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/*
 * Copyright (c) 2011 Salzburg Research.
 *
 * 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 at.newmedialab.ldpath.model.functions;

import at.newmedialab.ldpath.api.backend.RDFBackend;
import at.newmedialab.ldpath.api.functions.SelectorFunction;

import java.util.Collection;
import java.util.Collections;

/**
 * Selects the first node in the argument list.
 * 
 * @author jakob
 * 
 */
public class FirstFunction implements SelectorFunction {


    /**
     * Apply the function to the list of nodes passed as arguments and return the result as type T.
     * Throws IllegalArgumentException if the function cannot be applied to the nodes passed as argument
     * or the number of arguments is not correct.
     *
     * @param args a nested list of KiWiNodes
     * @return
     */
    @Override
    public Collection apply(RDFBackend rdfBackend, Node context, Collection... args) throws IllegalArgumentException {
        for (Collection arg : args) {
            if (arg.size() > 0) { return arg; }
        }
        return Collections.emptyList();
    }

    /**
     * Return the name of the NodeFunction for registration in the function registry
     *
     * @return
     * @param backend
     */
    @Override
    public String getPathExpression(RDFBackend backend) {
        return "first";
    }
}