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/*
 * $Id: InsertBefore.java,v 1.4 2007/11/25 14:18:00 obecker Exp $
 * 
 * The contents of this file are subject to the Mozilla Public License 
 * Version 1.1 (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.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the 
 * License.
 *
 * The Original Code is: this file
 *
 * The Initial Developer of the Original Code is Oliver Becker.
 *
 * Portions created by  ______________________ 
 * are Copyright (C) ______ _______________________. 
 * All Rights Reserved.
 *
 * Contributor(s): ______________________________________. 
 */

package net.sf.joost.stx.function;

import net.sf.joost.grammar.EvalException;
import net.sf.joost.grammar.Tree;
import net.sf.joost.stx.Context;
import net.sf.joost.stx.Value;
import net.sf.joost.stx.function.FunctionFactory.Instance;

import org.xml.sax.SAXException;

/**
 * The insert-before function.

 * Inserts an item or sequence of items into a specified position of a sequence.
 * 
 * @see 
 *      fn:insert-before in "XQuery 1.0 and XPath 2.0 Functions and Operators"
 * @version $Revision: 1.4 $ $Date: 2007/11/25 14:18:00 $
 * @author Oliver Becker
 */
final public class InsertBefore implements Instance
{
   /** @return 3 */
   public int getMinParCount() { return 3; }

   /** @return 3 */
   public int getMaxParCount() { return 3; }

   /** @return "insert-before" */
   public String getName() { return FunctionFactory.FNSP + "insert-before"; }

   /** @return true */
   public boolean isConstant() { return true; }

   public Value evaluate(Context context, int top, Tree args)
      throws SAXException, EvalException
   {
      Value target = args.left.left.evaluate(context, top);
      Value arg2 = args.left.right.evaluate(context, top);
      Value inserts = args.right.evaluate(context, top);

      // make sure that the second parameter is a valid number
      double dPos = arg2.getNumberValue();
      if (Double.isNaN(dPos))
         throw new EvalException("Parameter '" + 
                                 arg2.getStringValue() + 
                                 "' is not a valid index for function '" + 
                                 getName().substring(FunctionFactory.FNSP.length()) + "'");
      long position = Math.round(dPos);

      if (inserts.type == Value.EMPTY)
         return target;
      if (target.type == Value.EMPTY)
         return inserts;

      Value result;
      if (position <= 1)
         // insert before the first item of target
         result = inserts;
      else {
         result = target;
         // determine position
         while (target.next != null && --position > 1)
            target = target.next;
         Value rest = target.next;
         target.next = inserts;
         target = rest;
      }
      // append rest of target 
      while (inserts.next != null)
         inserts = inserts.next;
      inserts.next = target;

      return result;
   }
}