;
 		}
 		return false;
 	}
 
 	private static final boolean isFile(int rawMode) {
 		return (rawMode & TYPE_MASK) == TYPE_FILE;
 	}
 
 	private DiffEntry findRename(RevCommit parent, RevCommit commit,
 			PathFilter path) throws IOException {
 		if (renameDetector == null)
 			return null;
 
 		treeWalk.setFilter(TreeFilter.ANY_DIFF);
 		treeWalk.reset(parent.getTree(), commit.getTree());
 		renameDetector.reset();
 		renameDetector.addAll(DiffEntry.scan(treeWalk));
 		for (DiffEntry ent : renameDetector.compute()) {
 			if (isRename(ent) && ent.getNewPath().equals(path.getPath()))
 				return ent;
 		}
 		return null;
 	}
 
 	private static boolean isRename(DiffEntry ent) {
 		return ent.getChangeType() == ChangeType.RENAME
 				|| ent.getChangeType() == ChangeType.COPY;
 	}
 }