DescribeCommand.java

/*
 * Copyright (C) 2013, CloudBees, Inc. and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */
package org.eclipse.jgit.api;

import static org.eclipse.jgit.lib.Constants.R_REFS;
import static org.eclipse.jgit.lib.Constants.R_TAGS;

import java.io.IOException;
import java.text.MessageFormat;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.Date;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import org.eclipse.jgit.api.errors.GitAPIException;
import org.eclipse.jgit.api.errors.JGitInternalException;
import org.eclipse.jgit.api.errors.RefNotFoundException;
import org.eclipse.jgit.errors.IncorrectObjectTypeException;
import org.eclipse.jgit.errors.InvalidPatternException;
import org.eclipse.jgit.errors.MissingObjectException;
import org.eclipse.jgit.fnmatch.FileNameMatcher;
import org.eclipse.jgit.internal.JGitText;
import org.eclipse.jgit.lib.Constants;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.Ref;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.revwalk.RevCommit;
import org.eclipse.jgit.revwalk.RevFlag;
import org.eclipse.jgit.revwalk.RevFlagSet;
import org.eclipse.jgit.revwalk.RevTag;
import org.eclipse.jgit.revwalk.RevWalk;

/**
 * Given a commit, show the most recent tag that is reachable from a commit.
 *
 * @since 3.2
 */
public class DescribeCommand extends GitCommand<String> {
    private final RevWalk w;

    /**
     * Commit to describe.
     */
    private RevCommit target;

    /**
     * How many tags we'll consider as candidates.
     * This can only go up to the number of flags JGit can support in a walk,
     * which is 24.
     */
    private int maxCandidates = 10;

    /**
     * Whether to always use long output format or not.
     */
    private boolean longDesc;

    /**
     * Pattern matchers to be applied to tags under consideration.
     */
    private List<FileNameMatcher> matchers = new ArrayList<>();

    /**
     * Whether to use all refs in the refs/ namespace
     */
    private boolean useAll;

    /**
     * Whether to use all tags (incl. lightweight) or not.
     */
    private boolean useTags;

    /**
     * Whether to show a uniquely abbreviated commit hash as a fallback or not.
     */
    private boolean always;

    /**
     * Constructor for DescribeCommand.
     *
     * @param repo
     *            the {@link org.eclipse.jgit.lib.Repository}
     */
    protected DescribeCommand(Repository repo) {
        super(repo);
        w = new RevWalk(repo);
        w.setRetainBody(false);
    }

    /**
     * Sets the commit to be described.
     *
     * @param target
     *      A non-null object ID to be described.
     * @return {@code this}
     * @throws MissingObjectException
     *             the supplied commit does not exist.
     * @throws IncorrectObjectTypeException
     *             the supplied id is not a commit or an annotated tag.
     * @throws java.io.IOException
     *             a pack file or loose object could not be read.
     */
    public DescribeCommand setTarget(ObjectId target) throws IOException {
        this.target = w.parseCommit(target);
        return this;
    }

    /**
     * Sets the commit to be described.
     *
     * @param rev
     *            Commit ID, tag, branch, ref, etc. See
     *            {@link org.eclipse.jgit.lib.Repository#resolve(String)} for
     *            allowed syntax.
     * @return {@code this}
     * @throws IncorrectObjectTypeException
     *             the supplied id is not a commit or an annotated tag.
     * @throws org.eclipse.jgit.api.errors.RefNotFoundException
     *             the given rev didn't resolve to any object.
     * @throws java.io.IOException
     *             a pack file or loose object could not be read.
     */
    public DescribeCommand setTarget(String rev) throws IOException,
            RefNotFoundException {
        ObjectId id = repo.resolve(rev);
        if (id == null)
            throw new RefNotFoundException(MessageFormat.format(JGitText.get().refNotResolved, rev));
        return setTarget(id);
    }

    /**
     * Determine whether always to use the long format or not. When set to
     * <code>true</code> the long format is used even the commit matches a tag.
     *
     * @param longDesc
     *            <code>true</code> if always the long format should be used.
     * @return {@code this}
     * @see <a
     *      href="https://www.kernel.org/pub/software/scm/git/docs/git-describe.html"
     *      >Git documentation about describe</a>
     * @since 4.0
     */
    public DescribeCommand setLong(boolean longDesc) {
        this.longDesc = longDesc;
        return this;
    }

    /**
     * Instead of using only the annotated tags, use any ref found in refs/
     * namespace. This option enables matching any known branch,
     * remote-tracking branch, or lightweight tag.
     *
     * @param all
     *            <code>true</code> enables matching any ref found in refs/
     *            like setting option --all in c git
     * @return {@code this}
     * @since 5.10
     */
    public DescribeCommand setAll(boolean all) {
        this.useAll = all;
        return this;
    }

    /**
     * Instead of using only the annotated tags, use any tag found in refs/tags
     * namespace. This option enables matching lightweight (non-annotated) tags
     * or not.
     *
     * @param tags
     *            <code>true</code> enables matching lightweight (non-annotated)
     *            tags like setting option --tags in c git
     * @return {@code this}
     * @since 5.0
     */
    public DescribeCommand setTags(boolean tags) {
        this.useTags = tags;
        return this;
    }

    /**
     * Always describe the commit by eventually falling back to a uniquely
     * abbreviated commit hash if no other name matches.
     *
     * @param always
     *            <code>true</code> enables falling back to a uniquely
     *            abbreviated commit hash
     * @return {@code this}
     * @since 5.4
     */
    public DescribeCommand setAlways(boolean always) {
        this.always = always;
        return this;
    }

    private String longDescription(Ref tag, int depth, ObjectId tip)
            throws IOException {
        return String.format(
                "%s-%d-g%s", formatRefName(tag.getName()), //$NON-NLS-1$
                Integer.valueOf(depth), w.getObjectReader().abbreviate(tip)
                        .name());
    }

    /**
     * Sets one or more {@code glob(7)} patterns that tags must match to be
     * considered. If multiple patterns are provided, tags only need match one
     * of them.
     *
     * @param patterns
     *            the {@code glob(7)} pattern or patterns
     * @return {@code this}
     * @throws org.eclipse.jgit.errors.InvalidPatternException
     *             if the pattern passed in was invalid.
     * @see <a href=
     *      "https://www.kernel.org/pub/software/scm/git/docs/git-describe.html"
     *      >Git documentation about describe</a>
     * @since 4.9
     */
    public DescribeCommand setMatch(String... patterns) throws InvalidPatternException {
        for (String p : patterns) {
            matchers.add(new FileNameMatcher(p, null));
        }
        return this;
    }

    private final Comparator<Ref> TAG_TIE_BREAKER = new Comparator<Ref>() {

        @Override
        public int compare(Ref o1, Ref o2) {
            try {
                return tagDate(o2).compareTo(tagDate(o1));
            } catch (IOException e) {
                return 0;
            }
        }

        private Date tagDate(Ref tag) throws IOException {
            RevTag t = w.parseTag(tag.getObjectId());
            w.parseBody(t);
            return t.getTaggerIdent().getWhen();
        }
    };

    private Optional<Ref> getBestMatch(List<Ref> tags) {
        if (tags == null || tags.isEmpty()) {
            return Optional.empty();
        } else if (matchers.isEmpty()) {
            Collections.sort(tags, TAG_TIE_BREAKER);
            return Optional.of(tags.get(0));
        } else {
            // Find the first tag that matches in the stream of all tags
            // filtered by matchers ordered by tie break order
            Stream<Ref> matchingTags = Stream.empty();
            for (FileNameMatcher matcher : matchers) {
                Stream<Ref> m = tags.stream().filter(
                        tag -> {
                            matcher.append(formatRefName(tag.getName()));
                            boolean result = matcher.isMatch();
                            matcher.reset();
                            return result;
                        });
                matchingTags = Stream.of(matchingTags, m).flatMap(i -> i);
            }
            return matchingTags.sorted(TAG_TIE_BREAKER).findFirst();
        }
    }

    private ObjectId getObjectIdFromRef(Ref r) throws JGitInternalException {
        try {
            ObjectId key = repo.getRefDatabase().peel(r).getPeeledObjectId();
            if (key == null) {
                key = r.getObjectId();
            }
            return key;
        } catch (IOException e) {
            throw new JGitInternalException(e.getMessage(), e);
        }
    }

    /**
     * {@inheritDoc}
     * <p>
     * Describes the specified commit. Target defaults to HEAD if no commit was
     * set explicitly.
     */
    @Override
    public String call() throws GitAPIException {
        try {
            checkCallable();
            if (target == null) {
                setTarget(Constants.HEAD);
            }

            Collection<Ref> tagList = repo.getRefDatabase()
                    .getRefsByPrefix(useAll ? R_REFS : R_TAGS);
            Map<ObjectId, List<Ref>> tags = tagList.stream()
                    .filter(this::filterLightweightTags)
                    .collect(Collectors.groupingBy(this::getObjectIdFromRef));

            // combined flags of all the candidate instances
            final RevFlagSet allFlags = new RevFlagSet();

            /**
             * Tracks the depth of each tag as we find them.
             */
            class Candidate {
                final Ref tag;
                final RevFlag flag;

                /**
                 * This field counts number of commits that are reachable from
                 * the tip but not reachable from the tag.
                 */
                int depth;

                Candidate(RevCommit commit, Ref tag) {
                    this.tag = tag;
                    this.flag = w.newFlag(tag.getName());
                    // we'll mark all the nodes reachable from this tag accordingly
                    allFlags.add(flag);
                    w.carry(flag);
                    commit.add(flag);
                    // As of this writing, JGit carries a flag from a child to its parents
                    // right before RevWalk.next() returns, so all the flags that are added
                    // must be manually carried to its parents. If that gets fixed,
                    // this will be unnecessary.
                    commit.carry(flag);
                }

                /**
                 * Does this tag contain the given commit?
                 */
                boolean reaches(RevCommit c) {
                    return c.has(flag);
                }

                String describe(ObjectId tip) throws IOException {
                    return longDescription(tag, depth, tip);
                }

            }
            List<Candidate> candidates = new ArrayList<>();    // all the candidates we find

            // is the target already pointing to a suitable tag? if so, we are done!
            Optional<Ref> bestMatch = getBestMatch(tags.get(target));
            if (bestMatch.isPresent()) {
                return longDesc ? longDescription(bestMatch.get(), 0, target) :
                        formatRefName(bestMatch.get().getName());
            }

            w.markStart(target);

            int seen = 0;   // commit seen thus far
            RevCommit c;
            while ((c = w.next()) != null) {
                if (!c.hasAny(allFlags)) {
                    // if a tag already dominates this commit,
                    // then there's no point in picking a tag on this commit
                    // since the one that dominates it is always more preferable
                    bestMatch = getBestMatch(tags.get(c));
                    if (bestMatch.isPresent()) {
                        Candidate cd = new Candidate(c, bestMatch.get());
                        candidates.add(cd);
                        cd.depth = seen;
                    }
                }

                // if the newly discovered commit isn't reachable from a tag that we've seen
                // it counts toward the total depth.
                for (Candidate cd : candidates) {
                    if (!cd.reaches(c))
                        cd.depth++;
                }

                // if we have search going for enough tags, we will start
                // closing down. JGit can only give us a finite number of bits,
                // so we can't track all tags even if we wanted to.
                if (candidates.size() >= maxCandidates)
                    break;

                // TODO: if all the commits in the queue of RevWalk has allFlags
                // there's no point in continuing search as we'll not discover any more
                // tags. But RevWalk doesn't expose this.
                seen++;
            }

            // at this point we aren't adding any more tags to our search,
            // but we still need to count all the depths correctly.
            while ((c = w.next()) != null) {
                if (c.hasAll(allFlags)) {
                    // no point in visiting further from here, so cut the search here
                    for (RevCommit p : c.getParents())
                        p.add(RevFlag.SEEN);
                } else {
                    for (Candidate cd : candidates) {
                        if (!cd.reaches(c))
                            cd.depth++;
                    }
                }
            }

            // if all the nodes are dominated by all the tags, the walk stops
            if (candidates.isEmpty()) {
                return always ? w.getObjectReader().abbreviate(target).name() : null;
            }

            Candidate best = Collections.min(candidates,
                    (Candidate o1, Candidate o2) -> o1.depth - o2.depth);

            return best.describe(target);
        } catch (IOException e) {
            throw new JGitInternalException(e.getMessage(), e);
        } finally {
            setCallable(false);
            w.close();
        }
    }

    /**
     * Removes the refs/ or refs/tags prefix from tag names
     * @param name the name of the tag
     * @return the tag name with its prefix removed
     */
    private String formatRefName(String name) {
        return name.startsWith(R_TAGS) ? name.substring(R_TAGS.length()) :
                name.substring(R_REFS.length());
    }

    /**
     * Whether we use lightweight tags or not for describe Candidates
     *
     * @param ref
     *            reference under inspection
     * @return true if it should be used for describe or not regarding
     *         {@link org.eclipse.jgit.api.DescribeCommand#useTags}
     */
    @SuppressWarnings("null")
    private boolean filterLightweightTags(Ref ref) {
        ObjectId id = ref.getObjectId();
        try {
            return this.useAll || this.useTags || (id != null && (w.parseTag(id) != null));
        } catch (IOException e) {
            return false;
        }
    }
}