/*
 * 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 <http://www.gnu.org/licenses/>.
 */
package org.neo4j.graphalgo;

import org.neo4j.annotations.api.PublicApi;
import org.neo4j.graphdb.Direction;
import org.neo4j.graphdb.Relationship;

/**
 * In order to make the solving of shortest path problems as general as
 * possible, the algorithms accept objects handling all relevant tasks regarding
 * costs of paths. This allows the user to represent the costs in any possible
 * way, and to calculate them in any way. The usual case is numbers that we just
 * add together, but what if we have for example factors we would like to
 * multiply instead? This is handled by this system, which works as follows. A
 * CostEvaluator is used to get the cost for a single relationship. These costs
 * are then added through a CostAccumulator. Costs for alternative paths are
 * compared with a common java.util.Comparator.
 *
 * @param <T> The data type the edge weights are represented by.
 */
@PublicApi
public interface CostEvaluator<T> {
    /**
     * This is the general method for looking up costs for relationships. This
     * can do anything, like looking up a property or running some small
     * calculation.
     *
     * @param relationship the relationship to get the cost for
     * @param direction The direction in which the relationship is being
     *            evaluated, either {@link Direction#INCOMING} or
     *            {@link Direction#OUTGOING}.
     * @return The cost for this edge/relationship
     */
    T getCost(Relationship relationship, Direction direction);
}
