/*
    * Copyright (C) 2009-2010, 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
    *
   * 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,
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   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
   * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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  package org.eclipse.jgit.junit;
  
  import static java.nio.charset.StandardCharsets.UTF_8;
  import static org.junit.Assert.assertEquals;
  import static org.junit.Assert.fail;
  
  import java.io.BufferedOutputStream;
  import java.io.File;
  import java.io.FileOutputStream;
  import java.io.IOException;
  import java.io.OutputStream;
  import java.security.MessageDigest;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Collections;
  import java.util.Date;
  import java.util.HashSet;
  import java.util.List;
  import java.util.Set;
  import java.util.TimeZone;
  
  import org.eclipse.jgit.api.Git;
  import org.eclipse.jgit.dircache.DirCache;
  import org.eclipse.jgit.dircache.DirCacheBuilder;
  import org.eclipse.jgit.dircache.DirCacheEditor;
  import org.eclipse.jgit.dircache.DirCacheEditor.DeletePath;
  import org.eclipse.jgit.dircache.DirCacheEditor.DeleteTree;
  import org.eclipse.jgit.dircache.DirCacheEditor.PathEdit;
  import org.eclipse.jgit.dircache.DirCacheEntry;
  import org.eclipse.jgit.errors.IncorrectObjectTypeException;
  import org.eclipse.jgit.errors.MissingObjectException;
  import org.eclipse.jgit.errors.ObjectWritingException;
  import org.eclipse.jgit.internal.storage.file.FileRepository;
  import org.eclipse.jgit.internal.storage.file.LockFile;
  import org.eclipse.jgit.internal.storage.file.ObjectDirectory;
  import org.eclipse.jgit.internal.storage.file.PackFile;
  import org.eclipse.jgit.internal.storage.file.PackIndex.MutableEntry;
  import org.eclipse.jgit.internal.storage.pack.PackWriter;
  import org.eclipse.jgit.lib.AnyObjectId;
  import org.eclipse.jgit.lib.Constants;
  import org.eclipse.jgit.lib.FileMode;
  import org.eclipse.jgit.lib.NullProgressMonitor;
  import org.eclipse.jgit.lib.ObjectChecker;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.ObjectInserter;
  import org.eclipse.jgit.lib.PersonIdent;
  import org.eclipse.jgit.lib.Ref;
  import org.eclipse.jgit.lib.RefUpdate;
  import org.eclipse.jgit.lib.RefWriter;
  import org.eclipse.jgit.lib.Repository;
  import org.eclipse.jgit.lib.TagBuilder;
  import org.eclipse.jgit.merge.MergeStrategy;
  import org.eclipse.jgit.merge.ThreeWayMerger;
  import org.eclipse.jgit.revwalk.ObjectWalk;
  import org.eclipse.jgit.revwalk.RevBlob;
  import org.eclipse.jgit.revwalk.RevCommit;
 import org.eclipse.jgit.revwalk.RevObject;
 import org.eclipse.jgit.revwalk.RevTag;
 import org.eclipse.jgit.revwalk.RevTree;
 import org.eclipse.jgit.revwalk.RevWalk;
 import org.eclipse.jgit.treewalk.TreeWalk;
 import org.eclipse.jgit.treewalk.filter.PathFilterGroup;
 import org.eclipse.jgit.util.ChangeIdUtil;
 import org.eclipse.jgit.util.FileUtils;
 
 /**
  * Wrapper to make creating test data easier.
  *
  * @param <R>
  *            type of Repository the test data is stored on.
  */
 public class TestRepository<R extends Repository> {
 
 	/** Constant <code>AUTHOR="J. Author"</code> */
 	public static final String AUTHOR = "J. Author";
 
 	/** Constant <code>AUTHOR_EMAIL="jauthor@example.com"</code> */
 	public static final String AUTHOR_EMAIL = "jauthor@example.com";
 
 	/** Constant <code>COMMITTER="J. Committer"</code> */
 	public static final String COMMITTER = "J. Committer";
 
 	/** Constant <code>COMMITTER_EMAIL="jcommitter@example.com"</code> */
 	public static final String COMMITTER_EMAIL = "jcommitter@example.com";
 
 	private final PersonIdent defaultAuthor;
 
 	private final PersonIdent defaultCommitter;
 
 	private final R db;
 
 	private final Git git;
 
 	private final RevWalk pool;
 
 	private final ObjectInserter inserter;
 
 	private final MockSystemReader mockSystemReader;
 
 	/**
 	 * Wrap a repository with test building tools.
 	 *
 	 * @param db
 	 *            the test repository to write into.
 	 * @throws IOException
 	 */
 	public TestRepository(R db) throws IOException {
 		this(db, new RevWalk(db), new MockSystemReader());
 	}
 
 	/**
 	 * Wrap a repository with test building tools.
 	 *
 	 * @param db
 	 *            the test repository to write into.
 	 * @param rw
 	 *            the RevObject pool to use for object lookup.
 	 * @throws IOException
 	 */
 	public TestRepository(R db, RevWalk rw) throws IOException {
 		this(db, rw, new MockSystemReader());
 	}
 
 	/**
 	 * Wrap a repository with test building tools.
 	 *
 	 * @param db
 	 *            the test repository to write into.
 	 * @param rw
 	 *            the RevObject pool to use for object lookup.
 	 * @param reader
 	 *            the MockSystemReader to use for clock and other system
 	 *            operations.
 	 * @throws IOException
 	 * @since 4.2
 	 */
 	public TestRepository(R db, RevWalk rw, MockSystemReader reader)
 			throws IOException {
 		this.db = db;
 		this.git = Git.wrap(db);
 		this.pool = rw;
 		this.inserter = db.newObjectInserter();
 		this.mockSystemReader = reader;
 		long now = mockSystemReader.getCurrentTime();
 		int tz = mockSystemReader.getTimezone(now);
 		defaultAuthor = new PersonIdent(AUTHOR, AUTHOR_EMAIL, now, tz);
 		defaultCommitter = new PersonIdent(COMMITTER, COMMITTER_EMAIL, now, tz);
 	}
 
 	/**
 	 * Get repository
 	 *
 	 * @return the repository this helper class operates against.
 	 */
 	public R getRepository() {
 		return db;
 	}
 
 	/**
 	 * Get RevWalk
 	 *
 	 * @return get the RevWalk pool all objects are allocated through.
 	 */
 	public RevWalk getRevWalk() {
 		return pool;
 	}
 
 	/**
 	 * Return Git API wrapper
 	 *
 	 * @return an API wrapper for the underlying repository. This wrapper does
 	 *         not allocate any new resources and need not be closed (but
 	 *         closing it is harmless).
 	 */
 	public Git git() {
 		return git;
 	}
 
 	/**
 	 * Get date
 	 *
 	 * @return current date.
 	 * @since 4.2
 	 */
 	public Date getDate() {
 		return new Date(mockSystemReader.getCurrentTime());
 	}
 
 	/**
 	 * Get timezone
 	 *
 	 * @return timezone used for default identities.
 	 */
 	public TimeZone getTimeZone() {
 		return mockSystemReader.getTimeZone();
 	}
 
 	/**
 	 * Adjust the current time that will used by the next commit.
 	 *
 	 * @param secDelta
 	 *            number of seconds to add to the current time.
 	 */
 	public void tick(int secDelta) {
 		mockSystemReader.tick(secDelta);
 	}
 
 	/**
 	 * Set the author and committer using {@link #getDate()}.
 	 *
 	 * @param c
 	 *            the commit builder to store.
 	 */
 	public void setAuthorAndCommitter(org.eclipse.jgit.lib.CommitBuilder c) {
 		c.setAuthor(new PersonIdent(defaultAuthor, getDate()));
 		c.setCommitter(new PersonIdent(defaultCommitter, getDate()));
 	}
 
 	/**
 	 * Create a new blob object in the repository.
 	 *
 	 * @param content
 	 *            file content, will be UTF-8 encoded.
 	 * @return reference to the blob.
 	 * @throws Exception
 	 */
 	public RevBlob blob(String content) throws Exception {
 		return blob(content.getBytes(UTF_8));
 	}
 
 	/**
 	 * Create a new blob object in the repository.
 	 *
 	 * @param content
 	 *            binary file content.
 	 * @return the new, fully parsed blob.
 	 * @throws Exception
 	 */
 	public RevBlob blob(byte[] content) throws Exception {
 		ObjectId id;
 		try (ObjectInserter ins = inserter) {
 			id = ins.insert(Constants.OBJ_BLOB, content);
 			ins.flush();
 		}
 		return (RevBlob) pool.parseAny(id);
 	}
 
 	/**
 	 * Construct a regular file mode tree entry.
 	 *
 	 * @param path
 	 *            path of the file.
 	 * @param blob
 	 *            a blob, previously constructed in the repository.
 	 * @return the entry.
 	 * @throws Exception
 	 */
 	public DirCacheEntry file(String path, RevBlob blob)
 			throws Exception {
 		final DirCacheEntry e = new DirCacheEntry(path);
 		e.setFileMode(FileMode.REGULAR_FILE);
 		e.setObjectId(blob);
 		return e;
 	}
 
 	/**
 	 * Construct a tree from a specific listing of file entries.
 	 *
 	 * @param entries
 	 *            the files to include in the tree. The collection does not need
 	 *            to be sorted properly and may be empty.
 	 * @return the new, fully parsed tree specified by the entry list.
 	 * @throws Exception
 	 */
 	public RevTree tree(DirCacheEntry... entries) throws Exception {
 		final DirCache dc = DirCache.newInCore();
 		final DirCacheBuilder b = dc.builder();
 		for (DirCacheEntry e : entries) {
 			b.add(e);
 		}
 		b.finish();
 		ObjectId root;
 		try (ObjectInserter ins = inserter) {
 			root = dc.writeTree(ins);
 			ins.flush();
 		}
 		return pool.parseTree(root);
 	}
 
 	/**
 	 * Lookup an entry stored in a tree, failing if not present.
 	 *
 	 * @param tree
 	 *            the tree to search.
 	 * @param path
 	 *            the path to find the entry of.
 	 * @return the parsed object entry at this path, never null.
 	 * @throws Exception
 	 */
 	public RevObject get(RevTree tree, String path)
 			throws Exception {
 		try (TreeWalk tw = new TreeWalk(pool.getObjectReader())) {
 			tw.setFilter(PathFilterGroup.createFromStrings(Collections
 					.singleton(path)));
 			tw.reset(tree);
 			while (tw.next()) {
 				if (tw.isSubtree() && !path.equals(tw.getPathString())) {
 					tw.enterSubtree();
 					continue;
 				}
 				final ObjectId entid = tw.getObjectId(0);
 				final FileMode entmode = tw.getFileMode(0);
 				return pool.lookupAny(entid, entmode.getObjectType());
 			}
 		}
 		fail("Can't find " + path + " in tree " + tree.name());
 		return null; // never reached.
 	}
 
 	/**
 	 * Create a new commit.
 	 * <p>
 	 * See {@link #commit(int, RevTree, RevCommit...)}. The tree is the empty
 	 * tree (no files or subdirectories).
 	 *
 	 * @param parents
 	 *            zero or more parents of the commit.
 	 * @return the new commit.
 	 * @throws Exception
 	 */
 	public RevCommit commit(RevCommit... parents) throws Exception {
 		return commit(1, tree(), parents);
 	}
 
 	/**
 	 * Create a new commit.
 	 * <p>
 	 * See {@link #commit(int, RevTree, RevCommit...)}.
 	 *
 	 * @param tree
 	 *            the root tree for the commit.
 	 * @param parents
 	 *            zero or more parents of the commit.
 	 * @return the new commit.
 	 * @throws Exception
 	 */
 	public RevCommit commit(RevTree tree, RevCommit... parents)
 			throws Exception {
 		return commit(1, tree, parents);
 	}
 
 	/**
 	 * Create a new commit.
 	 * <p>
 	 * See {@link #commit(int, RevTree, RevCommit...)}. The tree is the empty
 	 * tree (no files or subdirectories).
 	 *
 	 * @param secDelta
 	 *            number of seconds to advance {@link #tick(int)} by.
 	 * @param parents
 	 *            zero or more parents of the commit.
 	 * @return the new commit.
 	 * @throws Exception
 	 */
 	public RevCommit commit(int secDelta, RevCommit... parents)
 			throws Exception {
 		return commit(secDelta, tree(), parents);
 	}
 
 	/**
 	 * Create a new commit.
 	 * <p>
 	 * The author and committer identities are stored using the current
 	 * timestamp, after being incremented by {@code secDelta}. The message body
 	 * is empty.
 	 *
 	 * @param secDelta
 	 *            number of seconds to advance {@link #tick(int)} by.
 	 * @param tree
 	 *            the root tree for the commit.
 	 * @param parents
 	 *            zero or more parents of the commit.
 	 * @return the new, fully parsed commit.
 	 * @throws Exception
 	 */
 	public RevCommit commit(final int secDelta, final RevTree tree,
 			final RevCommit... parents) throws Exception {
 		tick(secDelta);
 
 		final org.eclipse.jgit.lib.CommitBuilder c;
 
 		c = new org.eclipse.jgit.lib.CommitBuilder();
 		c.setTreeId(tree);
 		c.setParentIds(parents);
 		c.setAuthor(new PersonIdent(defaultAuthor, getDate()));
 		c.setCommitter(new PersonIdent(defaultCommitter, getDate()));
 		c.setMessage("");
 		ObjectId id;
 		try (ObjectInserter ins = inserter) {
 			id = ins.insert(c);
 			ins.flush();
 		}
 		return pool.parseCommit(id);
 	}
 
 	/**
 	 * Create commit builder
 	 *
 	 * @return a new commit builder.
 	 */
 	public CommitBuilder commit() {
 		return new CommitBuilder();
 	}
 
 	/**
 	 * Construct an annotated tag object pointing at another object.
 	 * <p>
 	 * The tagger is the committer identity, at the current time as specified by
 	 * {@link #tick(int)}. The time is not increased.
 	 * <p>
 	 * The tag message is empty.
 	 *
 	 * @param name
 	 *            name of the tag. Traditionally a tag name should not start
 	 *            with {@code refs/tags/}.
 	 * @param dst
 	 *            object the tag should be pointed at.
 	 * @return the new, fully parsed annotated tag object.
 	 * @throws Exception
 	 */
 	public RevTag tag(String name, RevObject dst) throws Exception {
 		final TagBuilder t = new TagBuilder();
 		t.setObjectId(dst);
 		t.setTag(name);
 		t.setTagger(new PersonIdent(defaultCommitter, getDate()));
 		t.setMessage("");
 		ObjectId id;
 		try (ObjectInserter ins = inserter) {
 			id = ins.insert(t);
 			ins.flush();
 		}
 		return pool.parseTag(id);
 	}
 
 	/**
 	 * Update a reference to point to an object.
 	 *
 	 * @param ref
 	 *            the name of the reference to update to. If {@code ref} does
 	 *            not start with {@code refs/} and is not the magic names
 	 *            {@code HEAD} {@code FETCH_HEAD} or {@code MERGE_HEAD}, then
 	 *            {@code refs/heads/} will be prefixed in front of the given
 	 *            name, thereby assuming it is a branch.
 	 * @param to
 	 *            the target object.
 	 * @return the target object.
 	 * @throws Exception
 	 */
 	public RevCommit update(String ref, CommitBuilder to) throws Exception {
 		return update(ref, to.create());
 	}
 
 	/**
 	 * Amend an existing ref.
 	 *
 	 * @param ref
 	 *            the name of the reference to amend, which must already exist.
 	 *            If {@code ref} does not start with {@code refs/} and is not the
 	 *            magic names {@code HEAD} {@code FETCH_HEAD} or {@code
 	 *            MERGE_HEAD}, then {@code refs/heads/} will be prefixed in front
 	 *            of the given name, thereby assuming it is a branch.
 	 * @return commit builder that amends the branch on commit.
 	 * @throws Exception
 	 */
 	public CommitBuilder amendRef(String ref) throws Exception {
 		String name = normalizeRef(ref);
 		Ref r = db.exactRef(name);
 		if (r == null)
 			throw new IOException("Not a ref: " + ref);
 		return amend(pool.parseCommit(r.getObjectId()), branch(name).commit());
 	}
 
 	/**
 	 * Amend an existing commit.
 	 *
 	 * @param id
 	 *            the id of the commit to amend.
 	 * @return commit builder.
 	 * @throws Exception
 	 */
 	public CommitBuilder amend(AnyObjectId id) throws Exception {
 		return amend(pool.parseCommit(id), commit());
 	}
 
 	private CommitBuilder amend(RevCommit old, CommitBuilder b) throws Exception {
 		pool.parseBody(old);
 		b.author(old.getAuthorIdent());
 		b.committer(old.getCommitterIdent());
 		b.message(old.getFullMessage());
 		// Use the committer name from the old commit, but update it after ticking
 		// the clock in CommitBuilder#create().
 		b.updateCommitterTime = true;
 
 		// Reset parents to original parents.
 		b.noParents();
 		for (int i = 0; i < old.getParentCount(); i++)
 			b.parent(old.getParent(i));
 
 		// Reset tree to original tree; resetting parents reset tree contents to the
 		// first parent.
 		b.tree.clear();
 		try (TreeWalk tw = new TreeWalk(db)) {
 			tw.reset(old.getTree());
 			tw.setRecursive(true);
 			while (tw.next()) {
 				b.edit(new PathEdit(tw.getPathString()) {
 					@Override
 					public void apply(DirCacheEntry ent) {
 						ent.setFileMode(tw.getFileMode(0));
 						ent.setObjectId(tw.getObjectId(0));
 					}
 				});
 			}
 		}
 
 		return b;
 	}
 
 	/**
 	 * Update a reference to point to an object.
 	 *
 	 * @param <T>
 	 *            type of the target object.
 	 * @param ref
 	 *            the name of the reference to update to. If {@code ref} does
 	 *            not start with {@code refs/} and is not the magic names
 	 *            {@code HEAD} {@code FETCH_HEAD} or {@code MERGE_HEAD}, then
 	 *            {@code refs/heads/} will be prefixed in front of the given
 	 *            name, thereby assuming it is a branch.
 	 * @param obj
 	 *            the target object.
 	 * @return the target object.
 	 * @throws Exception
 	 */
 	public <T extends AnyObjectId> T update(String ref, T obj) throws Exception {
 		ref = normalizeRef(ref);
 		RefUpdate u = db.updateRef(ref);
 		u.setNewObjectId(obj);
 		switch (u.forceUpdate()) {
 		case FAST_FORWARD:
 		case FORCED:
 		case NEW:
 		case NO_CHANGE:
 			updateServerInfo();
 			return obj;
 
 		default:
 			throw new IOException("Cannot write " + ref + " " + u.getResult());
 		}
 	}
 
 	/**
 	 * Delete a reference.
 	 *
 	 * @param ref
 	 *	      the name of the reference to delete. This is normalized
 	 *	      in the same way as {@link #update(String, AnyObjectId)}.
 	 * @throws Exception
 	 * @since 4.4
 	 */
 	public void delete(String ref) throws Exception {
 		ref = normalizeRef(ref);
 		RefUpdate u = db.updateRef(ref);
 		u.setForceUpdate(true);
 		switch (u.delete()) {
 		case FAST_FORWARD:
 		case FORCED:
 		case NEW:
 		case NO_CHANGE:
 			updateServerInfo();
 			return;
 
 		default:
 			throw new IOException("Cannot delete " + ref + " " + u.getResult());
 		}
 	}
 
 	private static String normalizeRef(String ref) {
 		if (Constants.HEAD.equals(ref)) {
 			// nothing
 		} else if ("FETCH_HEAD".equals(ref)) {
 			// nothing
 		} else if ("MERGE_HEAD".equals(ref)) {
 			// nothing
 		} else if (ref.startsWith(Constants.R_REFS)) {
 			// nothing
 		} else
 			ref = Constants.R_HEADS + ref;
 		return ref;
 	}
 
 	/**
 	 * Soft-reset HEAD to a detached state.
 	 *
 	 * @param id
 	 *            ID of detached head.
 	 * @throws Exception
 	 * @see #reset(String)
 	 */
 	public void reset(AnyObjectId id) throws Exception {
 		RefUpdate ru = db.updateRef(Constants.HEAD, true);
 		ru.setNewObjectId(id);
 		RefUpdate.Result result = ru.forceUpdate();
 		switch (result) {
 			case FAST_FORWARD:
 			case FORCED:
 			case NEW:
 			case NO_CHANGE:
 				break;
 			default:
 				throw new IOException(String.format(
 						"Checkout \"%s\" failed: %s", id.name(), result));
 		}
 	}
 
 	/**
 	 * Soft-reset HEAD to a different commit.
 	 * <p>
 	 * This is equivalent to {@code git reset --soft} in that it modifies HEAD but
 	 * not the index or the working tree of a non-bare repository.
 	 *
 	 * @param name
 	 *            revision string; either an existing ref name, or something that
 	 *            can be parsed to an object ID.
 	 * @throws Exception
 	 */
 	public void reset(String name) throws Exception {
 		RefUpdate.Result result;
 		ObjectId id = db.resolve(name);
 		if (id == null)
 			throw new IOException("Not a revision: " + name);
 		RefUpdate ru = db.updateRef(Constants.HEAD, false);
 		ru.setNewObjectId(id);
 		result = ru.forceUpdate();
 		switch (result) {
 			case FAST_FORWARD:
 			case FORCED:
 			case NEW:
 			case NO_CHANGE:
 				break;
 			default:
 				throw new IOException(String.format(
 						"Checkout \"%s\" failed: %s", name, result));
 		}
 	}
 
 	/**
 	 * Cherry-pick a commit onto HEAD.
 	 * <p>
 	 * This differs from {@code git cherry-pick} in that it works in a bare
 	 * repository. As a result, any merge failure results in an exception, as
 	 * there is no way to recover.
 	 *
 	 * @param id
 	 *            commit-ish to cherry-pick.
 	 * @return the new, fully parsed commit, or null if no work was done due to
 	 *         the resulting tree being identical.
 	 * @throws Exception
 	 */
 	public RevCommit cherryPick(AnyObjectId id) throws Exception {
 		RevCommit commit = pool.parseCommit(id);
 		pool.parseBody(commit);
 		if (commit.getParentCount() != 1)
 			throw new IOException(String.format(
 					"Expected 1 parent for %s, found: %s",
 					id.name(), Arrays.asList(commit.getParents())));
 		RevCommit parent = commit.getParent(0);
 		pool.parseHeaders(parent);
 
 		Ref headRef = db.exactRef(Constants.HEAD);
 		if (headRef == null)
 			throw new IOException("Missing HEAD");
 		RevCommit head = pool.parseCommit(headRef.getObjectId());
 
 		ThreeWayMerger merger = MergeStrategy.RECURSIVE.newMerger(db, true);
 		merger.setBase(parent.getTree());
 		if (merger.merge(head, commit)) {
 			if (AnyObjectId.equals(head.getTree(), merger.getResultTreeId()))
 				return null;
 			tick(1);
 			org.eclipse.jgit.lib.CommitBuilder b =
 					new org.eclipse.jgit.lib.CommitBuilder();
 			b.setParentId(head);
 			b.setTreeId(merger.getResultTreeId());
 			b.setAuthor(commit.getAuthorIdent());
 			b.setCommitter(new PersonIdent(defaultCommitter, getDate()));
 			b.setMessage(commit.getFullMessage());
 			ObjectId result;
 			try (ObjectInserter ins = inserter) {
 				result = ins.insert(b);
 				ins.flush();
 			}
 			update(Constants.HEAD, result);
 			return pool.parseCommit(result);
 		} else {
 			throw new IOException("Merge conflict");
 		}
 	}
 
 	/**
 	 * Update the dumb client server info files.
 	 *
 	 * @throws Exception
 	 */
 	public void updateServerInfo() throws Exception {
 		if (db instanceof FileRepository) {
 			final FileRepository fr = (FileRepository) db;
 			RefWriter rw = new RefWriter(fr.getRefDatabase().getRefs()) {
 				@Override
 				protected void writeFile(String name, byte[] bin)
 						throws IOException {
 					File path = new File(fr.getDirectory(), name);
 					TestRepository.this.writeFile(path, bin);
 				}
 			};
 			rw.writePackedRefs();
 			rw.writeInfoRefs();
 
 			final StringBuilder w = new StringBuilder();
 			for (PackFile p : fr.getObjectDatabase().getPacks()) {
 				w.append("P ");
 				w.append(p.getPackFile().getName());
 				w.append('\n');
 			}
 			writeFile(new File(new File(fr.getObjectDatabase().getDirectory(),
 					"info"), "packs"), Constants.encodeASCII(w.toString()));
 		}
 	}
 
 	/**
 	 * Ensure the body of the given object has been parsed.
 	 *
 	 * @param <T>
 	 *            type of object, e.g. {@link org.eclipse.jgit.revwalk.RevTag}
 	 *            or {@link org.eclipse.jgit.revwalk.RevCommit}.
 	 * @param object
 	 *            reference to the (possibly unparsed) object to force body
 	 *            parsing of.
 	 * @return {@code object}
 	 * @throws Exception
 	 */
 	public <T extends RevObject> T parseBody(T object) throws Exception {
 		pool.parseBody(object);
 		return object;
 	}
 
 	/**
 	 * Create a new branch builder for this repository.
 	 *
 	 * @param ref
 	 *            name of the branch to be constructed. If {@code ref} does not
 	 *            start with {@code refs/} the prefix {@code refs/heads/} will
 	 *            be added.
 	 * @return builder for the named branch.
 	 */
 	public BranchBuilder branch(String ref) {
 		if (Constants.HEAD.equals(ref)) {
 			// nothing
 		} else if (ref.startsWith(Constants.R_REFS)) {
 			// nothing
 		} else
 			ref = Constants.R_HEADS + ref;
 		return new BranchBuilder(ref);
 	}
 
 	/**
 	 * Tag an object using a lightweight tag.
 	 *
 	 * @param name
 	 *            the tag name. The /refs/tags/ prefix will be added if the name
 	 *            doesn't start with it
 	 * @param obj
 	 *            the object to tag
 	 * @return the tagged object
 	 * @throws Exception
 	 */
 	public ObjectId lightweightTag(String name, ObjectId obj) throws Exception {
 		if (!name.startsWith(Constants.R_TAGS))
 			name = Constants.R_TAGS + name;
 		return update(name, obj);
 	}
 
 	/**
 	 * Run consistency checks against the object database.
 	 * <p>
 	 * This method completes silently if the checks pass. A temporary revision
 	 * pool is constructed during the checking.
 	 *
 	 * @param tips
 	 *            the tips to start checking from; if not supplied the refs of
 	 *            the repository are used instead.
 	 * @throws MissingObjectException
 	 * @throws IncorrectObjectTypeException
 	 * @throws IOException
 	 */
 	public void fsck(RevObject... tips) throws MissingObjectException,
 			IncorrectObjectTypeException, IOException {
 		try (ObjectWalk ow = new ObjectWalk(db)) {
 			if (tips.length != 0) {
 				for (RevObject o : tips)
 					ow.markStart(ow.parseAny(o));
 			} else {
 				for (Ref r : db.getRefDatabase().getRefs())
 					ow.markStart(ow.parseAny(r.getObjectId()));
 			}
 
 			ObjectChecker oc = new ObjectChecker();
 			for (;;) {
 				final RevCommit o = ow.next();
 				if (o == null)
 					break;
 
 				final byte[] bin = db.open(o, o.getType()).getCachedBytes();
 				oc.checkCommit(o, bin);
 				assertHash(o, bin);
 			}
 
 			for (;;) {
 				final RevObject o = ow.nextObject();
 				if (o == null)
 					break;
 
 				final byte[] bin = db.open(o, o.getType()).getCachedBytes();
 				oc.check(o, o.getType(), bin);
 				assertHash(o, bin);
 			}
 		}
 	}
 
 	private static void assertHash(RevObject id, byte[] bin) {
 		MessageDigest md = Constants.newMessageDigest();
 		md.update(Constants.encodedTypeString(id.getType()));
 		md.update((byte) ' ');
 		md.update(Constants.encodeASCII(bin.length));
 		md.update((byte) 0);
 		md.update(bin);
 		assertEquals(id, ObjectId.fromRaw(md.digest()));
 	}
 
 	/**
 	 * Pack all reachable objects in the repository into a single pack file.
 	 * <p>
 	 * All loose objects are automatically pruned. Existing packs however are
 	 * not removed.
 	 *
 	 * @throws Exception
 	 */
 	public void packAndPrune() throws Exception {
 		if (db.getObjectDatabase() instanceof ObjectDirectory) {
 			ObjectDirectory odb = (ObjectDirectory) db.getObjectDatabase();
 			NullProgressMonitor m = NullProgressMonitor.INSTANCE;
 
 			final File pack, idx;
 			try (PackWriter pw = new PackWriter(db)) {
 				Set<ObjectId> all = new HashSet<>();
 				for (Ref r : db.getRefDatabase().getRefs())
 					all.add(r.getObjectId());
 				pw.preparePack(m, all, PackWriter.NONE);
 
 				final ObjectId name = pw.computeName();
 
 				pack = nameFor(odb, name, ".pack");
 				try (OutputStream out =
 						new BufferedOutputStream(new FileOutputStream(pack))) {
 					pw.writePack(m, m, out);
 				}
 				pack.setReadOnly();
 
 				idx = nameFor(odb, name, ".idx");
 				try (OutputStream out =
 						new BufferedOutputStream(new FileOutputStream(idx))) {
 					pw.writeIndex(out);
 				}
 				idx.setReadOnly();
 			}
 
 			odb.openPack(pack);
 			updateServerInfo();
 			prunePacked(odb);
 		}
 	}
 
 	private static void prunePacked(ObjectDirectory odb) throws IOException {
 		for (PackFile p : odb.getPacks()) {
 			for (MutableEntry e : p)
 				FileUtils.delete(odb.fileFor(e.toObjectId()));
 		}
 	}
 
 	private static File nameFor(ObjectDirectory odb, ObjectId name, String t) {
 		File packdir = odb.getPackDirectory();
 		return new File(packdir, "pack-" + name.name() + t);
 	}
 
 	private void writeFile(File p, byte[] bin) throws IOException,
 			ObjectWritingException {
 		final LockFile lck = new LockFile(p);
 		if (!lck.lock())
 			throw new ObjectWritingException("Can't write " + p);
 		try {
 			lck.write(bin);
 		} catch (IOException ioe) {
 			throw new ObjectWritingException("Can't write " + p);
 		}
 		if (!lck.commit())
 			throw new ObjectWritingException("Can't write " + p);
 	}
 
 	/** Helper to build a branch with one or more commits */
 	public class BranchBuilder {
 		private final String ref;
 
 		BranchBuilder(String ref) {
 			this.ref = ref;
 		}
 
 		/**
 		 * @return construct a new commit builder that updates this branch. If
 		 *         the branch already exists, the commit builder will have its
 		 *         first parent as the current commit and its tree will be
 		 *         initialized to the current files.
 		 * @throws Exception
 		 *             the commit builder can't read the current branch state
 		 */
 		public CommitBuilder commit() throws Exception {
 			return new CommitBuilder(this);
 		}
 
 		/**
 		 * Forcefully update this branch to a particular commit.
 		 *
 		 * @param to
 		 *            the commit to update to.
 		 * @return {@code to}.
 		 * @throws Exception
 		 */
 		public RevCommit update(CommitBuilder to) throws Exception {
 			return update(to.create());
 		}
 
 		/**
 		 * Forcefully update this branch to a particular commit.
 		 *
 		 * @param to
 		 *            the commit to update to.
 		 * @return {@code to}.
 		 * @throws Exception
 		 */
 		public RevCommit update(RevCommit to) throws Exception {
 			return TestRepository.this.update(ref, to);
 		}
 
 		/**
 		 * Delete this branch.
 		 * @throws Exception
 		 * @since 4.4
 		 */
 		public void delete() throws Exception {
 			TestRepository.this.delete(ref);
 		}
 	}
 
 	/** Helper to generate a commit. */
 	public class CommitBuilder {
 		private final BranchBuilder branch;
 
 		private final DirCache tree = DirCache.newInCore();
 
 		private ObjectId topLevelTree;
 
 		private final List<RevCommit> parents = new ArrayList<>(2);
 
 		private int tick = 1;
 
 		private String message = "";
 
 		private RevCommit self;
 
 		private PersonIdent author;
 		private PersonIdent committer;
 
 		private String changeId;
 
 		private boolean updateCommitterTime;
 
 		CommitBuilder() {
 			branch = null;
 		}
 
 		CommitBuilder(BranchBuilder b) throws Exception {
 			branch = b;
 
 			Ref ref = db.exactRef(branch.ref);
 			if (ref != null && ref.getObjectId() != null)
 				parent(pool.parseCommit(ref.getObjectId()));
 		}
 
 		CommitBuilder(CommitBuilder prior) throws Exception {
 			branch = prior.branch;
 
 			DirCacheBuilder b = tree.builder();
 			for (int i = 0; i < prior.tree.getEntryCount(); i++)
 				b.add(prior.tree.getEntry(i));
 			b.finish();
 
 			parents.add(prior.create());
 		}
 
 		public CommitBuilder parent(RevCommit p) throws Exception {
 			if (parents.isEmpty()) {
 				DirCacheBuilder b = tree.builder();
 				parseBody(p);
 				b.addTree(new byte[0], DirCacheEntry.STAGE_0, pool
 						.getObjectReader(), p.getTree());
 				b.finish();
 			}
 			parents.add(p);
 			return this;
 		}
 
 		public List<RevCommit> parents() {
 			return Collections.unmodifiableList(parents);
 		}
 
 		public CommitBuilder noParents() {
 			parents.clear();
 			return this;
 		}
 
 		public CommitBuilder noFiles() {
 			tree.clear();
 			return this;
 		}
 
 		public CommitBuilder setTopLevelTree(ObjectId treeId) {
 			topLevelTree = treeId;
 			return this;
 		}
 
 		public CommitBuilder add(String path, String content) throws Exception {
 			return add(path, blob(content));
 		}
 
 		public CommitBuilder add(String path, RevBlob id)
 				throws Exception {
 			return edit(new PathEdit(path) {
 				@Override
 				public void apply(DirCacheEntry ent) {
 					ent.setFileMode(FileMode.REGULAR_FILE);
 					ent.setObjectId(id);
 				}
 			});
 		}
 
 		public CommitBuilder edit(PathEdit edit) {
 			DirCacheEditor e = tree.editor();
 			e.add(edit);
 			e.finish();
 			return this;
 		}
 
 		public CommitBuilder rm(String path) {
 			DirCacheEditor e = tree.editor();
 			e.add(new DeletePath(path));
 			e.add(new DeleteTree(path));
 			e.finish();
 			return this;
 		}
 
 		public CommitBuilder message(String m) {
 			message = m;
 			return this;
 		}
 
 		public String message() {
 			return message;
 		}
 
 		public CommitBuilder tick(int secs) {
 			tick = secs;
 			return this;
 		}
 
 		public CommitBuilder ident(PersonIdent ident) {
 			author = ident;
 			committer = ident;
 			return this;
 		}
 
 		public CommitBuilder author(PersonIdent a) {
 			author = a;
 			return this;
 		}
 
 		public PersonIdent author() {
 			return author;
 		}
 
 		public CommitBuilder committer(PersonIdent c) {
 			committer = c;
 			return this;
 		}
 
 		public PersonIdent committer() {
 			return committer;
 		}
 
 		public CommitBuilder insertChangeId() {
 			changeId = "";
 			return this;
 		}
 
 		public CommitBuilder insertChangeId(String c) {
 			// Validate, but store as a string so we can use "" as a sentinel.
 			ObjectId.fromString(c);
 			changeId = c;
 			return this;
 		}
 
 		public RevCommit create() throws Exception {
 			if (self == null) {
 				TestRepository.this.tick(tick);
 
 				final org.eclipse.jgit.lib.CommitBuilder c;
 
 				c = new org.eclipse.jgit.lib.CommitBuilder();
 				c.setParentIds(parents);
 				setAuthorAndCommitter(c);
 				if (author != null)
 					c.setAuthor(author);
 				if (committer != null) {
 					if (updateCommitterTime)
 						committer = new PersonIdent(committer, getDate());
 					c.setCommitter(committer);
 				}
 
 				ObjectId commitId;
 				try (ObjectInserter ins = inserter) {
 					if (topLevelTree != null)
 						c.setTreeId(topLevelTree);
 					else
 						c.setTreeId(tree.writeTree(ins));
 					insertChangeId(c);
 					c.setMessage(message);
 					commitId = ins.insert(c);
 					ins.flush();
 				}
 				self = pool.parseCommit(commitId);
 
 				if (branch != null)
 					branch.update(self);
 			}
 			return self;
 		}
 
 		private void insertChangeId(org.eclipse.jgit.lib.CommitBuilder c) {
 			if (changeId == null)
 				return;
 			int idx = ChangeIdUtil.indexOfChangeId(message, "\n");
 			if (idx >= 0)
 				return;
 
 			ObjectId firstParentId = null;
 			if (!parents.isEmpty())
 				firstParentId = parents.get(0);
 
 			ObjectId cid;
 			if (changeId.equals(""))
 				cid = ChangeIdUtil.computeChangeId(c.getTreeId(), firstParentId,
 						c.getAuthor(), c.getCommitter(), message);
 			else
 				cid = ObjectId.fromString(changeId);
 			message = ChangeIdUtil.insertId(message, cid);
 			if (cid != null)
 				message = message.replaceAll("\nChange-Id: I" //$NON-NLS-1$
 						+ ObjectId.zeroId().getName() + "\n", "\nChange-Id: I" //$NON-NLS-1$ //$NON-NLS-2$
 						+ cid.getName() + "\n"); //$NON-NLS-1$
 		}
 
 		public CommitBuilder child() throws Exception {
 			return new CommitBuilder(this);
 		}
 	}
 }