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eXist-db NoSQL Database n-gram Index
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/*
 * eXist-db Open Source Native XML Database
 * Copyright (C) 2001 The eXist-db Authors
 *
 * [email protected]
 * http://www.exist-db.org
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 */
package org.exist.xquery.modules.ngram.utils;

import org.exist.dom.persistent.ExtArrayNodeSet;
import org.exist.dom.persistent.NodeProxy;
import org.exist.dom.persistent.NodeSet;
import org.exist.dom.persistent.NodeSetIterator;
import org.exist.xquery.XPathException;

import java.util.function.Function;

public final class NodeSets {

    private NodeSets() {
    }

    /**
     * Builds a new NodeSet by applying a function to all NodeProxys of the supplied NodeSet and returning all non-null
     * results.
     * 
     * @param nodes
     *            the NodeSet containig the NodeProys to be transformed
     * @param transform
     *            the function to be applied to all NodeProxys in nodes
     * @return a new NodeSet containing the non-null results of f applied to the NodeProxys in nodes
     *
     * @throws XPathException if an error occurs with the query.
     */
    public static NodeSet transformNodes(final NodeSet nodes, final Function transform) throws XPathException {
        final NodeSet result = new ExtArrayNodeSet();
        for (NodeProxy nodeProxy : nodes) {
            final NodeProxy node = transform.apply(nodeProxy);
            if (node != null) {
                result.add(node);
            }
        }
        result.iterate(); // ensure result is ready to use
        return result;
    }

    public static NodeSet getNodesMatchingAtStart(final NodeSet nodes, final int expressionId) throws XPathException {
        return transformNodes(nodes, proxy ->
                NodeProxies.transformOwnMatches(
                        proxy,
                        match -> match.filterOffsetsStartingAt(0),
                        expressionId
                )
        );
    }

    public static NodeSet getNodesMatchingAtEnd(final NodeSet nodes, final int expressionId) throws XPathException {
        return transformNodes(nodes, proxy ->
                NodeProxies.transformOwnMatches(
                        proxy,
                        match -> match.filterOffsetsEndingAt(proxy.getNodeValue().length()),
                        expressionId
                )
        );
    }

}