class SettingsForm

class SettingsForm extends ConfigFormBase {
    
    /**
     * The AdvAgg cache.
     *
     * @var \Drupal\Core\Cache\CacheBackendInterface
     */
    protected $cache;
    
    /**
     * Constructs a SettingsForm object.
     *
     * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
     *   The factory for configuration objects.
     * @param \Drupal\Core\Cache\CacheBackendInterface $cache
     *   The AdvAgg cache 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_css_minify_settings';
    }
    
    /**
     * {@inheritdoc}
     */
    protected function getEditableConfigNames() {
        return [
            'advagg_css_minify.settings',
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        
        /** @var \Drupal\Core\Config\Config $config */
        $config = $this->config('advagg_css_minify.settings');
        $form = [];
        if ($this->config('advagg.settings')
            ->get('cache_level') === 0) {
            $form['advagg_devel_msg'] = [
                '#markup' => '<p>' . $this->t('The settings below will not have any effect because AdvAgg is currently in <a href="@devel">development mode</a>. Once the cache settings have been set to a non-development level, CSS minification will take place.', [
                    '@devel' => Url::fromRoute('advagg.settings', [], [
                        'fragment' => 'edit-advagg-cache-level',
                    ])->toString(),
                ]) . '</p>',
            ];
        }
        $options = [
            0 => $this->t('Disabled'),
            1 => $this->t('Core'),
            2 => $this->t('YUI Compressor'),
        ];
        $form['minifier'] = [
            '#type' => 'radios',
            '#title' => $this->t('Minification: Select a minifier'),
            '#default_value' => $config->get('minifier'),
            '#options' => $options,
        ];
        $form['add_license'] = [
            '#type' => 'checkbox',
            '#title' => $this->t('Add licensing comments'),
            '#default_value' => $config->get('add_license'),
            '#description' => $this->t("If unchecked, the Advanced Aggregation module's licensing comments\n      will be omitted from the aggregated files. Omitting the comments will produce somewhat better scores in\n      some automated security scans but otherwise should not affect your site. These are included by default in order to better follow the spirit of the GPL by providing the source for javascript files."),
        ];
        return parent::buildForm($form, $form_state);
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        
        /** @var \Drupal\Core\Config\Config $config */
        $config = $this->config('advagg_css_minify.settings');
        // Clear Caches.
        Cache::invalidateTags([
            'library_info',
        ]);
        $this->cache
            ->invalidateAll();
        // Save settings.
        $config->set('add_license', $form_state->getValue('add_license'))
            ->set('minifier', $form_state->getValue('minifier'))
            ->save();
        parent::submitForm($form, $form_state);
    }

}