public static function size($file = false, $format = 'bytes') {

        if ($file && self::isFile($file)) {

            $size = filesize($file);

            switch ($format) {
                case 'bytes':
                    return $size;
                    break;
                case 'kb':
                    return Number::round(($size / 1024), 2);
                    break;
                case 'mb':
                    return Number::round(($size / 1048576), 2);
                    break;
            }
        }

        return false;
    }