class SettingsForm

class SettingsForm extends ConfigFormBase {
    
    /**
     * The Advagg cache.
     *
     * @var \Drupal\Core\Cache\CacheBackendInterface
     */
    protected $cache;
    
    /**
     * The module handler service.
     *
     * @var \Drupal\Core\Extension\ModuleHandlerInterface
     */
    protected $moduleHandler;
    
    /**
     * The core language manager service.
     *
     * @var \Drupal\Core\Language\LanguageManagerInterface
     */
    protected $languageManager;
    
    /**
     * Constructs a SettingsForm object.
     *
     * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
     *   The factory for configuration objects.
     * @param \Drupal\Core\Cache\CacheBackendInterface $cache
     *   The JavaScript asset collection optimizer service.
     */
    public function __construct(ConfigFactoryInterface $config_factory, CacheBackendInterface $cache) {
        parent::__construct($config_factory);
        $this->cache = $cache;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('config.factory'), $container->get('cache.advagg'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'advagg_old_ie_compatibility_settings';
    }
    
    /**
     * {@inheritdoc}
     */
    protected function getEditableConfigNames() {
        return [
            'advagg_old_ie_compatibility.settings',
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $config = $this->config('advagg_old_ie_compatibility.settings');
        $form['active'] = [
            '#type' => 'checkbox',
            '#title' => $this->t('Prevent more than %limit CSS selectors in an aggregated CSS file', [
                '%limit' => $config->get('limit'),
            ]),
            '#default_value' => $config->get('active'),
            '#description' => $this->t('Internet Explorer before version 10; IE9, IE8, IE7, and IE6 all have 4095 as the limit for the maximum number of css selectors that can be in a file. Enabling this will prevent CSS aggregates from being created that exceed this limit. <a href="@link">More info</a>.', [
                '@link' => 'http://blogs.msdn.com/b/ieinternals/archive/2011/05/14/10164546.aspx',
            ]),
        ];
        $form['limit'] = [
            '#type' => 'textfield',
            '#title' => $this->t('The selector count the IE CSS limiter should use'),
            '#default_value' => $config->get('limit'),
            '#description' => $this->t('Internet Explorer before version 10; IE9, IE8, IE7, and IE6 all have 4095 as the limit for the maximum number of css selectors that can be in a file. Use this field to modify the value used.'),
            '#states' => [
                'visible' => [
                    '#edit-active' => [
                        'checked' => TRUE,
                    ],
                ],
                'disabled' => [
                    '#edit-active' => [
                        'checked' => FALSE,
                    ],
                ],
            ],
        ];
        return parent::buildForm($form, $form_state);
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        
        /** @var \Drupal\Core\Config\Config $config */
        $config = $this->config('advagg_old_ie_compatibility.settings');
        $config->set('active', $form_state->getValue('active'))
            ->set('limit', $form_state->getValue('limit'))
            ->save();
        // Clear relevant caches.
        Cache::invalidateTags([
            'library_info',
        ]);
        $this->cache
            ->invalidateAll();
        parent::submitForm($form, $form_state);
    }

}