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;
}
}