/**
* Copyright (c) 2002-2011 "Neo Technology,"
* Network Engine for Objects in Lund AB [http://neotechnology.com]
*
* This file is part of Neo4j.
*
* Neo4j is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package org.neo4j.kernel;
import java.util.LinkedList;
import java.util.Queue;
import org.neo4j.graphdb.traversal.TraversalBranch;
import org.neo4j.graphdb.traversal.BranchSelector;
/**
* Selects {@link TraversalBranch}s according to breadth first
* pattern, the most natural ordering in a breadth first search, see
* http://en.wikipedia.org/wiki/Breadth-first_search
*/
class PreorderBreadthFirstSelector implements BranchSelector
{
private final Queue<TraversalBranch> queue = new LinkedList<TraversalBranch>();
private TraversalBranch current;
PreorderBreadthFirstSelector( TraversalBranch startSource )
{
this.current = startSource;
}
public TraversalBranch next()
{
TraversalBranch result = null;
while ( result == null )
{
TraversalBranch next = current.next();
if ( next != null )
{
queue.add( next );
result = next;
}
else
{
current = queue.poll();
if ( current == null )
{
return null;
}
}
}
return result;
}
}