/**
* 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.graphalgo.impl.util;
import java.util.HashSet;
import java.util.Set;
import org.neo4j.graphalgo.impl.util.PriorityMap.Converter;
import org.neo4j.graphalgo.impl.util.PriorityMap.Entry;
import org.neo4j.graphdb.Node;
import org.neo4j.graphdb.traversal.TraversalBranch;
import org.neo4j.graphdb.traversal.BranchSelector;
import org.neo4j.graphdb.traversal.BranchOrderingPolicy;
public abstract class BestFirstSelectorFactory<P extends Comparable<P>, D>
implements BranchOrderingPolicy
{
public BranchSelector create( TraversalBranch startSource )
{
return new BestFirstSelector( startSource, getStartData() );
}
protected abstract P getStartData();
public final class BestFirstSelector implements BranchSelector
{
private PriorityMap<TraversalBranch, Node, P> queue =
PriorityMap.withNaturalOrder( CONVERTER );
private TraversalBranch current;
private P currentAggregatedValue;
private final Set<Long> visitedNodes = new HashSet<Long>();
public BestFirstSelector( TraversalBranch source, P startData )
{
this.current = source;
this.currentAggregatedValue = startData;
}
public TraversalBranch next()
{
// Exhaust current if not already exhausted
while ( true )
{
TraversalBranch next = current.next();
if ( next != null )
{
if ( !visitedNodes.contains( next.node().getId() ) )
{
P newPriority = addPriority( next, currentAggregatedValue,
calculateValue( next ) );
queue.put( next, newPriority );
}
}
else
{
break;
}
}
// Pop the top from priorityMap
Entry<TraversalBranch, P> entry = queue.pop();
if ( entry != null )
{
current = entry.getEntity();
currentAggregatedValue = entry.getPriority();
visitedNodes.add( current.node().getId() );
return current;
}
return null;
}
}
protected abstract P addPriority( TraversalBranch source,
P currentAggregatedValue, D value );
protected abstract D calculateValue( TraversalBranch next );
public static final Converter<Node, TraversalBranch> CONVERTER =
new Converter<Node, TraversalBranch>()
{
public Node convert( TraversalBranch source )
{
return source.node();
}
};
}