/**
* 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.EstimateEvaluator;
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;
public class ExperimentalAStar implements PathFinder<WeightedPath>
{
private final TraversalDescription traversalDescription;
private final CostEvaluator<Double> costEvaluator;
private final EstimateEvaluator<Double> estimateEvaluator;
public ExperimentalAStar( RelationshipExpander expander, CostEvaluator<Double> costEvaluator,
EstimateEvaluator<Double> estimateEvaluator )
{
this.traversalDescription = Traversal.description().uniqueness(
Uniqueness.NONE ).expand( expander );
this.costEvaluator = costEvaluator;
this.estimateEvaluator = estimateEvaluator;
}
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 = traversalDescription.order(
new SelectorFactory( end ) ).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> paths = findAllPaths( start, end ).iterator();
return paths.hasNext() ? paths.next() : null;
}
private static class PositionData implements Comparable<PositionData>
{
private final double wayLengthG;
private final double estimateH;
public PositionData( double wayLengthG, double estimateH )
{
this.wayLengthG = wayLengthG;
this.estimateH = estimateH;
}
Double f()
{
return this.estimateH + this.wayLengthG;
}
public int compareTo( PositionData o )
{
return f().compareTo( o.f() );
}
@Override
public String toString()
{
return "g:" + wayLengthG + ", h:" + estimateH;
}
}
private class SelectorFactory extends BestFirstSelectorFactory<PositionData, Double>
{
private final Node end;
SelectorFactory( Node end )
{
this.end = end;
}
@Override
protected PositionData addPriority( TraversalBranch source,
PositionData currentAggregatedValue, Double value )
{
return new PositionData( currentAggregatedValue.wayLengthG + value,
estimateEvaluator.getCost( source.node(), end ) );
}
@Override
protected Double calculateValue( TraversalBranch next )
{
return next.depth() == 0 ? 0d :
costEvaluator.getCost( next.relationship(), Direction.OUTGOING );
}
@Override
protected PositionData getStartData()
{
return new PositionData( 0, 0 );
}
}
}