public function listCommand()
    {
        $this->output->outputLine();
        $this->output->outputLine('<b>Available Backups</b>');
        $this->output->outputLine();
        $this->output->outputLine('<b>Identifier  Date       Time</b>');

        $this->initialize();
        $availableVersions = $this->backupService->getAvailableVersions();

        foreach ($availableVersions as $version) {
            if ( is_numeric($version) ) {
                $this->output->outputLine($version . ': ' . date('d.m.Y H:i', $version * 1));
            }
        }
        $this->output->outputLine();
    }