public function backup()
    {
        $count = $this->backups - 1;
        for ($i = $count; $i > 0; --$i) {
            $backupFile = "{$this->filepath}.bkup.{$i}";
            if (file_exists($backupFile)) {
                copy($backupFile, "{$this->filepath}.bkup.".($i + 1));
            }
        }
        copy($this->filepath, "{$this->filepath}.bkup.1");

        return true;
    }