Atualizar o plug-in de pesquisa do Joomla 2.5 para o Joomla 3.x

Eu tenho um plug-in de pesquisa, desenvolvido para o Joomla 2.5, o código no search.php é o seguinte:

    <?php

    //To prevent accessing the document directly, enter this code:
    // no direct access

    defined( '_JEXEC' ) or die( 'Restricted access' );

    $mainframe->registerEvent( 'onSearch', 'plgSearchHotels' );

    JPlugin::loadLanguage( 'plg_search_hotels' );

    function &plgSearchHotelsAreas()
    {
            static $areas = array(
                    'hotels' => 'Hotels'
            );
            return $areas;
    } 

    function plgSearchHotels ( $searchdate, $airport, $resort, $numadults, $numchild, $numinfants, $ordering='' )
    {
            $db    =& JFactory::getDBO();
            $user  =& JFactory::getUser(); 

            $plugin =& JPluginHelper::getPlugin('search', 'hotels');

            $searchdate = trim( $searchdate );
            $numpassengers = $numadults + $numchild;

            if ($searchdate == '') {
                return array();
            }


            switch ( $ordering ) {
    //alphabetic, ascending
                    case 'alpha':
                            $order = 'a.name ASC';
                            break;
    //oldest first
                    case 'oldest':
    //popular first
                    case 'popular':
    //newest first
                    case 'newest':
    //default setting: alphabetic, ascending
                    default:
                            $order = 'a.name ASC';
            }

            $searchHotels = JText::_( 'Hotels' );

            $query = 'SELECT mykey, hotelName, resortName, dep, startDate, sellingPrice FROM Availability WHERE startDate = "'.$searchdate.'" AND available = "Y"';
            if($airport !== "A") $query .= ' AND dep = "'.$airport.'"';
            if($resort !== "A") $query .= ' AND resortCode = "'.$resort.'"';
            $query .= ' AND seats >= '.$numpassengers;
            $query .= ' AND beds >= '.$numpassengers.' ORDER BY sellingPrice ASC';

            $db->setQuery( $query, 0, $limit );
            $rows = $db->loadObjectList();

            return $rows;
    }
    ?>

No entanto, quando tento usar esse código no Joomla 3.3, ele não está funcionando corretamente. Alguma idéia do que estou fazendo de errado?