Add a NameRevCommand for describing IDs in terms of refnames

The walk logic does not use RevWalk because it needs to walk all paths
to each of the requested commits, keeping track of each path along which
the commit was found in the RevCommit subclass. From these paths, a
single "best" path is chosen based on the total path length, with a
penalty applied for paths that traverse merges.

This functionality parallels "git name-rev".

Change-Id: I92bfb47dd16c898313d2ee525395609c3bf72ebe

2 files changed, 338 insertions, 0 deletions

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/Git.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/Git.java
index 77f951e16f..d36b9bede4 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/api/Git.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/Git.java
@@ -633,6 +633,16 @@ public class Git {
 	}
 
 	/**
+	 * Returns a command object to find human-readable names of revisions.
+	 *
+	 * @return a {@link NameRevCommand}.
+	 * @since 2.3
+	 */
+	public NameRevCommand nameRev() {
+		return new NameRevCommand(repo);
+	}
+
+	/**
 	 * @return the git repository this class is interacting with
 	 */
 	public Repository getRepository() {
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/NameRevCommand.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/NameRevCommand.java
new file mode 100644
index 0000000000..dfae50a725
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/NameRevCommand.java
@@ -0,0 +1,328 @@
+/*
+ * Copyright (C) 2013, 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.api;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+
+import org.eclipse.jgit.api.errors.GitAPIException;
+import org.eclipse.jgit.api.errors.JGitInternalException;
+import org.eclipse.jgit.errors.MissingObjectException;
+import org.eclipse.jgit.lib.AnyObjectId;
+import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.Ref;
+import org.eclipse.jgit.lib.RefDatabase;
+import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.revwalk.FIFORevQueue;
+import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.revwalk.RevObject;
+import org.eclipse.jgit.revwalk.RevTag;
+import org.eclipse.jgit.revwalk.RevWalk;
+
+/**
+ * Command to find human-readable names of revisions.
+ *
+ * @see <a href="http://www.kernel.org/pub/software/scm/git/docs/git-name-rev.html"
+ *      >Git documentation about name-rev</a>
+ */
+public class NameRevCommand extends GitCommand<Map<ObjectId, String>> {
+	/** Amount of slop to allow walking past the earliest requested commit. */
+	private static final int COMMIT_TIME_SLOP = 60 * 60 * 24;
+
+	/** Cost of traversing a merge commit compared to a linear history. */
+	private static final int MERGE_COST = 65535;
+
+	private static class NameRevCommit extends RevCommit {
+		private String tip;
+		private int distance;
+		private long cost;
+
+		private NameRevCommit(AnyObjectId id) {
+			super(id);
+		}
+
+		private StringBuilder format() {
+			StringBuilder sb = new StringBuilder(tip);
+			if (distance > 0)
+				sb.append('~').append(distance);
+			return sb;
+		}
+
+		@Override
+		public String toString() {
+			StringBuilder sb = new StringBuilder(getClass().getSimpleName())
+				.append('[');
+			if (tip != null)
+				sb.append(format());
+			else
+				sb.append(String.valueOf(null));
+			sb.append(',').append(cost).append(']').append(' ')
+				.append(super.toString()).toString();
+			return sb.toString();
+		}
+	}
+
+	private final RevWalk walk;
+	private final List<String> prefixes;
+	private final List<ObjectId> revs;
+
+	/**
+	 * Create a new name-rev command.
+	 *
+	 * @param repo
+	 */
+	protected NameRevCommand(Repository repo) {
+		super(repo);
+		prefixes = new ArrayList<String>(2);
+		revs = new ArrayList<ObjectId>(2);
+		walk = new RevWalk(repo) {
+			@Override
+			public NameRevCommit createCommit(AnyObjectId id) {
+				return new NameRevCommit(id);
+			}
+		};
+	}
+
+	@Override
+	public Map<ObjectId, String> call() throws GitAPIException {
+		try {
+			Map<ObjectId, String> nonCommits = new HashMap<ObjectId, String>();
+			FIFORevQueue pending = new FIFORevQueue();
+			addPrefixes(nonCommits, pending);
+			int cutoff = minCommitTime() - COMMIT_TIME_SLOP;
+
+			while (true) {
+				NameRevCommit c = (NameRevCommit) pending.next();
+				if (c == null)
+					break;
+				if (c.getCommitTime() < cutoff)
+					continue;
+				boolean merge = c.getParentCount() > 1;
+				long cost = c.cost + (merge ? MERGE_COST : 1);
+				for (int i = 0; i < c.getParentCount(); i++) {
+					NameRevCommit p = (NameRevCommit) walk.parseCommit(c.getParent(i));
+					if (p.tip == null || compare(c.tip, cost, p.tip, p.cost) < 0) {
+						if (merge) {
+							p.tip = c.format().append('^').append(i + 1).toString();
+							p.distance = 0;
+						} else {
+							p.tip = c.tip;
+							p.distance = c.distance + 1;
+						}
+						p.cost = cost;
+						pending.add(p);
+					}
+				}
+			}
+
+			Map<ObjectId, String> result =
+				new LinkedHashMap<ObjectId, String>(revs.size());
+			for (ObjectId id : revs) {
+				RevObject o = walk.parseAny(id);
+				if (o instanceof NameRevCommit) {
+					NameRevCommit c = (NameRevCommit) o;
+					if (c.tip != null)
+						result.put(id, simplify(c.format().toString()));
+				} else {
+					String name = nonCommits.get(id);
+					if (name != null)
+						result.put(id, simplify(name));
+				}
+			}
+
+			setCallable(false);
+			walk.release();
+			return result;
+		} catch (IOException e) {
+			walk.reset();
+			throw new JGitInternalException(e.getMessage(), e);
+		}
+	}
+
+	/**
+	 * Add an object to search for.
+	 *
+	 * @param id
+	 *            object ID to add.
+	 * @return {@code this}
+	 * @throws MissingObjectException
+	 *             the object supplied is not available from the object
+	 *             database.
+	 * @throws JGitInternalException
+	 *             a low-level exception of JGit has occurred. The original
+	 *             exception can be retrieved by calling
+	 *             {@link Exception#getCause()}.
+	 */
+	public NameRevCommand add(ObjectId id) throws MissingObjectException,
+			JGitInternalException {
+		checkCallable();
+		try {
+			walk.parseAny(id);
+		} catch (MissingObjectException e) {
+			throw e;
+		} catch (IOException e) {
+			throw new JGitInternalException(e.getMessage(), e);
+		}
+		revs.add(id.copy());
+		return this;
+	}
+
+	/**
+	 * Add multiple objects to search for.
+	 *
+	 * @param ids
+	 *            object IDs to add.
+	 * @return {@code this}
+	 * @throws MissingObjectException
+	 *             the object supplied is not available from the object
+	 *             database.
+	 * @throws JGitInternalException
+	 *             a low-level exception of JGit has occurred. The original
+	 *             exception can be retrieved by calling
+	 *             {@link Exception#getCause()}.
+	 */
+	public NameRevCommand add(Iterable<ObjectId> ids)
+			throws MissingObjectException, JGitInternalException {
+		for (ObjectId id : ids)
+			add(id);
+		return this;
+	}
+
+	/**
+	 * Add a ref prefix that all results must match.
+	 * <p>
+	 * If an object matches refs under multiple prefixes equally well, the first
+	 * prefix added to this command is preferred.
+	 *
+	 * @param prefix
+	 *            prefix to add; see {@link RefDatabase#getRefs(String)}
+	 * @return {@code this}
+	 */
+	public NameRevCommand addPrefix(String prefix) {
+		checkCallable();
+		prefixes.add(prefix);
+		return this;
+	}
+
+	private void addPrefixes(Map<ObjectId, String> nonCommits,
+			FIFORevQueue pending) throws IOException {
+		if (!prefixes.isEmpty()) {
+			for (String prefix : prefixes)
+				addPrefix(prefix, nonCommits, pending);
+		} else
+			addPrefix(Constants.R_REFS, nonCommits, pending);
+	}
+
+	private void addPrefix(String prefix, Map<ObjectId, String> nonCommits,
+			FIFORevQueue pending) throws IOException {
+		for (Ref ref : repo.getRefDatabase().getRefs(prefix).values()) {
+			if (ref.getObjectId() == null)
+				continue;
+			RevObject o = walk.parseAny(ref.getObjectId());
+			while (o instanceof RevTag) {
+				RevTag t = (RevTag) o;
+				nonCommits.put(o, ref.getName());
+				o = t.getObject();
+				walk.parseHeaders(o);
+			}
+			if (o instanceof NameRevCommit) {
+				NameRevCommit c = (NameRevCommit) o;
+				if (c.tip == null)
+					c.tip = ref.getName();
+				pending.add(c);
+			} else if (!nonCommits.containsKey(o))
+				nonCommits.put(o, ref.getName());
+		}
+	}
+
+	private int minCommitTime() throws IOException {
+		int min = Integer.MAX_VALUE;
+		for (ObjectId id : revs) {
+			RevObject o = walk.parseAny(id);
+			while (o instanceof RevTag) {
+				o = ((RevTag) o).getObject();
+				walk.parseHeaders(o);
+			}
+			if (o instanceof RevCommit) {
+				RevCommit c = (RevCommit) o;
+				if (c.getCommitTime() < min)
+					min = c.getCommitTime();
+			}
+		}
+		return min;
+	}
+
+	private long compare(String leftTip, long leftCost, String rightTip, long rightCost) {
+		long c = leftCost - rightCost;
+		if (c != 0 || prefixes.isEmpty())
+			return c;
+		int li = -1;
+		int ri = -1;
+		for (int i = 0; i < prefixes.size(); i++) {
+			String prefix = prefixes.get(i);
+			if (li < 0 && leftTip.startsWith(prefix))
+				li = i;
+			if (ri < 0 && rightTip.startsWith(prefix))
+				ri = i;
+		}
+		// Don't tiebreak if prefixes are the same, in order to prefer first-parent
+		// paths.
+		return li - ri;
+	}
+
+	private static String simplify(String refName) {
+		if (refName.startsWith(Constants.R_HEADS))
+			return refName.substring(Constants.R_HEADS.length());
+		if (refName.startsWith(Constants.R_TAGS))
+			return refName.substring(Constants.R_TAGS.length());
+		if (refName.startsWith(Constants.R_REFS))
+			return refName.substring(Constants.R_REFS.length());
+		return refName;
+	}
+}