class CurrentThemeCondition

class CurrentThemeCondition extends ConditionPluginBase implements ContainerFactoryPluginInterface {
    
    /**
     * The theme manager.
     *
     * @var \Drupal\Core\Theme\ThemeManagerInterface
     */
    protected $themeManager;
    
    /**
     * The theme handler.
     *
     * @var \Drupal\Core\Extension\ThemeHandlerInterface
     */
    protected $themeHandler;
    
    /**
     * Constructs a CurrentThemeCondition condition plugin.
     *
     * @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\Theme\ThemeManagerInterface $theme_manager
     *   The theme manager.
     * @param \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler
     *   The theme handler.
     */
    public function __construct(array $configuration, $plugin_id, $plugin_definition, ThemeManagerInterface $theme_manager, ThemeHandlerInterface $theme_handler) {
        parent::__construct($configuration, $plugin_id, $plugin_definition);
        $this->themeManager = $theme_manager;
        $this->themeHandler = $theme_handler;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
        return new static($configuration, $plugin_id, $plugin_definition, $container->get('theme.manager'), $container->get('theme_handler'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function defaultConfiguration() {
        return [
            'theme' => '',
        ] + parent::defaultConfiguration();
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
        $form['theme'] = [
            '#type' => 'select',
            '#title' => $this->t('Theme'),
            '#default_value' => $this->configuration['theme'],
            '#options' => array_map(function ($theme_info) {
                return $theme_info->info['name'];
            }, $this->themeHandler
                ->listInfo()),
        ];
        return parent::buildConfigurationForm($form, $form_state);
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
        $this->configuration['theme'] = $form_state->getValue('theme');
        parent::submitConfigurationForm($form, $form_state);
    }
    
    /**
     * {@inheritdoc}
     */
    public function evaluate() {
        if (!$this->configuration['theme']) {
            return TRUE;
        }
        return $this->themeManager
            ->getActiveTheme()
            ->getName() == $this->configuration['theme'];
    }
    
    /**
     * {@inheritdoc}
     */
    public function summary() {
        if ($this->isNegated()) {
            return $this->t('The current theme is not @theme', [
                '@theme' => $this->configuration['theme'],
            ]);
        }
        return $this->t('The current theme is @theme', [
            '@theme' => $this->configuration['theme'],
        ]);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCacheContexts() {
        $contexts = parent::getCacheContexts();
        $contexts[] = 'theme';
        return $contexts;
    }

}