public function encodeOutput($data)
    {
        // TODO - use HTTP_ACCEPT here ?
        //var_dump($_SERVER['HTTP_ACCEPT']);

        if ($_GET['format'] == 'xml') {
            throw $this->exception('only JSON format is supported', null, 406);
        }

        if ($_GET['format'] == 'json_pretty') {
            header('Content-type: application/json');
            echo json_encode($data, JSON_PRETTY_PRINT);
            return;
        }

        if ($_GET['format'] == 'html') {
            echo '<pre>';
            echo json_encode($data, JSON_PRETTY_PRINT);
            return;
        }

        header('Content-type: application/json');

        if ($data === null) {
            $data = array();
        }
        echo json_encode($data);
    }