/*
 * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org> 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.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 (RevCommit p : c.parents) {
				p.inDegree++;
				if (firstParent) {
					break;
				}
			}
			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 (RevCommit p : c.parents) {
				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);
				}
				if (firstParent) {
					break;
				}
			}
			return c;
		}
	}
}