protected function watchProgress(OutputInterface $output)
    {
        $progress = new ProgressBar($output);
        $progress->setFormat('%bar% (%percent%%)');
        $this->manager->on('request.start', function ($url, $bytes) use ($progress, $output) {
            $output->writeln('<comment>Downloading ' . basename($url) . '</comment>');
            $progress->start($bytes);
        });
        $this->manager->on('progress', function ($transferred) use ($progress) {
            $progress->setProgress($transferred);
        });
        $this->manager->on('complete', function () use ($progress, $output) {
            $progress->finish();
            $output->writeln('');
        });
    }