class SystemBrandingBlock

class SystemBrandingBlock extends BlockBase implements ContainerFactoryPluginInterface {
    
    /**
     * Stores the configuration factory.
     *
     * @var \Drupal\Core\Config\ConfigFactoryInterface
     */
    protected $configFactory;
    
    /**
     * Creates a SystemBrandingBlock instance.
     *
     * @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\Config\ConfigFactoryInterface $config_factory
     *   The factory for configuration objects.
     */
    public function __construct(array $configuration, $plugin_id, $plugin_definition, ConfigFactoryInterface $config_factory) {
        parent::__construct($configuration, $plugin_id, $plugin_definition);
        $this->configFactory = $config_factory;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
        return new static($configuration, $plugin_id, $plugin_definition, $container->get('config.factory'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function defaultConfiguration() {
        return [
            'use_site_logo' => TRUE,
            'use_site_name' => TRUE,
            'use_site_slogan' => TRUE,
            'label_display' => FALSE,
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function blockForm($form, FormStateInterface $form_state) {
        // Get permissions.
        $url_system_theme_settings = new Url('system.theme_settings');
        if ($url_system_theme_settings->access()) {
            // Provide links to the Appearance Settings page if the user has access to
            // administer themes.
            $site_logo_description = $this->t('Defined on the <a href="@appearance">Appearance Settings</a> page.', [
                '@appearance' => $url_system_theme_settings->toString(),
            ]);
        }
        else {
            // Explain that the user does not have access to the Appearance and Theme
            // Settings pages.
            $site_logo_description = $this->t('Defined on the Appearance or Theme Settings page. You do not have the appropriate permissions to change the site logo.');
        }
        $url_system_site_information_settings = new Url('system.site_information_settings');
        if ($url_system_site_information_settings->access()) {
            // Get paths to settings pages.
            $site_information_url = $url_system_site_information_settings->toString();
            // Provide link to Site Information page if the user has access to
            // administer site configuration.
            $site_name_description = $this->t('Defined on the <a href=":information">Site Information</a> page.', [
                ':information' => $site_information_url,
            ]);
            $site_slogan_description = $this->t('Defined on the <a href=":information">Site Information</a> page.', [
                ':information' => $site_information_url,
            ]);
        }
        else {
            // Explain that the user does not have access to the Site Information
            // page.
            $site_name_description = $this->t('Defined on the Site Information page. You do not have the appropriate permissions to change the site logo.');
            $site_slogan_description = $this->t('Defined on the Site Information page. You do not have the appropriate permissions to change the site logo.');
        }
        $form['block_branding'] = [
            '#type' => 'fieldset',
            '#title' => $this->t('Toggle branding elements'),
            '#description' => $this->t('Choose which branding elements you want to show in this block instance.'),
        ];
        $form['block_branding']['use_site_logo'] = [
            '#type' => 'checkbox',
            '#title' => $this->t('Site logo'),
            '#description' => $site_logo_description,
            '#default_value' => $this->configuration['use_site_logo'],
        ];
        $form['block_branding']['use_site_name'] = [
            '#type' => 'checkbox',
            '#title' => $this->t('Site name'),
            '#description' => $site_name_description,
            '#default_value' => $this->configuration['use_site_name'],
        ];
        $form['block_branding']['use_site_slogan'] = [
            '#type' => 'checkbox',
            '#title' => $this->t('Site slogan'),
            '#description' => $site_slogan_description,
            '#default_value' => $this->configuration['use_site_slogan'],
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function blockSubmit($form, FormStateInterface $form_state) {
        $block_branding = $form_state->getValue('block_branding');
        $this->configuration['use_site_logo'] = $block_branding['use_site_logo'];
        $this->configuration['use_site_name'] = $block_branding['use_site_name'];
        $this->configuration['use_site_slogan'] = $block_branding['use_site_slogan'];
    }
    
    /**
     * {@inheritdoc}
     */
    public function build() {
        $build = [];
        $site_config = $this->configFactory
            ->get('system.site');
        $build['site_logo'] = [
            '#theme' => 'image',
            '#uri' => theme_get_setting('logo.url'),
            '#alt' => $this->t('Home'),
            '#access' => $this->configuration['use_site_logo'],
        ];
        $build['site_name'] = [
            '#markup' => $site_config->get('name'),
            '#access' => $this->configuration['use_site_name'],
        ];
        $build['site_slogan'] = [
            '#markup' => $site_config->get('slogan'),
            '#access' => $this->configuration['use_site_slogan'],
        ];
        return $build;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCacheTags() {
        return Cache::mergeTags(parent::getCacheTags(), $this->configFactory
            ->get('system.site')
            ->getCacheTags());
    }

}