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/*
 * $Header$
 * $Revision$
 * $Date$
 *
 * ====================================================================
 *
 * Copyright 2000-2002 bob mcwhirter & James Strachan.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 * 
 *   * Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 * 
 *   * Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 * 
 *   * Neither the name of the Jaxen Project nor the names of its
 *     contributors may be used to endorse or promote products derived 
 *     from this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
 * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
 * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * ====================================================================
 * This software consists of voluntary contributions made by many 
 * individuals on behalf of the Jaxen Project and was originally 
 * created by bob mcwhirter  and 
 * James Strachan .  For more information on the 
 * Jaxen Project, please see .
 * 
 * $Id$
 */

package org.jaxen.function;

import java.util.List;

import org.jaxen.Context;
import org.jaxen.Function; 

/**
 *  4.1 number count(node-set) 
 *  
 * 
 * The count function returns the number of nodes in the argument node-set.
 * 
 * @author bob mcwhirter (bob @ werken.com)
 * @see Section 4.1 of the XPath Specification
 */
@SuppressWarnings({"rawtypes"})
public class CountFunction implements Function
{

    /**
     * Create a new CountFunction object.
     */
    public CountFunction() {}
    
    /**
     * 
     * Returns the number of nodes in the specified node-set.
     * 
     * @param context ignored
     * @param args the function arguments
     * 
     * @return a Double giving the integral number of items in the first argument
     * 
     * @ if args does not have exactly one 
     *     item; or that item is not a List
     */
    public Object call(Context context,
                       List args) 
    {
        if (args.size() == 1)
        {
            return evaluate( args.get(0) );
        }

        throw new RuntimeException( "count() requires one argument." );
    }

    /**
     * 
     * Returns the number of nodes in the specified node-set.
     * 
     * 
     * @param obj a List of nodes
     * @return the integral number of items in the list
     * @ if obj is not a List
     */
    public static Double evaluate(Object obj) 
    {
      
        if (obj instanceof List)
        {
            return Double.valueOf( ((List) obj).size() );
        }
      
        throw new RuntimeException("count() function can only be used for node-sets");
        
    }
    
}