protected const ENDPOINT_LISTS     = 'lists';

    /**
     * @var string
     */
    protected $apiKey;

    /**
     * @var string
     */
    protected $dataCenter;

    /**
     * @var HttpClient
     */
    protected $httpClient;

    /**
     * @var string
     */
    protected $password;

    /**
     * @var string
     */
    protected $user;

    public function __construct(string $apiKey, string $dataCenter, string $password, string $user)
    {
        $this->httpClient = HttpClient::create([
            'base_uri' => 'https://' . $dataCenter . '.api.mailchimp.com/3.0/',
            'timeout'  => 5,
            'headers'  => [
                'Authorization' => 'Basic ' . base64_encode($user . ':' . $password),
            ],
        ]);

        $this->apiKey     = $apiKey;
        $this->dataCenter = $dataCenter;
        $this->user       = $user;
        $this->password   = $password;
    }

    public function getLists(): ?array
    {
        $response = $this->httpClient->request(Request::METHOD_GET, self::ENDPOINT_LISTS);

        if ($response instanceof Response && $response->getStatusCode() === HttpFoundationResponse::HTTP_OK) {
            return $this->getContents($response);
        }

        return null;
    }

    protected function getContents(Response $response): ?array
    {
        return json_decode($response->getBody()->getContents(), true, 512, JSON_THROW_ON_ERROR);
    }