/**
 * Quick example of adding a custom filter
 * A simple copy and paste of the existing Category filter
 * Refer to the last line for how it adds itself to the interface
 * Find this new filter in: WP Admin > Events > Settings > Filterbar
 * Docs for TribeEventsFilter: http://docs.tri.be/Filter-Bar/class-TribeEventsFilter.html
 */
class TribeEventsFilter_Custom extends TribeEventsFilter {
    public $type = 'checkbox';

    protected function get_values() {
        /** @var wpdb $wpdb */
        global $wpdb;

        // get venue IDs associated with published posts
        $cities = $wpdb->get_col($wpdb->prepare("SELECT DISTINCT m.meta_value FROM {$wpdb->postmeta} m  WHERE m.meta_key='_VenueCity'", TribeEvents::POSTTYPE));
        $cities = array_filter($cities);


        if ( empty($cities) ) {
            return array();
        }
        $cities_array = array();
        foreach( $cities as $city ) {
            if($city != ''){
                $cities_array[] = array(
                    'name' => $city,
                    'value' => $city,
                );
            }
        }

        function querySort ($x, $y) {
            return strcasecmp($x['name'], $y['name']);
        }

        usort($cities_array, 'querySort');

        return $cities_array;
    }

    protected function setup_query_args() {
        /*$this->queryArgs = array( 'meta_query' => array( array(
            'key' => '_VenueCity',
            'value' => 'Rotterdam',
        ) ) );*/
    }

}



// This adds our new filter to the Filterbar options
// Invokes TribeEventsFilter::__construct($name, $slug);
$taxonomy_example = new TribeEventsFilter_Custom('Plaats', 'city');