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Collections and collection utilities for Neo4j.

There is a newer version: 5.24.0

/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [https://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.internal.helpers.collection;

import java.util.Iterator;
import org.neo4j.graphdb.ResourceIterator;

public abstract class NestingResourceIterator extends PrefetchingResourceIterator {
    private final Iterator source;
    private ResourceIterator currentNestedIterator;

    protected NestingResourceIterator(Iterator source) {
        this.source = source;
    }

    protected abstract ResourceIterator createNestedIterator(U item);

    @Override
    protected T fetchNextOrNull() {
        if (currentNestedIterator == null || !currentNestedIterator.hasNext()) {
            while (source.hasNext()) {
                U currentSurfaceItem = source.next();
                close();
                currentNestedIterator = createNestedIterator(currentSurfaceItem);
                if (currentNestedIterator.hasNext()) {
                    break;
                }
            }
        }
        return currentNestedIterator != null && currentNestedIterator.hasNext() ? currentNestedIterator.next() : null;
    }

    @Override
    public void close() {
        if (currentNestedIterator != null) {
            currentNestedIterator.close();
        }
    }
}