/*
    * Copyright (C) 2013, Google 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 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.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>
   * @since 3.0
   */
  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((Object) 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;
  	private List<Ref> refs;
  	private int mergeCost;
  
  	/**
  	 * Create a new name-rev command.
  	 *
  	 * @param repo
  	 *            the {@link org.eclipse.jgit.lib.Repository}
  	 */
  	protected NameRevCommand(Repository repo) {
  		super(repo);
  		mergeCost = MERGE_COST;
  		prefixes = new ArrayList<>(2);
  		revs = new ArrayList<>(2);
  		walk = new RevWalk(repo) {
  			@Override
  			public NameRevCommit createCommit(AnyObjectId id) {
  				return new NameRevCommit(id);
 			}
 		};
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public Map<ObjectId, String> call() throws GitAPIException {
 		try {
 			Map<ObjectId, String> nonCommits = new HashMap<>();
 			FIFORevQueue pending = new FIFORevQueue();
 			if (refs != null) {
 				for (Ref ref : refs)
 					addRef(ref, nonCommits, pending);
 			}
 			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;
 				for (int i = 0; i < c.getParentCount(); i++) {
 					NameRevCommit p = (NameRevCommit) walk.parseCommit(c.getParent(i));
 					long cost = c.cost + (i > 0 ? mergeCost : 1);
 					if (p.tip == null || compare(c.tip, cost, p.tip, p.cost) < 0) {
 						if (i > 0) {
 							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<>(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);
 			return result;
 		} catch (IOException e) {
 			throw new JGitInternalException(e.getMessage(), e);
 		} finally {
 			walk.close();
 		}
 	}
 
 	/**
 	 * Add an object to search for.
 	 *
 	 * @param id
 	 *            object ID to add.
 	 * @return {@code this}
 	 * @throws org.eclipse.jgit.errors.MissingObjectException
 	 *             the object supplied is not available from the object
 	 *             database.
 	 * @throws org.eclipse.jgit.api.errors.JGitInternalException
 	 *             a low-level exception of JGit has occurred. The original
 	 *             exception can be retrieved by calling
 	 *             {@link java.lang.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 org.eclipse.jgit.errors.MissingObjectException
 	 *             the object supplied is not available from the object
 	 *             database.
 	 * @throws org.eclipse.jgit.api.errors.JGitInternalException
 	 *             a low-level exception of JGit has occurred. The original
 	 *             exception can be retrieved by calling
 	 *             {@link java.lang.Exception#getCause()}.
 	 */
 	public NameRevCommand add(Iterable<ObjectId> ids)
 			throws MissingObjectException, JGitInternalException {
 		for (ObjectId id : ids)
 			add(id);
 		return this;
 	}
 
 	/**
 	 * Add a ref prefix to the set that results must match.
 	 * <p>
 	 * If an object matches multiple refs equally well, the first matching ref
 	 * added with {@link #addRef(Ref)} is preferred, or else the first matching
 	 * prefix added by {@link #addPrefix(String)}.
 	 *
 	 * @param prefix
 	 *            prefix to add; the prefix must end with a slash
 	 * @return {@code this}
 	 */
 	public NameRevCommand addPrefix(String prefix) {
 		checkCallable();
 		prefixes.add(prefix);
 		return this;
 	}
 
 	/**
 	 * Add all annotated tags under {@code refs/tags/} to the set that all
 	 * results must match.
 	 * <p>
 	 * Calls {@link #addRef(Ref)}; see that method for a note on matching
 	 * priority.
 	 *
 	 * @return {@code this}
 	 * @throws JGitInternalException
 	 *             a low-level exception of JGit has occurred. The original
 	 *             exception can be retrieved by calling
 	 *             {@link java.lang.Exception#getCause()}.
 	 */
 	public NameRevCommand addAnnotatedTags() {
 		checkCallable();
 		if (refs == null)
 			refs = new ArrayList<>();
 		try {
 			for (Ref ref : repo.getRefDatabase()
 					.getRefsByPrefix(Constants.R_TAGS)) {
 				ObjectId id = ref.getObjectId();
 				if (id != null && (walk.parseAny(id) instanceof RevTag))
 					addRef(ref);
 			}
 		} catch (IOException e) {
 			throw new JGitInternalException(e.getMessage(), e);
 		}
 		return this;
 	}
 
 	/**
 	 * Add a ref to the set that all results must match.
 	 * <p>
 	 * If an object matches multiple refs equally well, the first matching ref
 	 * added with {@link #addRef(Ref)} is preferred, or else the first matching
 	 * prefix added by {@link #addPrefix(String)}.
 	 *
 	 * @param ref
 	 *            ref to add.
 	 * @return {@code this}
 	 */
 	public NameRevCommand addRef(Ref ref) {
 		checkCallable();
 		if (refs == null)
 			refs = new ArrayList<>();
 		refs.add(ref);
 		return this;
 	}
 
 	NameRevCommand setMergeCost(int cost) {
 		mergeCost = cost;
 		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 if (refs == null)
 			addPrefix(Constants.R_REFS, nonCommits, pending);
 	}
 
 	private void addPrefix(String prefix, Map<ObjectId, String> nonCommits,
 			FIFORevQueue pending) throws IOException {
 		for (Ref ref : repo.getRefDatabase().getRefsByPrefix(prefix))
 			addRef(ref, nonCommits, pending);
 	}
 
 	private void addRef(Ref ref, Map<ObjectId, String> nonCommits,
 			FIFORevQueue pending) throws IOException {
 		if (ref.getObjectId() == null)
 			return;
 		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;
 	}
 }