uk.gov.gchq.gaffer.data.graph.adjacency.PrunedAdjacencyMaps Maven / Gradle / Ivy

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/*
 * Copyright 2017-2020 Crown Copyright
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package uk.gov.gchq.gaffer.data.graph.adjacency;

import java.util.ArrayList;
import java.util.List;
import java.util.Set;

/**
 * A {@code PrunedAdjacencyMaps} object represents a collection of {@link
 * AdjacencyMap}s containing graph adjacency information.
 * 
 * As the {@link AdjacencyMap}s are added, a comparison is made between the
 * destination vertices of the previous map and the source vertices of the newly
 * added map. Any entries in the preceding map which do not join up with a
 * source vertex in the new map are deemed to be orphaned paths, and are
 * removed.
 */
public class PrunedAdjacencyMaps implements AdjacencyMaps {

    /**
     * The backing list.
     */
    private final List adjacencyMaps = new ArrayList<>();

    @Override
    public void add(final AdjacencyMap adjacencyMap) {
        removeOrphans(adjacencyMaps, adjacencyMap);
        adjacencyMaps.add(adjacencyMap);
    }

    /**
     * Remove orphaned edges from the AdjacencyMap.
     * 

     * An orphaned edge is one which does not form part of a walk which reaches
     * a destination vertex in the "topmost" adjacency map under consideration.
     * 

     * This method will recursively process all maps in the provided adjacency
     * map list.
     *
     * @param maps the list of adjacency maps being considered
     * @param curr the "topmost" adjacency map under consideration
     */
    private void removeOrphans(final List maps, final AdjacencyMap curr) {
        if (!maps.isEmpty()) {
            final AdjacencyMap prev = maps.get(maps.size() - 1);

            final Set