/*
 * 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;

abstract class BlockRevQueue extends AbstractRevQueue {
	protected BlockFreeList free;

	
Create an empty revision queue.
Params:
firstParent – 
           whether only first-parent links should be followed when
           walking/**
	 * Create an empty revision queue.
	 *
	 * @param firstParent
	 *            whether only first-parent links should be followed when
	 *            walking
	 */
	protected BlockRevQueue(boolean firstParent) {
		super(firstParent);
		free = new BlockFreeList();
	}

	BlockRevQueue(Generator s) throws MissingObjectException,
			IncorrectObjectTypeException, IOException {
		super(s.firstParent);
		free = new BlockFreeList();
		outputType = s.outputType();
		s.shareFreeList(this);
		for (;;) {
			final RevCommit c = s.next();
			if (c == null)
				break;
			add(c);
		}
	}

	
{@inheritDoc}

Reconfigure this queue to share the same free list as another.

Multiple revision queues can be connected to the same free list, making
it less expensive for applications to shuttle commits between them. This
method arranges for the receiver to take from / return to the same free
list as the supplied queue.

Free lists are not thread-safe. Applications must ensure that all queues
sharing the same free list are doing so from only a single thread.
/**
	 * {@inheritDoc}
	 * <p>
	 * Reconfigure this queue to share the same free list as another.
	 * <p>
	 * Multiple revision queues can be connected to the same free list, making
	 * it less expensive for applications to shuttle commits between them. This
	 * method arranges for the receiver to take from / return to the same free
	 * list as the supplied queue.
	 * <p>
	 * Free lists are not thread-safe. Applications must ensure that all queues
	 * sharing the same free list are doing so from only a single thread.
	 */
	@Override
	public void shareFreeList(BlockRevQueue q) {
		free = q.free;
	}

	static final class BlockFreeList {
		private Block next;

		Block newBlock() {
			Block b = next;
			if (b == null)
				return new Block();
			next = b.next;
			b.clear();
			return b;
		}

		void freeBlock(Block b) {
			b.next = next;
			next = b;
		}

		void clear() {
			next = null;
		}
	}

	static final class Block {
		static final int BLOCK_SIZE = 256;

		
Next block in our chain of blocks; null if we are the last. /** Next block in our chain of blocks; null if we are the last. */
		Block next;

		
Our table of queued commits. /** Our table of queued commits. */
		final RevCommit[] commits = new RevCommit[BLOCK_SIZE];

		
Next valid entry in commits. /** Next valid entry in {@link #commits}. */
		int headIndex;

		
Next free entry in commits for addition at. /** Next free entry in {@link #commits} for addition at. */
		int tailIndex;

		boolean isFull() {
			return tailIndex == BLOCK_SIZE;
		}

		boolean isEmpty() {
			return headIndex == tailIndex;
		}

		boolean canUnpop() {
			return headIndex > 0;
		}

		void add(RevCommit c) {
			commits[tailIndex++] = c;
		}

		void unpop(RevCommit c) {
			commits[--headIndex] = c;
		}

		RevCommit pop() {
			return commits[headIndex++];
		}

		RevCommit peek() {
			return commits[headIndex];
		}

		void clear() {
			next = null;
			headIndex = 0;
			tailIndex = 0;
		}

		void resetToMiddle() {
			headIndex = tailIndex = BLOCK_SIZE / 2;
		}

		void resetToEnd() {
			headIndex = tailIndex = BLOCK_SIZE;
		}
	}
}