(function() 
{   
    /**
     * Fills a combo box with values from an XML file, further specified
     * by using the query
     */
    jQuery.fn.fillFromXML = function(xmlDocument, query) 
    {  	
        var elementToUpdate = $(this);
        
	$(this).empty();
        $(elementToUpdate).append('<option value="Please Select">Please Select</option>');
	$(xmlDocument).find(query).each(function()
	{		
            if ( $(elementToUpdate).find("option:contains('" + $(this).text() + "')").length == 0 )
            {
                $(elementToUpdate).append('<option value="' + $(this).text() + '">' + $(this).text() + '</option>');
            }
	});	
    }
	
    /**
     * Appends an option to an existing combo box
     */
    jQuery.fn.appendOption = function(value, label, empty)
    {				
	if (empty) $(this).empty();
	
	if ( $(this).find(" option[@value='" + value + "']").length == 0 )
	{
		$(this).append('<option value="' + value + '">' + label + '</option>');
	}
    }

    /**
     * Loads an XML file into memory and returns it 
     * as a jQuery object
     */
    jQuery.load = function(xmlURL)
    {
        var xmlDocument;
		
        $.ajax({type:"GET", async:false, url:xmlURL, dataType:"xml", success: function(xml)
        {
            xmlDocument = xml;
	}});

	return xmlDocument;
    }
	
    /**
     * Sorts a collection of XML elements into a specific order
     * denoted by the query
     */
    jQuery.fn.sort = function(query)
    {
        var list = jQuery.makeArray(this);

        list = jQuery.makeArray(this).sort(function(a,b)
        {		
            if ( Number($(a).attr(query)) < Number($(b).attr(query)) ) return -1;
            else if ( Number($(a).attr(query)) > Number($(b).attr(query)) ) return 1;
            else return 0;
        });

        return list;
    }
	

    /**
     * Determines whether two entities are equal to each other
     */    
    jQuery.fn.equals = function(other)
    {
        var value = $(this).text();

        if ( value != other )
        {
            return false;
        }    

        return true;
    }
	
    /**
     * Returns the count of how many times a value
     * is repeated in the specified array
     */    
    jQuery.howManyInArray = function(value, arr)
    {
        var count = 0;

        $(arr).each(function()
        {
           if (this == value) count++;
        });

        return count;
    }
       
    /**
     * Returns an array of parameter values inside the URL
     * string of the current browser page with parameter name
     * of 'param'
     */
    jQuery.getHttpGetParameters = function(param)
    {
        // split the URL at the ? character
        var hrefArray = document.location.href.split('?');

        // if the split produces only 1 array element then return an error
        if (hrefArray.length == 1)
        {
            alert('No parameters detected.');
            return '';
        }

        // split the 2nd part of the array at the & character
        var parameterPairs = hrefArray[1].split('&');
        var parameterValues = '';

        // iterate over the pairings (param1=a,param2=b)
        for (var pair in parameterPairs)
        {
            // get the param and value into array
            var bits = parameterPairs[pair].split('=');

            // if the param equals our chosen param, then add it to the list
            if (bits[0] == param)
            {
                parameterValues += bits[1] + ',';
            }
        }  

        return parameterValues.substring(0, parameterValues.length-1).split(',');
    }    
    
    /**
     * finds all images specified by the query and if they
     * don't physically exist then replace them with another
     * image
     */
    jQuery.fn.checkImages = function(replacement)
    {
        $(this).each(function()
        {
            if ( !$.isImageOK(this) )
            {
                 if (replacement == null)
                 {
                     $(this).hide();
                 }
                 else
                 {
                     $(this).attr('src', replacement);
                 }
            }
        });    
    }

    /**
     * Checks an image to see if it exists
     */
    jQuery.isImageOK = function(img)
    {   
        // During the onload event, IE correctly identifies any images that
        // weren't downloaded as not complete. Others should too. Gecko-based
        // browsers act like NS4 in that they report this incorrectly.
        if (!img.complete) 
        {
            return false;
        }

        // However, they do have two very useful properties: naturalWidth and
        // naturalHeight. These give the true size of the image. If it failed
        // to load, either of these should be zero.
        if (typeof img.naturalWidth != "undefined" && img.naturalWidth == 0) 
        {
            return false;
        }

        // No other way of checking: assume it's ok.
        return true;
    }   

    /**
     * Renders a dropdown combo box on screen, with a label and
     * default option of 'Please Select'
     */
    jQuery.fn.renderDropdown = function (label, id, onchange)
    {
        $(this).append('<div class="childCombo comboWrapper">' +
            '<label for="' + id + '">' + label + '</label>' +
            '<select id="' + id + '" onChange="' + onchange + '();"></select>' +
            '</div><br class="clear"/>');

        $('.childCombo').show();

        $("#" + id).appendOption('Please Select', 'Please Select', false);
    }

})(jQuery);