/*
    * Copyright (C) 2013, CloudBees, 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
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   *   with the distribution.
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   * - Neither the name of the Eclipse Foundation, Inc. nor the
   *   names of its contributors may be used to endorse or promote
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  package org.eclipse.jgit.api;
  
  import static org.eclipse.jgit.lib.Constants.R_TAGS;
  
  import java.io.IOException;
  import java.text.MessageFormat;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.Comparator;
  import java.util.HashMap;
  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.api.errors.RefNotFoundException;
  import org.eclipse.jgit.errors.IncorrectObjectTypeException;
  import org.eclipse.jgit.errors.MissingObjectException;
  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.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;
  
  	/**
  	 *
  	 * @param repo
  	 */
 	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 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 Repository#resolve(String)} for allowed syntax.
 	 * @return {@code this}
 	 * @throws IncorrectObjectTypeException
 	 *             the supplied id is not a commit or an annotated tag.
 	 * @throws RefNotFoundException
 	 * 				the given rev didn't resolve to any object.
 	 * @throws 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;
 	}
 
 	private String longDescription(Ref tag, int depth, ObjectId tip)
 			throws IOException {
 		return String.format(
 				"%s-%d-g%s", tag.getName().substring(R_TAGS.length()), //$NON-NLS-1$
 				Integer.valueOf(depth), w.getObjectReader().abbreviate(tip)
 						.name());
 	}
 
 	/**
 	 * Describes the specified commit. Target defaults to HEAD if no commit was
 	 * set explicitly.
 	 *
 	 * @return if there's a tag that points to the commit being described, this
 	 *         tag name is returned. Otherwise additional suffix is added to the
 	 *         nearest tag, just like git-describe(1).
 	 *         <p>
 	 *         If none of the ancestors of the commit being described has any
 	 *         tags at all, then this method returns null, indicating that
 	 *         there's no way to describe this tag.
 	 */
 	@Override
 	public String call() throws GitAPIException {
 		try {
 			checkCallable();
 
 			if (target == null)
 				setTarget(Constants.HEAD);
 
 			Map<ObjectId, Ref> tags = new HashMap<ObjectId, Ref>();
 
 			for (Ref r : repo.getRefDatabase().getRefs(R_TAGS).values()) {
 				ObjectId key = repo.peel(r).getPeeledObjectId();
 				if (key == null)
 					key = r.getObjectId();
 				tags.put(key, r);
 			}
 
 			// 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<Candidate>();    // all the candidates we find
 
 			// is the target already pointing to a tag? if so, we are done!
 			Ref lucky = tags.get(target);
 			if (lucky != null) {
 				return longDesc ? longDescription(lucky, 0, target) : lucky
 						.getName().substring(R_TAGS.length());
 			}
 
 			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
 					Ref t = tags.get(c);
 					if (t != null) {
 						Candidate cd = new Candidate(c, t);
 						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 null;
 
 			Candidate best = Collections.min(candidates, new Comparator<Candidate>() {
 				public int compare(Candidate o1, Candidate o2) {
 					return o1.depth - o2.depth;
 				}
 			});
 
 			return best.describe(target);
 		} catch (IOException e) {
 			throw new JGitInternalException(e.getMessage(), e);
 		} finally {
 			setCallable(false);
 			w.close();
 		}
 	}
 }