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Graph Database API for Neo4j.
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/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [http://neo4j.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 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
package org.neo4j.graphdb.impl.traversal;

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import java.util.function.Predicate;

import org.neo4j.function.Predicates;
import org.neo4j.graphdb.Direction;
import org.neo4j.graphdb.Node;
import org.neo4j.graphdb.Path;
import org.neo4j.graphdb.traversal.BranchCollisionDetector;
import org.neo4j.graphdb.traversal.Evaluation;
import org.neo4j.graphdb.traversal.Evaluator;
import org.neo4j.graphdb.traversal.TraversalBranch;

public class StandardBranchCollisionDetector implements BranchCollisionDetector
{
    private final Map[]> paths = new HashMap<>( 1000 );
    private final Evaluator evaluator;
    private final Set returnedPaths = new HashSet<>();
    private Predicate pathPredicate = Predicates.alwaysTrue();

    @Deprecated
    public StandardBranchCollisionDetector( Evaluator evaluator )
    {
        this.evaluator = evaluator;
    }

    public StandardBranchCollisionDetector( Evaluator evaluator, Predicate pathPredicate )
    {
        this.evaluator = evaluator;
        if ( pathPredicate != null )
        {
            this.pathPredicate = pathPredicate;
        }
    }

    @Override
    @SuppressWarnings( "unchecked" )
    public Collection evaluate( TraversalBranch branch, Direction direction )
    {
        // [0] for paths from start, [1] for paths from end
        Collection[] pathsHere = paths.get( branch.endNode() );
        int index = direction.ordinal();
        if ( pathsHere == null )
        {
            pathsHere = new Collection[] {new ArrayList<>(), new ArrayList<>() };
            paths.put( branch.endNode(), pathsHere );
        }
        pathsHere[index].add( branch );

        // If there are paths from the other side then include all the
        // combined paths
        Collection otherCollections = pathsHere[index == 0 ? 1 : 0];
        if ( !otherCollections.isEmpty() )
        {
            Collection foundPaths = new ArrayList<>();
            for ( TraversalBranch otherBranch : otherCollections )
            {
                TraversalBranch startPath = index == 0 ? branch : otherBranch;
                TraversalBranch endPath = index == 0 ? otherBranch : branch;
                BidirectionalTraversalBranchPath path = new BidirectionalTraversalBranchPath(
                        startPath, endPath );
                if ( isAcceptablePath( path ) )
                {
                    if ( returnedPaths.add( path ) && includePath( path, startPath, endPath ) )
                    {
                        foundPaths.add( path );
                    }
                }
            }

            if ( !foundPaths.isEmpty() )
            {
                return foundPaths;
            }
        }
        return null;
    }

    private boolean isAcceptablePath( BidirectionalTraversalBranchPath path )
    {
        return pathPredicate.test( path );
    }

    protected boolean includePath( Path path, TraversalBranch startPath, TraversalBranch endPath )
    {
        Evaluation eval = evaluator.evaluate( path );
        if ( !eval.continues() )
        {
            startPath.evaluation( eval );
            endPath.evaluation( eval );
        }
        return eval.includes();
    }
}