/**
* 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.Iterator;
import java.util.LinkedList;
import java.util.List;
import org.neo4j.graphdb.traversal.TraversalBranch;
import org.neo4j.graphdb.traversal.BranchSelector;
/**
* Selects {@link TraversalBranch}s according to postorder breadth first
* pattern which basically is a reverse to preorder breadth first in that
* deepest levels are returned first, see
* http://en.wikipedia.org/wiki/Breadth-first_search
*/
class PostorderBreadthFirstSelector implements BranchSelector
{
private Iterator<TraversalBranch> sourceIterator;
private TraversalBranch current;
PostorderBreadthFirstSelector( TraversalBranch startSource )
{
this.current = startSource;
}
public TraversalBranch next()
{
if ( sourceIterator == null )
{
sourceIterator = gatherSourceIterator();
}
return sourceIterator.hasNext() ? sourceIterator.next() : null;
}
private Iterator<TraversalBranch> gatherSourceIterator()
{
LinkedList<TraversalBranch> queue = new LinkedList<TraversalBranch>();
queue.add( current.next() );
while ( true )
{
List<TraversalBranch> level = gatherOneLevel( queue );
if ( level.isEmpty() )
{
break;
}
queue.addAll( 0, level );
}
return queue.iterator();
}
private List<TraversalBranch> gatherOneLevel(
List<TraversalBranch> queue )
{
List<TraversalBranch> level = new LinkedList<TraversalBranch>();
Integer depth = null;
for ( TraversalBranch source : queue )
{
if ( depth == null )
{
depth = source.depth();
}
else if ( source.depth() != depth )
{
break;
}
while ( true )
{
TraversalBranch next = source.next();
if ( next == null )
{
break;
}
level.add( next );
}
}
return level;
}
}