/*
 * Copyright (C) 2011, Robin Stocker <robin@nibor.org>
 * Copyright (C) 2012, Matthias Sohn <matthias.sohn@sap.com>
 * 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
 *   copyright notice, this list of conditions and the following
 *   disclaimer in the documentation and/or other materials provided
 *   with the distribution.
 *
 * - Neither the name of the Eclipse Foundation, Inc. nor the
 *   names of its contributors may be used to endorse or promote
 *   products derived from this software without specific prior
 *   written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
 * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.eclipse.jgit.lib;

import java.io.IOException;

import org.eclipse.jgit.revwalk.RevCommit;
import org.eclipse.jgit.revwalk.RevWalk;
import org.eclipse.jgit.revwalk.RevWalkUtils;
import org.eclipse.jgit.revwalk.filter.RevFilter;

/**
 * Status of a branch's relation to its remote-tracking branch.
 */
public class BranchTrackingStatus {

	/**
	 * Compute the tracking status for the <code>branchName</code> in
	 * <code>repository</code>.
	 *
	 * @param repository
	 *            the git repository to compute the status from
	 * @param branchName
	 *            the local branch
	 * @return the tracking status, or null if it is not known
	 * @throws IOException
	 */
	public static BranchTrackingStatus of(Repository repository, String branchName)
			throws IOException {

		String shortBranchName = Repository.shortenRefName(branchName);
		String fullBranchName = Constants.R_HEADS + shortBranchName;
		BranchConfig branchConfig = new BranchConfig(repository.getConfig(),
				shortBranchName);

		String trackingBranch = branchConfig.getTrackingBranch();
		if (trackingBranch == null)
			return null;

		Ref tracking = repository.exactRef(trackingBranch);
		if (tracking == null)
			return null;

		Ref local = repository.exactRef(fullBranchName);
		if (local == null)
			return null;

		RevWalk walk = new RevWalk(repository);

		RevCommit localCommit = walk.parseCommit(local.getObjectId());
		RevCommit trackingCommit = walk.parseCommit(tracking.getObjectId());

		walk.setRevFilter(RevFilter.MERGE_BASE);
		walk.markStart(localCommit);
		walk.markStart(trackingCommit);
		RevCommit mergeBase = walk.next();

		walk.reset();
		walk.setRevFilter(RevFilter.ALL);
		int aheadCount = RevWalkUtils.count(walk, localCommit, mergeBase);
		int behindCount = RevWalkUtils.count(walk, trackingCommit, mergeBase);

		return new BranchTrackingStatus(trackingBranch, aheadCount, behindCount);
	}

	private final String remoteTrackingBranch;

	private final int aheadCount;

	private final int behindCount;

	private BranchTrackingStatus(String remoteTrackingBranch, int aheadCount,
			int behindCount) {
		this.remoteTrackingBranch = remoteTrackingBranch;
		this.aheadCount = aheadCount;
		this.behindCount = behindCount;
	}

	/**
	 * @return full remote-tracking branch name
	 */
	public String getRemoteTrackingBranch() {
		return remoteTrackingBranch;
	}

	/**
	 * @return number of commits that the local branch is ahead of the
	 *         remote-tracking branch
	 */
	public int getAheadCount() {
		return aheadCount;
	}

	/**
	 * @return number of commits that the local branch is behind of the
	 *         remote-tracking branch
	 */
	public int getBehindCount() {
		return behindCount;
	}
}