/*
    * 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 static org.eclipse.jgit.lib.TypedConfigGetter.UNSET_INT;
  
  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.AbbrevConfig;
  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;
  
  	/**
  	 * The prefix length to use when abbreviating a commit hash.
  	 */
  	private int abbrev = UNSET_INT;
  
  	/**
  	 * 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;
 	}
 
 	/**
 	 * Sets the prefix length to use when abbreviating an object SHA-1.
 	 *
 	 * @param abbrev
 	 *            minimum length of the abbreviated string. Must be in the range
 	 *            [{@value AbbrevConfig#MIN_ABBREV},
 	 *            {@value Constants#OBJECT_ID_STRING_LENGTH}].
 	 * @return {@code this}
 	 * @since 6.1
 	 */
 	public DescribeCommand setAbbrev(int abbrev) {
 		if (abbrev == 0) {
 			this.abbrev = 0;
 		} else {
 			this.abbrev = AbbrevConfig.capAbbrev(abbrev);
 		}
 		return this;
 	}
 
 	private String longDescription(Ref tag, int depth, ObjectId tip)
 			throws IOException {
 		if (abbrev == 0) {
 			return formatRefName(tag.getName());
 		}
 		return String.format("%s-%d-g%s", formatRefName(tag.getName()), //$NON-NLS-1$
 				Integer.valueOf(depth),
 				w.getObjectReader().abbreviate(tip, abbrev).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<>() {
 
 		@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);
 			}
 			if (abbrev == UNSET_INT) {
 				abbrev = AbbrevConfig.parseFromConfig(repo).get();
 			}
 
 			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,
 										AbbrevConfig.capAbbrev(abbrev))
 								.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;
 		}
 	}
 }