class PerformanceForm

class PerformanceForm extends ConfigFormBase {
    
    /**
     * The date formatter service.
     *
     * @var \Drupal\Core\Datetime\DateFormatterInterface
     */
    protected $dateFormatter;
    
    /**
     * The CSS asset collection optimizer service.
     *
     * @var \Drupal\Core\Asset\AssetCollectionOptimizerInterface
     */
    protected $cssCollectionOptimizer;
    
    /**
     * The JavaScript asset collection optimizer service.
     *
     * @var \Drupal\Core\Asset\AssetCollectionOptimizerInterface
     */
    protected $jsCollectionOptimizer;
    
    /**
     * The module handler.
     *
     * @var \Drupal\Core\Extension\ModuleHandlerInterface
     */
    protected $moduleHandler;
    
    /**
     * Constructs a PerformanceForm object.
     *
     * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
     *   The factory for configuration objects.
     * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
     *   The date formatter service.
     * @param \Drupal\Core\Asset\AssetCollectionOptimizerInterface $css_collection_optimizer
     *   The CSS asset collection optimizer service.
     * @param \Drupal\Core\Asset\AssetCollectionOptimizerInterface $js_collection_optimizer
     *   The JavaScript asset collection optimizer service.
     * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
     *   The module handler.
     */
    public function __construct(ConfigFactoryInterface $config_factory, DateFormatterInterface $date_formatter, AssetCollectionOptimizerInterface $css_collection_optimizer, AssetCollectionOptimizerInterface $js_collection_optimizer, ModuleHandlerInterface $module_handler) {
        parent::__construct($config_factory);
        $this->dateFormatter = $date_formatter;
        $this->cssCollectionOptimizer = $css_collection_optimizer;
        $this->jsCollectionOptimizer = $js_collection_optimizer;
        $this->moduleHandler = $module_handler;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('config.factory'), $container->get('date.formatter'), $container->get('asset.css.collection_optimizer'), $container->get('asset.js.collection_optimizer'), $container->get('module_handler'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'system_performance_settings';
    }
    
    /**
     * {@inheritdoc}
     */
    protected function getEditableConfigNames() {
        return [
            'system.performance',
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $form['#attached']['library'][] = 'system/drupal.system';
        $config = $this->config('system.performance');
        $form['clear_cache'] = [
            '#type' => 'details',
            '#title' => t('Clear cache'),
            '#open' => TRUE,
        ];
        $form['clear_cache']['clear'] = [
            '#type' => 'submit',
            '#value' => t('Clear all caches'),
            '#submit' => [
                '::submitCacheClear',
            ],
        ];
        $form['caching'] = [
            '#type' => 'details',
            '#title' => t('Caching'),
            '#open' => TRUE,
        ];
        // Identical options to the ones for block caching.
        // @see \Drupal\Core\Block\BlockBase::buildConfigurationForm()
        $period = [
            0,
            60,
            180,
            300,
            600,
            900,
            1800,
            2700,
            3600,
            10800,
            21600,
            32400,
            43200,
            86400,
        ];
        $period = array_map([
            $this->dateFormatter,
            'formatInterval',
        ], array_combine($period, $period));
        $period[0] = '<' . t('no caching') . '>';
        $form['caching']['page_cache_maximum_age'] = [
            '#type' => 'select',
            '#title' => t('Browser and proxy cache maximum age'),
            '#default_value' => $config->get('cache.page.max_age'),
            '#options' => $period,
            '#description' => t('This is used as the value for max-age in Cache-Control headers.'),
        ];
        $form['caching']['internal_page_cache'] = [
            '#markup' => $this->t('Drupal provides an <a href=":module_enable">Internal Page Cache module</a> that is recommended for small to medium-sized websites.', [
                ':module_enable' => Url::fromRoute('system.modules_list')->toString(),
            ]),
            '#access' => !$this->moduleHandler
                ->moduleExists('page_cache'),
        ];
        $directory = 'public://';
        $is_writable = is_dir($directory) && is_writable($directory);
        $disabled = !$is_writable;
        $disabled_message = '';
        if (!$is_writable) {
            $disabled_message = ' ' . t('<strong class="error">Set up the <a href=":file-system">public files directory</a> to make these optimizations available.</strong>', [
                ':file-system' => Url::fromRoute('system.file_system_settings')->toString(),
            ]);
        }
        $form['bandwidth_optimization'] = [
            '#type' => 'details',
            '#title' => t('Bandwidth optimization'),
            '#open' => TRUE,
            '#description' => t('External resources can be optimized automatically, which can reduce both the size and number of requests made to your website.') . $disabled_message,
        ];
        $form['bandwidth_optimization']['preprocess_css'] = [
            '#type' => 'checkbox',
            '#title' => t('Aggregate CSS files'),
            '#default_value' => $config->get('css.preprocess'),
            '#disabled' => $disabled,
        ];
        $form['bandwidth_optimization']['preprocess_js'] = [
            '#type' => 'checkbox',
            '#title' => t('Aggregate JavaScript files'),
            '#default_value' => $config->get('js.preprocess'),
            '#disabled' => $disabled,
        ];
        return parent::buildForm($form, $form_state);
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $this->cssCollectionOptimizer
            ->deleteAll();
        $this->jsCollectionOptimizer
            ->deleteAll();
        $this->config('system.performance')
            ->set('cache.page.max_age', $form_state->getValue('page_cache_maximum_age'))
            ->set('css.preprocess', $form_state->getValue('preprocess_css'))
            ->set('js.preprocess', $form_state->getValue('preprocess_js'))
            ->save();
        parent::submitForm($form, $form_state);
    }
    
    /**
     * Clears the caches.
     */
    public function submitCacheClear(array &$form, FormStateInterface $form_state) {
        drupal_flush_all_caches();
        $this->messenger()
            ->addStatus($this->t('Caches cleared.'));
    }

}