content: /*
   * $Header$
   * $Revision$
   * $Date$
   *
   * ====================================================================
   *
   * 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
   * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
   * 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 <bob@werken.com> and 
   * James Strachan <jstrachan@apache.org>.  For more information on the 
   * Jaxen Project, please see <http://www.jaxen.org/>.
   * 
   * $Id$
   */
  
  
  package org.jaxen.function;
  
  import org.jaxen.Context;
  import org.jaxen.Function;
  import org.jaxen.FunctionCallException;
  import org.jaxen.Navigator;
  import org.jaxen.UnsupportedAxisException;
  import org.jaxen.JaxenRuntimeException;
  
  import java.text.DecimalFormat;
  import java.text.NumberFormat;
  import java.text.DecimalFormatSymbols;
  import java.util.List;
  import java.util.Iterator;
  import java.util.Locale;
  
  /**
   * <p>
   * <b>4.2</b> <code><i>string</i> string(<i>object</i>)</code>
   * </p>
   * 
   * 
   * <blockquote src="http://www.w3.org/TR/xpath">
   * <p>
   * The <b>string</b> function converts
   * an object to a string as follows:
   * </p>
   * 
   * <ul>
   * 
   * <li>
   * <p>
   * A node-set is converted to a string by returning the <a
   * href="http://www.w3.org/TR/xpath#dt-string-value" target="_top">string-value</a> of the node in the node-set
   * that is first in <a href="http://www.w3.org/TR/xpath#dt-document-order" target="_top">document order</a>. If
   * the node-set is empty, an empty string is returned.
   * </p>
   * </li>
   * 
   * <li>
   * <p>
   * A number is converted to a string as follows
   * </p>
   * 
   * <ul>
   * 
   * <li>
   * <p>
   * NaN is converted to the string <code>NaN</code>
   * </p>
   * </li>
   * 
   * <li>
   * <p>
   * positive zero is converted to the string <code>0</code>
   * </p>
   * </li>
   * 
   * <li>
   * 
   * <p>
   * negative zero is converted to the string <code>0</code>
   * </p>
   * </li>
   * 
   * <li>
   * <p>
   * positive infinity is converted to the string <code>Infinity</code>
   * </p>
   * </li>
   * 
   * <li>
   * <p>
   * negative infinity is converted to the string <code>-Infinity</code>
   * 
   * </p>
   * </li>
   * 
   * <li>
   * <p>
   * if the number is an integer, the number is represented in decimal
   * form as a <a href="http://www.w3.org/TR/xpath#NT-Number" target="_top">Number</a> with no decimal point and
   * no leading zeros, preceded by a minus sign (<code>-</code>) if
   * the number is negative
   * </p>
   * </li>
   * 
   * <li>
   * <p>
   * otherwise, the number is represented in decimal form as a Number including a decimal point with at least
   * one digit before the decimal point and at least one digit after the
   * decimal point, preceded by a minus sign (<code>-</code>) if the
   * number is negative; there must be no leading zeros before the decimal
   * point apart possibly from the one required digit immediately before
   * the decimal point; beyond the one required digit after the decimal
   * point there must be as many, but only as many, more digits as are
   * needed to uniquely distinguish the number from all other IEEE 754
   * numeric values.
   * </p>
   * 
   * </li>
   * 
   * </ul>
   * 
   * </li>
   * 
   * <li>
   * <p>
   * The boolean false value is converted to the string <code>false</code>.
   * The boolean true value is converted to the string <code>true</code>.
   * </p>
   * </li>
   * 
   * <li>
   * <p>
   * An object of a type other than the four basic types is converted to a
   * string in a way that is dependent on that type.
   * </p>
   * 
   * </li>
   * 
   * </ul>
   * 
   * <p>
   * If the argument is omitted, it defaults to a node-set with the
   * context node as its only member.
   * </p>
   * 
   * </blockquote>
   * 
   * @author bob mcwhirter (bob @ werken.com)
   * @see <a href="http://www.w3.org/TR/xpath#function-string"
   *      target="_top">Section 4.2 of the XPath Specification</a>
   */
  public class StringFunction implements Function
  {
  
      private static DecimalFormat format = (DecimalFormat) NumberFormat.getInstance(Locale.ENGLISH);
      
      static {
          DecimalFormatSymbols symbols = new DecimalFormatSymbols(Locale.ENGLISH);
          symbols.setNaN("NaN");
          symbols.setInfinity("Infinity");
          format.setGroupingUsed(false);
          format.setMaximumFractionDigits(32);
          format.setDecimalFormatSymbols(symbols);
      }
  
      /**
       * Create a new <code>StringFunction</code> object.
       */
      public StringFunction() {}
      
      /**
       * Returns the string-value of <code>args.get(0)</code> 
       * or of the context node if <code>args</code> is empty.
       * 
       * @param context the context at the point in the
       *         expression where the function is called
       * @param args list with zero or one element
       * 
       * @return a <code>String</code> 
       * 
       * @throws FunctionCallException if <code>args</code> has more than one item
       */    
      public Object call(Context context,
                         List args) throws FunctionCallException
      {
          int size = args.size();
  
          if ( size == 0 )
          {
              return evaluate( context.getNodeSet(),
                               context.getNavigator() );
          }
          else if ( size == 1 )
          {
              return evaluate( args.get(0),
                               context.getNavigator() );
          }
  
          throw new FunctionCallException( "string() takes at most argument." );
      }
      
      /**
       * Returns the XPath string-value of <code>obj</code>.
       * This operation is only defined if obj is a node, node-set,
       * <code>String</code>, <code>Number</code>, or 
       * <code>Boolean</code>. For other types this function
       * returns the empty string. 
       * 
       * @param obj the node, node-set, string, number, or boolean
       *      whose string-value is calculated
       * @param nav the navigator used to calculate the string-value
       * 
       * @return a <code>String</code>. May be empty but is never null.
       */    
      public static String evaluate(Object obj,
                                    Navigator nav)
      {
          try
          {
              // Workaround because XOM uses lists for Text nodes
              // so we need to check for that first
              if (nav != null && nav.isText(obj))
              {
                  return nav.getTextStringValue(obj);
              }
              
              if (obj instanceof List)
              {
                  List list = (List) obj;
                  if (list.isEmpty())
                  {
                      return "";
                  }
                  // do not recurse: only first list should unwrap
                  obj = list.get(0);
              }
              
              if (nav != null) {
                  // This stack of instanceof really suggests there's 
                  // a failure to take advantage of polymorphism here
                  if (nav.isElement(obj))
                  {
                      return nav.getElementStringValue(obj);
                  }
                  else if (nav.isAttribute(obj))
                  {
                      return nav.getAttributeStringValue(obj);
                  }
      
                  else if (nav.isDocument(obj))
                  {
                      Iterator childAxisIterator = nav.getChildAxisIterator(obj);
                      while (childAxisIterator.hasNext())
                      {
                          Object descendant = childAxisIterator.next();
                          if (nav.isElement(descendant))
                          {
                              return nav.getElementStringValue(descendant);
                          }
                      }
                  }
                  else if (nav.isProcessingInstruction(obj))
                  {
                      return nav.getProcessingInstructionData(obj);
                  }
                  else if (nav.isComment(obj))
                  {
                      return nav.getCommentStringValue(obj);
                  }
                  else if (nav.isText(obj))
                  {
                      return nav.getTextStringValue(obj);
                  }
                  else if (nav.isNamespace(obj))
                  {
                      return nav.getNamespaceStringValue(obj);
                  }
              }
              
              if (obj instanceof String)
              {
                  return (String) obj;
              }
              else if (obj instanceof Boolean)
              {
                  return stringValue(((Boolean) obj).booleanValue());
              }
              else if (obj instanceof Number)
              {
                  return stringValue(((Number) obj).doubleValue());
              }
              
          }
          catch (UnsupportedAxisException e)
          {
              throw new JaxenRuntimeException(e);
          }
          
          return "";
  
      }
  
      private static String stringValue(double value)
      {
          
          // DecimalFormat formats negative zero as "-0".
          // Therefore we need to test for zero explicitly here.
          if (value == 0) return "0";
          
          // need to synchronize object for thread-safety
          String result = null;
          synchronized (format) {
              result = format.format(value);
          }
          return result;
          
      }
  
      private static String stringValue(boolean value)
      {
          return value ? "true" : "false";
      }
  
  }
  