/*
 * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
 * 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.revwalk;

import java.io.IOException;

import org.eclipse.jgit.errors.IncorrectObjectTypeException;
import org.eclipse.jgit.errors.MissingObjectException;

Sorts commits in topological order. /** Sorts commits in topological order. */
class TopoSortGenerator extends Generator {
	private static final int TOPO_DELAY = RevWalk.TOPO_DELAY;

	private final FIFORevQueue pending;

	private final int outputType;

	
Create a new sorter and completely spin the generator.

When the constructor completes the supplied generator will have no
commits remaining, as all of the commits will be held inside of this
generator's internal buffer.
Params:
s – 
           generator to pull all commits out of, and into this buffer.
Throws:
MissingObjectException – 
IncorrectObjectTypeException – 
IOException – /**
	 * Create a new sorter and completely spin the generator.
	 * <p>
	 * When the constructor completes the supplied generator will have no
	 * commits remaining, as all of the commits will be held inside of this
	 * generator's internal buffer.
	 *
	 * @param s
	 *            generator to pull all commits out of, and into this buffer.
	 * @throws MissingObjectException
	 * @throws IncorrectObjectTypeException
	 * @throws IOException
	 */
	TopoSortGenerator(Generator s) throws MissingObjectException,
			IncorrectObjectTypeException, IOException {
		super(s.firstParent);
		pending = new FIFORevQueue(firstParent);
		outputType = s.outputType() | SORT_TOPO;
		s.shareFreeList(pending);
		for (;;) {
			final RevCommit c = s.next();
			if (c == null) {
				break;
			}
			for (int i = 0; i < c.parents.length; i++) {
				if (firstParent && i > 0) {
					break;
				}
				c.parents[i].inDegree++;
			}
			pending.add(c);
		}
	}

	@Override
	int outputType() {
		return outputType;
	}

	@Override
	void shareFreeList(BlockRevQueue q) {
		q.shareFreeList(pending);
	}

	@Override
	RevCommit next() throws MissingObjectException,
			IncorrectObjectTypeException, IOException {
		for (;;) {
			final RevCommit c = pending.next();
			if (c == null)
				return null;

			if (c.inDegree > 0) {
				// At least one of our children is missing. We delay
				// production until all of our children are output.
				//
				c.flags |= TOPO_DELAY;
				continue;
			}

			// All of our children have already produced,
			// so it is OK for us to produce now as well.
			//
			for (int i = 0; i < c.parents.length; i++) {
				if (firstParent && i > 0) {
					break;
				}
				RevCommit p = c.parents[i];
				if (--p.inDegree == 0 && (p.flags & TOPO_DELAY) != 0) {
					// This parent tried to come before us, but we are
					// his last child. unpop the parent so it goes right
					// behind this child.
					//
					p.flags &= ~TOPO_DELAY;
					pending.unpop(p);
				}
			}
			return c;
		}
	}
}