protected function getFileParts($filename)
    {
        if (preg_match('/(.*)@(\d+)x\.(.*)$/', $filename, $matches)) {
            $name = $matches[1];
            $extension = $matches[3];
            $extra = (int) $matches[2];
            $type = 'alternative';

            if ($extra === 1) {
                $type = 'base';
                $extra = null;
            }
        } else {
            $fileParts = explode('.', $filename);

            $name = array_shift($fileParts);
            $extension = null;
            $extra = null;
            $type = 'base';

            while (($part = array_shift($fileParts)) !== null) {
                if ($part !== 'meta' && $part !== 'thumb') {
                    if (null !== $extension) {
                        $name .= '.' . $extension;
                    }
                    $extension = $part;
                } else {
                    $type = $part;
                    $extra = '.' . $part . '.' . implode('.', $fileParts);
                    break;
                }
            }
        }

        return array($name, $extension, $type, $extra);
    }