class Language

class Language extends ConditionPluginBase implements ContainerFactoryPluginInterface {
    
    /**
     * The Language manager.
     *
     * @var \Drupal\Core\Language\LanguageManagerInterface
     */
    protected $languageManager;
    
    /**
     * Creates a new Language instance.
     *
     * @param \Drupal\Core\Language\LanguageManagerInterface $language_manager
     *   The language manager.
     * @param array $configuration
     *   The plugin configuration, i.e. an array with configuration values keyed
     *   by configuration option name. The special key 'context' may be used to
     *   initialize the defined contexts by setting it to an array of context
     *   values keyed by context names.
     * @param string $plugin_id
     *   The plugin ID for the plugin instance.
     * @param mixed $plugin_definition
     *   The plugin implementation definition.
     */
    public function __construct(LanguageManagerInterface $language_manager, array $configuration, $plugin_id, $plugin_definition) {
        parent::__construct($configuration, $plugin_id, $plugin_definition);
        $this->languageManager = $language_manager;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
        return new static($container->get('language_manager'), $configuration, $plugin_id, $plugin_definition);
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
        if ($this->languageManager
            ->isMultilingual()) {
            // Fetch languages.
            $languages = $this->languageManager
                ->getLanguages();
            $langcodes_options = [];
            foreach ($languages as $language) {
                $langcodes_options[$language->getId()] = $language->getName();
            }
            $form['langcodes'] = [
                '#type' => 'checkboxes',
                '#title' => $this->t('Language selection'),
                '#default_value' => $this->configuration['langcodes'],
                '#options' => $langcodes_options,
                '#description' => $this->t('Select languages to enforce. If none are selected, all languages will be allowed.'),
            ];
        }
        else {
            $form['langcodes'] = [
                '#type' => 'value',
                '#default_value' => $this->configuration['langcodes'],
            ];
        }
        return parent::buildConfigurationForm($form, $form_state);
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
        $this->configuration['langcodes'] = array_filter($form_state->getValue('langcodes'));
        parent::submitConfigurationForm($form, $form_state);
    }
    
    /**
     * {@inheritdoc}
     */
    public function summary() {
        $language_list = $this->languageManager
            ->getLanguages(LanguageInterface::STATE_ALL);
        $selected = $this->configuration['langcodes'];
        // Reduce the language list to an array of language names.
        $language_names = array_reduce($language_list, function ($result, $item) use ($selected) {
            // If the current item of the $language_list array is one of the selected
            // languages, add it to the $results array.
            if (!empty($selected[$item->getId()])) {
                $result[$item->getId()] = $item->getName();
            }
            return $result;
        }, []);
        // If we have more than one language selected, separate them by commas.
        if (count($this->configuration['langcodes']) > 1) {
            $languages = implode(', ', $language_names);
        }
        else {
            // If we have just one language just grab the only present value.
            $languages = array_pop($language_names);
        }
        if (!empty($this->configuration['negate'])) {
            return $this->t('The language is not @languages.', [
                '@languages' => $languages,
            ]);
        }
        return $this->t('The language is @languages.', [
            '@languages' => $languages,
        ]);
    }
    
    /**
     * {@inheritdoc}
     */
    public function evaluate() {
        if (empty($this->configuration['langcodes']) && !$this->isNegated()) {
            return TRUE;
        }
        $language = $this->getContextValue('language');
        // Language visibility settings.
        return !empty($this->configuration['langcodes'][$language->getId()]);
    }
    
    /**
     * {@inheritdoc}
     */
    public function defaultConfiguration() {
        return [
            'langcodes' => [],
        ] + parent::defaultConfiguration();
    }

}