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/*
 * Copyright (c) 2002-2016 "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 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.server.rest.paging;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import org.neo4j.graphdb.Path;
import org.neo4j.graphdb.traversal.Traverser;

public class PagedTraverser implements Iterator>, Iterable>, Leasable
{
    private final int pageSize;
    private final Traverser traverser;
    private Iterator iterator;

    public PagedTraverser( Traverser traverser, int pageSize )
    {
        this.traverser = traverser;
        this.pageSize = pageSize;
    }

    @Override
    public List next()
    {
        ensureIteratorStarted();
        if ( !iterator.hasNext() )
        {
            return null;
        }

        List result = new ArrayList<>();

        for ( int i = 0; i < pageSize; i++ )
        {
            if ( !iterator.hasNext() )
            {
                break;
            }
            result.add( iterator.next() );
        }

        return result;
    }

    private void ensureIteratorStarted()
    {
        if ( iterator == null )
        {
            iterator = traverser.iterator();
        }
    }

    @Override
    public boolean hasNext()
    {
        ensureIteratorStarted();
        return iterator.hasNext();
    }

    @Override
    public void remove()
    {
        iterator.remove();
    }

    @Override
    public Iterator> iterator()
    {
        return this;
    }
}