class LanguageBlock

class LanguageBlock extends BlockBase implements ContainerFactoryPluginInterface {
    
    /**
     * The language manager.
     *
     * @var \Drupal\Core\Language\LanguageManagerInterface
     */
    protected $languageManager;
    
    /**
     * The path matcher.
     *
     * @var \Drupal\Core\Path\PathMatcherInterface
     */
    protected $pathMatcher;
    
    /**
     * Constructs a LanguageBlock object.
     *
     * @param array $configuration
     *   A configuration array containing information about the plugin instance.
     * @param string $plugin_id
     *   The plugin ID for the plugin instance.
     * @param mixed $plugin_definition
     *   The plugin implementation definition.
     * @param \Drupal\Core\Language\LanguageManagerInterface $language_manager
     *   The language manager.
     * @param \Drupal\Core\Path\PathMatcherInterface $path_matcher
     *   The path matcher.
     */
    public function __construct(array $configuration, $plugin_id, $plugin_definition, LanguageManagerInterface $language_manager, PathMatcherInterface $path_matcher) {
        parent::__construct($configuration, $plugin_id, $plugin_definition);
        $this->languageManager = $language_manager;
        $this->pathMatcher = $path_matcher;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
        return new static($configuration, $plugin_id, $plugin_definition, $container->get('language_manager'), $container->get('path.matcher'));
    }
    
    /**
     * {@inheritdoc}
     */
    protected function blockAccess(AccountInterface $account) {
        $access = $this->languageManager
            ->isMultilingual() ? AccessResult::allowed() : AccessResult::forbidden();
        return $access->addCacheTags([
            'config:configurable_language_list',
        ]);
    }
    
    /**
     * {@inheritdoc}
     */
    public function build() {
        $build = [];
        $type = $this->getDerivativeId();
        $route_match = \Drupal::routeMatch();
        // If there is no route match, for example when creating blocks on 404 pages
        // for logged-in users with big_pipe enabled using the front page instead.
        if ($this->pathMatcher
            ->isFrontPage() || !$route_match->getRouteObject()) {
            // We are skipping the route match on both 404 and front page.
            // Example: If on front page, there is no route match like when creating
            // blocks on 404 pages for logged-in users with big_pipe enabled, use the
            // front page.
            $url = Url::fromRoute('<front>');
        }
        else {
            $url = Url::fromRouteMatch($route_match);
        }
        $links = $this->languageManager
            ->getLanguageSwitchLinks($type, $url);
        if (isset($links->links)) {
            $build = [
                '#theme' => 'links__language_block',
                '#links' => $links->links,
                '#attributes' => [
                    'class' => [
                        "language-switcher-{$links->method_id}",
                    ],
                ],
                '#set_active_class' => TRUE,
            ];
        }
        return $build;
    }
    
    /**
     * {@inheritdoc}
     *
     * @todo Make cacheable in https://www.drupal.org/node/2232375.
     */
    public function getCacheMaxAge() {
        return 0;
    }

}