/*
 * 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
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

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.annotations.Nullable;
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.
 Applications that want a simple one-shot computation of blame for a file should use 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. 
 Applications that want more incremental update behavior may use either the raw next() streaming approach supported by this class, or construct a BlameResult using BlameResult.create(BlameGenerator) and incrementally construct the result with BlameResult.computeNext(). 

This class is not thread-safe.

An instance of BlameGenerator can only be used once. To blame multiple files
the application must create a new BlameGenerator.

During blame processing there are two files involved:

result - The file whose lines are being examined. This is the revision
the user is trying to view blame/annotation information alongside of.
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.


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.
/**
 * 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 org.eclipse.jgit.blame.BlameResult} using
 * {@link org.eclipse.jgit.blame.BlameResult#create(BlameGenerator)} and
 * incrementally construct the result with
 * {@link org.eclipse.jgit.blame.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. /** Revision pool used to acquire commits from. */
	private RevWalk revPool;

	
Indicates the commit was put into the queue at least once. /** 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. /** Potential candidates, sorted by commit time descending. */
	private Candidate queue;

	
Number of lines that still need to be discovered. /** Number of lines that still need to be discovered. */
	private int remaining;

	
Blame is currently assigned to this source. /** 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)
Params:
repository – 
           repository to access revision data from.
path – 
           initial path of the file to start scanning (relative to the
           repository)./**
	 * 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);
	}

	
Get repository
Returns:
repository being scanned for revision history/**
	 * Get repository
	 *
	 * @return repository being scanned for revision history
	 */
	public Repository getRepository() {
		return repository;
	}

	
Get result path
Returns:
path file path being processed/**
	 * Get result path
	 *
	 * @return path file path being processed
	 */
	public String getResultPath() {
		return resultPath.getPath();
	}

	
Difference algorithm to use when comparing revisions.
Params:
algorithm –  a DiffAlgorithm
Returns:
this/**
	 * Difference algorithm to use when comparing revisions.
	 *
	 * @param algorithm
	 *            a {@link org.eclipse.jgit.diff.DiffAlgorithm}
	 * @return {@code this}
	 */
	public BlameGenerator setDiffAlgorithm(DiffAlgorithm algorithm) {
		diffAlgorithm = algorithm;
		return this;
	}

	
Text comparator to use when comparing revisions.
Params:
comparator –  a RawTextComparator
Returns:
this/**
	 * Text comparator to use when comparing revisions.
	 *
	 * @param comparator
	 *            a {@link org.eclipse.jgit.diff.RawTextComparator}
	 * @return {@code this}
	 */
	public BlameGenerator setTextComparator(RawTextComparator comparator) {
		textComparator = comparator;
		return this;
	}

	
Enable (or disable) following file renames, on by default.
 If true renames are followed using the standard FollowFilter behavior used by RevWalk (which matches git log --follow in the C implementation). This is not the same as copy/move detection as implemented by the C implementation's of git blame -M -C. 
Params:
follow – 
           enable following.
Returns:
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, allowing the application to configure its
settings for rename score and breaking behavior.
Returns:
the rename detector, or null if setFollowFileRenames(false)./**
	 * Obtain the RenameDetector, allowing the application to configure its
	 * settings for rename score and breaking behavior.
	 *
	 * @return the rename detector, or {@code null} if
	 *         {@code setFollowFileRenames(false)}.
	 */
	@Nullable
	public RenameDetector getRenameDetector() {
		return renameDetector;
	}

	
Push a candidate blob onto the generator's traversal stack.

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).
Params:
description – 
           description of the blob revision, such as "Working Tree".
contents – 
           contents of the file.
Throws:
IOException – 
            the repository cannot be read.
Returns:
this/**
	 * 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 java.io.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.

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).
Params:
description – 
           description of the blob revision, such as "Working Tree".
contents – 
           contents of the file.
Throws:
IOException – 
            the repository cannot be read.
Returns:
this/**
	 * 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 java.io.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(getRepository(), 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.

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).
Params:
description – 
           description of the blob revision, such as "Working Tree".
id – 
           may be a commit or a blob.
Throws:
IOException – 
            the repository cannot be read.
Returns:
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 java.io.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(getRepository(), 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(getRepository(), 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).
 This method is expensive as it immediately runs a RevWalk over the history spanning the expression start..end (end being more recent than start) and then performs the equivalent operation as push(String, AnyObjectId) to begin blame traversal from the commit named by start walking forwards through history until end blaming line deletions. 
 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 BlameResult as it filters these duplicate sources and only remembers the first (oldest) deletion. 
Params:
start – 
           oldest commit to traverse from. The result file will be loaded
           from this commit's tree.
end – 
           most recent commit to stop traversal at. Usually an active
           branch tip, tag, or HEAD.
Throws:
IOException – 
            the repository cannot be read.
Returns:
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 org.eclipse.jgit.blame.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 java.io.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).
 This method is expensive as it immediately runs a RevWalk over the history spanning the expression start..end (end being more recent than start) and then performs the equivalent operation as push(String, AnyObjectId) to begin blame traversal from the commit named by start walking forwards through history until end blaming line deletions. 
 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 BlameResult as it filters these duplicate sources and only remembers the first (oldest) deletion. 
Params:
start – 
           oldest commit to traverse from. The result file will be loaded
           from this commit's tree.
end – 
           most recent commits to stop traversal at. Usually an active
           branch tip, tag, or HEAD.
Throws:
IOException – 
            the repository cannot be read.
Returns:
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 org.eclipse.jgit.blame.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 java.io.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(getRepository(), 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.
Params:
name – 
           unique name of the flag in the blame context.
Returns:
the newly allocated flag.
Since:
3.4/**
	 * 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.
Throws:
IOException – 
            the repository cannot be read.
Returns:
the complete result. Null if no file exists for the given path./**
	 * 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 java.io.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.
Throws:
IOException – 
            repository cannot be read.
Returns:
true if the generator has found a region's source. The getSource* and getResultStart(), getResultEnd() methods can be used to inspect the region found. False if there are no more regions to describe./**
	 * 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 java.io.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 outRegion != null;
	}

	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(getRepository(), 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(getRepository(), 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(getRepository(), 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(getRepository(), 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.

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).
Returns:
current revision being blamed./**
	 * 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;
	}

	
Get source author
Returns:
current author being blamed/**
	 * Get source author
	 *
	 * @return current author being blamed
	 */
	public PersonIdent getSourceAuthor() {
		return outCandidate.getAuthor();
	}

	
Get source committer
Returns:
current committer being blamed/**
	 * Get source committer
	 *
	 * @return current committer being blamed
	 */
	public PersonIdent getSourceCommitter() {
		RevCommit c = getSourceCommit();
		return c != null ? c.getCommitterIdent() : null;
	}

	
Get source path
Returns:
path of the file being blamed/**
	 * Get source path
	 *
	 * @return path of the file being blamed
	 */
	public String getSourcePath() {
		return outCandidate.sourcePath.getPath();
	}

	
Get rename score
Returns:
rename score if a rename occurred in getSourceCommit/**
	 * Get rename score
	 *
	 * @return rename score if a rename occurred in {@link #getSourceCommit}
	 */
	public int getRenameScore() {
		return outCandidate.renameScore;
	}

	
Get first line of the source data that has been blamed for the current
region
Returns:
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 getSourceCommit() in file getSourcePath()./**
	 * Get first line of the source data that has been blamed for the current
	 * region
	 *
	 * @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;
	}

	
Get one past the range of the source data that has been blamed for the
current region
Returns:
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 getSourceCommit() in file getSourcePath()./**
	 * Get one past the range of the source data that has been blamed for the
	 * current region
	 *
	 * @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;
	}

	
Get first line of the result that getSourceCommit() has been blamed for providing 
Returns:
first line of the result that getSourceCommit() has been blamed for providing. Line numbers use 0 based indexing./**
	 * Get first line of the result that {@link #getSourceCommit()} has been
	 * blamed for providing
	 *
	 * @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;
	}

	
Get one past the range of the result that getSourceCommit() has been blamed for providing 
Returns:
one past the range of the result that 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, getResultEnd() is always at least one larger than getResultStart()./**
	 * Get one past the range of the result that {@link #getSourceCommit()} has
	 * been blamed for providing
	 *
	 * @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;
	}

	
Get number of lines in the current region being blamed to getSourceCommit() 
Returns:
number of lines in the current region being blamed to getSourceCommit(). This is always the value of the expression getResultEnd() - getResultStart(), but also getSourceEnd() - getSourceStart()./**
	 * Get number of lines in the current region being blamed to
	 * {@link #getSourceCommit()}
	 *
	 * @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;
	}

	
Get complete contents of the source file blamed for the current output
region
Returns:
complete contents of the source file blamed for the current output region. This is the contents of getSourcePath() within 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./**
	 * Get complete contents of the source file blamed for the current output
	 * region
	 *
	 * @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;
	}

	
Get complete file contents of the result file blame is annotating
Throws:
IOException – 
            repository cannot be read.
IllegalStateException –  next() has already been invoked.
Returns:
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 next(). Returns null if the path does not exist./**
	 * Get complete file contents of the result file blame is annotating
	 *
	 * @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 java.io.IOException
	 *             repository cannot be read.
	 * @throws java.lang.IllegalStateException
	 *             {@link #next()} has already been invoked.
	 */
	public RawText getResultContents() throws IOException {
		return queue != null ? queue.sourceText : null;
	}

	
{@inheritDoc}

Release the current blame session.
Since:
4.0/**
	 * {@inheritDoc}
	 * <p>
	 * 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;
	}
}