protected function update($currency)
    {
        if (($data = $this->getCurrency($currency)) === null) {
            return $this->error("Currency \"{$currency}\" not found");
        }

        $this->output->write("Updating {$currency} currency...");

        if (is_string($result = $this->storage->update($currency, $data))) {
            $this->output->writeln('<error>' . ($result ?: 'Failed') . '</error>');
        }
        else {
            $this->output->writeln("<info>success</info>");
        }
    }