/**
* 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.path;
import java.util.Iterator;
import org.neo4j.graphalgo.CostEvaluator;
import org.neo4j.graphalgo.PathFinder;
import org.neo4j.graphalgo.WeightedPath;
import org.neo4j.graphalgo.impl.util.BestFirstSelectorFactory;
import org.neo4j.graphalgo.impl.util.StopAfterWeightIterator;
import org.neo4j.graphdb.Direction;
import org.neo4j.graphdb.Node;
import org.neo4j.graphdb.Path;
import org.neo4j.graphdb.RelationshipExpander;
import org.neo4j.graphdb.traversal.TraversalBranch;
import org.neo4j.graphdb.traversal.TraversalDescription;
import org.neo4j.graphdb.traversal.Traverser;
import org.neo4j.helpers.Predicate;
import org.neo4j.kernel.Traversal;
import org.neo4j.kernel.Uniqueness;
/**
* @author Tobias Ivarsson
* @author Martin Neumann
* @author Mattias Persson
*/
public class Dijkstra implements PathFinder<WeightedPath>
{
private static final TraversalDescription TRAVERSAL =
Traversal.description().uniqueness(
Uniqueness.NONE );
private final RelationshipExpander expander;
private final CostEvaluator<Double> costEvaluator;
public Dijkstra( RelationshipExpander expander, CostEvaluator<Double> costEvaluator )
{
this.expander = expander;
this.costEvaluator = costEvaluator;
}
public Iterable<WeightedPath> findAllPaths( Node start, final Node end )
{
Predicate<Path> filter = new Predicate<Path>()
{
public boolean accept( Path position )
{
return position.endNode().equals( end );
}
};
final Traverser traverser = TRAVERSAL.expand( expander ).order(
new SelectorFactory( costEvaluator ) ).filter( filter ).traverse( start );
return new Iterable<WeightedPath>()
{
public Iterator<WeightedPath> iterator()
{
return new StopAfterWeightIterator( traverser.iterator(),
costEvaluator );
}
};
}
public WeightedPath findSinglePath( Node start, Node end )
{
Iterator<WeightedPath> result = findAllPaths( start, end ).iterator();
return result.hasNext() ? result.next() : null;
}
private static class SelectorFactory extends BestFirstSelectorFactory<Double, Double>
{
private final CostEvaluator<Double> evaluator;
SelectorFactory( CostEvaluator<Double> evaluator )
{
this.evaluator = evaluator;
}
@Override
protected Double calculateValue( TraversalBranch next )
{
return next.depth() == 0 ? 0d : evaluator.getCost(
next.relationship(), Direction.OUTGOING );
}
@Override
protected Double addPriority( TraversalBranch source,
Double currentAggregatedValue, Double value )
{
return withDefault( currentAggregatedValue, 0d ) + withDefault( value, 0d );
}
private <T> T withDefault( T valueOrNull, T valueIfNull )
{
return valueOrNull != null ? valueOrNull : valueIfNull;
}
@Override
protected Double getStartData()
{
return 0d;
}
}
}