/*
    * 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;
  
  /**
   * A queue of commits in FIFO order.
   */
  public class FIFORevQueue extends BlockRevQueue {
  	private Block head;
  
  	private Block tail;
  
  	/** Create an empty FIFO queue. */
  	public FIFORevQueue() {
  		super(false);
  	}
  
  	FIFORevQueue(boolean firstParent) {
  		super(firstParent);
  	}
  
  	FIFORevQueue(Generator s) throws MissingObjectException,
  			IncorrectObjectTypeException, IOException {
  		super(s);
  	}
  
  	/** {@inheritDoc} */
  	@Override
  	public void add(RevCommit c) {
  		Block b = tail;
  		if (b == null) {
  			b = free.newBlock();
  			b.add(c);
  			head = b;
  			tail = b;
  			return;
  		} else if (b.isFull()) {
  			b = free.newBlock();
  			tail.next = b;
  			tail = b;
  		}
  		b.add(c);
  	}
  
  	/**
  	 * Insert the commit pointer at the front of the queue.
  	 *
  	 * @param c
  	 *            the commit to insert into the queue.
  	 */
  	public void unpop(RevCommit c) {
  		Block b = head;
  		if (b == null) {
  			b = free.newBlock();
  			b.resetToMiddle();
  			b.add(c);
  			head = b;
  			tail = b;
  			return;
  		} else if (b.canUnpop()) {
  			b.unpop(c);
  			return;
  		}
  
  		b = free.newBlock();
  		b.resetToEnd();
  		b.unpop(c);
  		b.next = head;
  		head = b;
  	}
  
  	/** {@inheritDoc} */
  	@Override
  	public RevCommit next() {
  		final Block b = head;
  		if (b == null)
  			return null;
  
  		final RevCommit c = b.pop();
  		if (b.isEmpty()) {
  			head = b.next;
  			if (head == null)
  				tail = null;
  			free.freeBlock(b);
  		}
  		return c;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public void clear() {
 		head = null;
 		tail = null;
 		free.clear();
 	}
 
 	@Override
 	boolean everbodyHasFlag(int f) {
 		for (Block b = head; b != null; b = b.next) {
 			for (int i = b.headIndex; i < b.tailIndex; i++)
 				if ((b.commits[i].flags & f) == 0)
 					return false;
 		}
 		return true;
 	}
 
 	@Override
 	boolean anybodyHasFlag(int f) {
 		for (Block b = head; b != null; b = b.next) {
 			for (int i = b.headIndex; i < b.tailIndex; i++)
 				if ((b.commits[i].flags & f) != 0)
 					return true;
 		}
 		return false;
 	}
 
 	void removeFlag(int f) {
 		final int not_f = ~f;
 		for (Block b = head; b != null; b = b.next) {
 			for (int i = b.headIndex; i < b.tailIndex; i++)
 				b.commits[i].flags &= not_f;
 		}
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public String toString() {
 		final StringBuilder s = new StringBuilder();
 		for (Block q = head; q != null; q = q.next) {
 			for (int i = q.headIndex; i < q.tailIndex; i++)
 				describe(s, q.commits[i]);
 		}
 		return s.toString();
 	}
 }