/*
 * 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 Also:
Git documentation about name-rev
Since:
3.0/**
 * 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. /** 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. /** 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.
Params:
repo –  the Repository/**
	 * 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} /** {@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.
Params:
id – 
           object ID to add.
Throws:
MissingObjectException – 
            the object supplied is not available from the object
            database.
JGitInternalException –  a low-level exception of JGit has occurred. The original exception can be retrieved by calling Throwable.getCause().
Returns:
this/**
	 * 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.
Params:
ids – 
           object IDs to add.
Throws:
MissingObjectException – 
            the object supplied is not available from the object
            database.
JGitInternalException –  a low-level exception of JGit has occurred. The original exception can be retrieved by calling Throwable.getCause().
Returns:
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.
 If an object matches multiple refs equally well, the first matching ref added with addRef(Ref) is preferred, or else the first matching prefix added by addPrefix(String). 
Params:
prefix – 
           prefix to add; the prefix must end with a slash
Returns:
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 refs/tags/ to the set that all results must match. 
 Calls addRef(Ref); see that method for a note on matching priority. 
Throws:
JGitInternalException –  a low-level exception of JGit has occurred. The original exception can be retrieved by calling Throwable.getCause().
Returns:
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.
 If an object matches multiple refs equally well, the first matching ref added with addRef(Ref) is preferred, or else the first matching prefix added by addPrefix(String). 
Params:
ref – 
           ref to add.
Returns:
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;
	}
}