/*
 * Copyright (C) 2009, Google Inc.
 * 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;
import org.eclipse.jgit.errors.StopWalkException;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.revwalk.filter.RevFilter;

Default (and first pass) RevCommit Generator implementation for RevWalk.
 This generator starts from a set of one or more commits and process them in descending (newest to oldest) commit time order. Commits automatically cause their parents to be enqueued for further processing, allowing the entire commit graph to be walked. A RevFilter may be used to select a subset of the commits and return them to the caller. /**
 * Default (and first pass) RevCommit Generator implementation for RevWalk.
 * <p>
 * This generator starts from a set of one or more commits and process them in
 * descending (newest to oldest) commit time order. Commits automatically cause
 * their parents to be enqueued for further processing, allowing the entire
 * commit graph to be walked. A {@link RevFilter} may be used to select a subset
 * of the commits and return them to the caller.
 */
class PendingGenerator extends Generator {
	private static final int PARSED = RevWalk.PARSED;

	private static final int SEEN = RevWalk.SEEN;

	private static final int UNINTERESTING = RevWalk.UNINTERESTING;

	
Number of additional commits to scan after we think we are done.

This small buffer of commits is scanned to ensure we didn't miss anything
as a result of clock skew when the commits were made. We need to set our
constant to 1 additional commit due to the use of a pre-increment
operator when accessing the value.
/**
	 * Number of additional commits to scan after we think we are done.
	 * <p>
	 * This small buffer of commits is scanned to ensure we didn't miss anything
	 * as a result of clock skew when the commits were made. We need to set our
	 * constant to 1 additional commit due to the use of a pre-increment
	 * operator when accessing the value.
	 */
	static final int OVER_SCAN = 5 + 1;

	
A commit near the end of time, to initialize last with. /** A commit near the end of time, to initialize {@link #last} with. */
	private static final RevCommit INIT_LAST;

	static {
		INIT_LAST = new RevCommit(ObjectId.zeroId());
		INIT_LAST.commitTime = Integer.MAX_VALUE;
	}

	private final RevWalk walker;

	private final DateRevQueue pending;

	private final RevFilter filter;

	private final int output;

	
Last commit produced to the caller from next(). /** Last commit produced to the caller from {@link #next()}. */
	private RevCommit last = INIT_LAST;

	
Number of commits we have remaining in our over-scan allotment.
 Only relevant if there are UNINTERESTING commits in the pending queue. /**
	 * Number of commits we have remaining in our over-scan allotment.
	 * <p>
	 * Only relevant if there are {@link #UNINTERESTING} commits in the
	 * {@link #pending} queue.
	 */
	private int overScan = OVER_SCAN;

	boolean canDispose;

	PendingGenerator(final RevWalk w, final DateRevQueue p,
			final RevFilter f, final int out) {
		super(w.isFirstParent());
		walker = w;
		pending = p;
		filter = f;
		output = out;
		canDispose = true;
	}

	@Override
	int outputType() {
		return output | SORT_COMMIT_TIME_DESC;
	}

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

				final boolean produce;
				if ((c.flags & UNINTERESTING) != 0)
					produce = false;
				else {
					if (filter.requiresCommitBody())
						c.parseBody(walker);
					produce = filter.include(walker, c);
				}

				for (int i = 0; i < c.parents.length; i++) {
					RevCommit p = c.parents[i];
					// If the commit is uninteresting, don't try to prune
					// parents because we want the maximal uninteresting set.
					if (firstParent && i > 0 && (c.flags & UNINTERESTING) == 0) {
						continue;
					}
					if ((p.flags & SEEN) != 0)
						continue;
					if ((p.flags & PARSED) == 0)
						p.parseHeaders(walker);
					p.flags |= SEEN;
					pending.add(p);
				}
				walker.carryFlagsImpl(c);

				if ((c.flags & UNINTERESTING) != 0) {
					if (pending.everbodyHasFlag(UNINTERESTING)) {
						final RevCommit n = pending.peek();
						if (n != null && n.commitTime >= last.commitTime) {
							// This is too close to call. The next commit we
							// would pop is dated after the last one produced.
							// We have to keep going to ensure that we carry
							// flags as much as necessary.
							//
							overScan = OVER_SCAN;
						} else if (--overScan == 0)
							throw StopWalkException.INSTANCE;
					} else {
						overScan = OVER_SCAN;
					}
					if (canDispose)
						c.disposeBody();
					continue;
				}

				if (produce)
					return last = c;
				else if (canDispose)
					c.disposeBody();
			}
		} catch (StopWalkException swe) {
			pending.clear();
			return null;
		}
	}
}