public function process_shortcode($args = array(), $content = '')
    {
        global $appointments;
        $args = wp_parse_args($args, $this->_defaults_to_args());
        $services = $appointments->get_services($args['order_by']);
        $model = App_Locations_Model::get_instance();
        $locations = array();
        foreach ($services as $srv) {
            if (empty($srv->ID)) {
                continue;
            }
            $location_id = App_Locations_ServiceLocations::service_to_location_id($srv->ID);
            if (!empty($location_id)) {
                $locations[$location_id] = $model->find_by('id', $location_id);
            }
        }
        $locations = array_values(array_filter($locations));
        if (empty($locations)) {
            return $content;
        }
        $ret = '';
        $ret .= '<div class="app_service_locations">';
        $ret .= '<div class="app_service_locations_dropdown">';
        $ret .= '<div class="app_service_locations_dropdown_title">';
        $ret .= $args['select'];
        $ret .= '</div>';
        $ret .= '<div class="app_service_locations_dropdown_select">';
        $ret .= '<select name="app_service_location">';
        foreach ($locations as $location) {
            /** @var App_Locations_DefaultLocation $location */
            $ret .= '<option value="' . esc_attr($location->get_id()) . '" ' . selected($this->_requested_location_id, $location->get_id(), false) . '>' . esc_html($location->get_display_markup(false)) . '</option>';
        }
        $ret .= '</select>';
        if (empty($args['autorefresh'])) {
            $ret .= '<input type="button" class="app_service_locations_button" value="' . esc_attr($args['show']) . '">';
        }
        $ret .= '</div>';
        $ret .= '</div>';
        $href = add_query_arg('app_service_location', '::asl::', remove_query_arg(array('app_provider_location', 'app_provider_id')));
        $script = <<<EO_SELECTION_JAVASCRIPT
function app_service_locations_redirect () {
\tvar selected = \$(".app_service_locations_dropdown_select select").first().val();
\twindow.location = '{$href}'.replace(/::asl::/, selected);
}
\$(".app_service_locations_button").click(app_service_locations_redirect);
EO_SELECTION_JAVASCRIPT;
        if (!empty($args['autorefresh'])) {
            $script .= '$(".app_service_locations_dropdown_select select").change(app_service_locations_redirect);';
        }
        $appointments->add2footer($script);
        return $ret;
    }
 public static function serve()
 {
     $me = new App_Locations_ServiceLocations();
     $me->_add_hooks();
 }