/*
    * $Header$
    * $Revision$
    * $Date$
    *
    * ====================================================================
    *
    * 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 java.util.List;
  
  import org.jaxen.Context;
  import org.jaxen.Function;
  import org.jaxen.FunctionCallException;
  import org.jaxen.Navigator;
  
  /**
   * <p>
   * <b>4.3</b> <code><i>boolean</i> boolean(<i>object</i>)</code>
   * </p>
   * 
   * <blockquote cite="http://www.w3.org/TR/xpath#section-Boolean-Functions">
   * <p>
   * The <b><a href="https://www.w3.org/TR/xpath#function-boolean" target="_top">boolean</a></b>
   * function converts its argument to a boolean as follows:
   * </p>
   * 
   * <ul>
   * 
   * <li>
   * <p>
   * a number is true if and only if it is neither positive or negative
   * zero nor NaN
   * </p>
   * </li>
   * 
   * <li>
   * <p>
   * a node-set is true if and only if it is non-empty
   * </p>
   * </li>
   * 
   * <li>
   * <p>
   * a string is true if and only if its length is non-zero
   * </p>
   * </li>
   * 
   * <li>
   * 
   * <p>
   * an object of a type other than the four basic types is converted to a
   * boolean in a way that is dependent on that type
   * </p></li></ul>
   * </blockquote>
   * 
   * @author bob mcwhirter (bob @ werken.com)
   * @see <a href="https://www.w3.org/TR/xpath#function-boolean">Section 4.3 of the XPath Specification</a>
  */
 public class BooleanFunction implements Function
 {
 
 
     /**
      * Create a new <code>BooleanFunction</code> object.
      */
     public BooleanFunction() {}
     
     /** Convert the argument to a <code>Boolean</code>
      *
      * @param context the context at the point in the
      *         expression when the function is called
      * @param args a list with exactly one item which will be converted to a 
      *     <code>Boolean</code>
      * 
      * @return the result of evaluating the function; 
      *     <code>Boolean.TRUE</code> or <code>Boolean.FALSE</code>
      * 
      * @throws FunctionCallException if <code>args</code> has more or less than one item
      */
     public Object call(Context context,
                        List args) throws FunctionCallException
     {
         if ( args.size() == 1 )
         {
             return evaluate( args.get(0), context.getNavigator() );
         }
 
         throw new FunctionCallException("boolean() requires one argument");
     }
 
     /** 
      * <p>Convert the argument <code>obj</code> to a <code>Boolean</code> 
      * according to the following rules:</p>
      *
      * <ul>
      * <li>Lists are false if they're empty; true if they're not.</li>
      * <li>Booleans are false if they're false; true if they're true.</li>
      * <li>Strings are false if they're empty; true if they're not.</li>
      * <li>Numbers are false if they're 0 or NaN; true if they're not.</li>
      * <li>All other objects are true.</li>
      * </ul>
      * 
      * @param obj the object to convert to a boolean
      * @param nav ignored
      * 
      * @return <code>Boolean.TRUE</code> or <code>Boolean.FALSE</code>
      */
     public static Boolean evaluate(Object obj, Navigator nav)
     {
         if ( obj instanceof List )
         {
             List list = (List) obj;
             
             // if it's an empty list, then we have a null node-set -> false            
             if (list.size() == 0)
             {
                 return Boolean.FALSE;
             }
      
             // otherwise, unwrap the list and check the primitive
             obj = list.get(0);
         }
         
         // now check for primitive types
         // otherwise a non-empty node-set is true
 
         // if it's a Boolean, let it decide
         if ( obj instanceof Boolean )
         {
             return (Boolean) obj;
         }
         // if it's a Number, != 0 -> true
         else if ( obj instanceof Number )
         {
             double d = ((Number) obj).doubleValue();
             if ( d == 0 || Double.isNaN(d) )
             {
                 return Boolean.FALSE;
             }
             return Boolean.TRUE;
         }
         // if it's a String, "" -> false
         else if ( obj instanceof String )
         {
             return ( ((String)obj).length() > 0
                      ? Boolean.TRUE
                      : Boolean.FALSE );
         }
         else 
         {
             // assume it's a node so that this node-set is non-empty 
             // and so it's true
             return ( obj != null ) ? Boolean.TRUE : Boolean.FALSE;
         }
 
     }
 }