class CacheExampleForm

class CacheExampleForm extends FormBase {
    
    /**
     * The current user.
     *
     * @var \Drupal\Core\Session\AccountProxyInterface
     */
    protected $currentUser;
    
    /**
     * The cache.default cache backend.
     *
     * @var \Drupal\Core\Cache\CacheBackendInterface
     */
    protected $cacheBackend;
    
    /**
     * The date formatter service.
     *
     * @var \Drupal\Core\Datetime\DateFormatterInterface
     */
    protected $dateFormatter;
    
    /**
     * The file system service.
     *
     * @var \Drupal\Core\File\FileSystemInterface
     */
    protected $fileSystem;
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        // Forms that require a Drupal service or a custom service should access
        // the service using dependency injection.
        // @link https://www.drupal.org/node/2203931.
        // Those services are passed in the $container through the static create
        // method.
        $form = new static();
        $form->setRequestStack($container->get('request_stack'))
            ->setStringTranslation($container->get('string_translation'))
            ->setMessenger($container->get('messenger'));
        $form->currentUser = $container->get('current_user');
        $form->cacheBackend = $container->get('cache.default');
        $form->dateFormatter = $container->get('date.formatter');
        $form->fileSystem = $container->get('file_system');
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'cron_cache';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        // Log execution time.
        $start_time = microtime(TRUE);
        // Try to load the files count from cache. This function will accept two
        // arguments:
        // - cache object name (cid)
        // - cache bin, the (optional) cache bin (most often a database table) where
        //   the object is to be saved.
        //
        // cache_get() returns the cached object or FALSE if object does not exist.
        if ($cache = $this->cacheBackend
            ->get('cache_example_files_count')) {
            
            /*
             * Get cached data. Complex data types will be unserialized automatically.
             */
            $files_count = $cache->data;
        }
        else {
            // If there was no cached data available we have to search filesystem.
            // Recursively get all .PHP files from Drupal's core folder.
            $files_count = count($this->fileSystem
                ->scanDirectory('core', '/.php/'));
            // Since we have recalculated, we now need to store the new data into
            // cache. Complex data types will be automatically serialized before
            // being saved into cache.
            // Here we use the default setting and create an unexpiring cache item.
            // See below for an example that creates an expiring cache item.
            $this->cacheBackend
                ->set('cache_example_files_count', $files_count, CacheBackendInterface::CACHE_PERMANENT);
        }
        $end_time = microtime(TRUE);
        $duration = $end_time - $start_time;
        // Format intro message.
        $intro_message = '<p>' . $this->t("This example will search Drupal's core folder and display a count of the PHP files in it.") . ' ';
        $intro_message .= $this->t('This can take a while, since there are a lot of files to be searched.') . ' ';
        $intro_message .= $this->t('We will search filesystem just once and save output to the cache. We will use cached data for later requests.') . '</p>';
        $intro_message .= '<p>' . $this->t('<a href="@url">Reload this page</a> to see cache in action.', [
            '@url' => $this->getRequest()
                ->getRequestUri(),
        ]) . ' ';
        $intro_message .= $this->t('You can use the button below to remove cached data.') . '</p>';
        $form['file_search'] = [
            '#type' => 'fieldset',
            '#title' => $this->t('File search caching'),
        ];
        $form['file_search']['introduction'] = [
            '#markup' => $intro_message,
        ];
        $color = empty($cache) ? 'red' : 'green';
        $retrieval = empty($cache) ? $this->t('calculated by traversing the filesystem') : $this->t('retrieved from cache');
        $form['file_search']['statistics'] = [
            '#type' => 'item',
            '#markup' => $this->t('%count files exist in this Drupal installation; @retrieval in @time ms. <br/>(Source: <span style="color:@color;">@source</span>)', [
                '%count' => $files_count,
                '@retrieval' => $retrieval,
                '@time' => number_format($duration * 1000, 2),
                '@color' => $color,
                '@source' => empty($cache) ? $this->t('actual file search') : $this->t('cached'),
            ]),
        ];
        $form['file_search']['remove_file_count'] = [
            '#type' => 'submit',
            '#submit' => [
                '::expireFiles',
            ],
            '#value' => $this->t('Explicitly remove cached file count'),
        ];
        $form['expiration_demo'] = [
            '#type' => 'fieldset',
            '#title' => $this->t('Cache expiration settings'),
        ];
        $form['expiration_demo']['explanation'] = [
            '#markup' => $this->t('A cache item can be set as CACHE_PERMANENT, meaning that it will only be removed when explicitly cleared, or it can have an expiration time (a Unix timestamp).'),
        ];
        $item = $this->cacheBackend
            ->get('cache_example_expiring_item', TRUE);
        if ($item == FALSE) {
            $item_status = $this->t('Cache item does not exist');
        }
        else {
            $item_status = $item->valid ? $this->t('Cache item exists and is set to expire at %time', [
                '%time' => $item->data,
            ]) : $this->t('Cache_item is invalid');
        }
        $form['expiration_demo']['current_status'] = [
            '#type' => 'item',
            '#title' => $this->t('Current status of cache item "cache_example_expiring_item"'),
            '#markup' => $item_status,
        ];
        $form['expiration_demo']['expiration'] = [
            '#type' => 'select',
            '#title' => $this->t('Time before cache expiration'),
            '#options' => [
                'never_remove' => $this->t('CACHE_PERMANENT'),
                -10 => $this->t('Immediate expiration'),
                10 => $this->t('10 seconds from form submission'),
                60 => $this->t('1 minute from form submission'),
                300 => $this->t('5 minutes from form submission'),
            ],
            '#default_value' => -10,
            '#description' => $this->t('Any cache item can be set to only expire when explicitly cleared, or to expire at a given time.'),
        ];
        $form['expiration_demo']['create_cache_item'] = [
            '#type' => 'submit',
            '#value' => $this->t('Create a cache item with this expiration'),
            '#submit' => [
                '::createExpiringItem',
            ],
        ];
        $form['cache_clearing'] = [
            '#type' => 'fieldset',
            '#title' => $this->t('Expire and remove options'),
            '#description' => $this->t("We have APIs to expire cached items and also to just remove them. Unfortunately, they're all the same API, cache_clear_all"),
        ];
        $form['cache_clearing']['cache_clear_type'] = [
            '#type' => 'radios',
            '#title' => $this->t('Type of cache clearing to do'),
            '#options' => [
                'expire' => $this->t('Remove items from the "cache" bin that have expired'),
                'remove_all' => $this->t('Remove all items from the "cache" bin regardless of expiration'),
                'remove_tag' => $this->t('Remove all items in the "cache" bin with the tag "cache_example" set to 1'),
            ],
            '#default_value' => 'expire',
        ];
        // Submit button to clear cached data.
        $form['cache_clearing']['clear_expired'] = [
            '#type' => 'submit',
            '#value' => $this->t('Clear or expire cache'),
            '#submit' => [
                '::cacheClearing',
            ],
            '#access' => $this->currentUser
                ->hasPermission('administer site configuration'),
        ];
        return $form;
    }
    
    /**
     * Submit handler that explicitly clears cache_example_files_count from cache.
     */
    public function expireFiles($form, &$form_state) {
        // Clear cached data. This function will delete cached object from cache
        // bin.
        //
        // The first argument is cache id to be deleted. Since we've provided it
        // explicitly, it will be removed whether or not it has an associated
        // expiration time. The second argument (required here) is the cache bin.
        // Using cache_clear_all() explicitly in this way
        // forces removal of the cached item.
        $this->cacheBackend
            ->delete('cache_example_files_count');
        // Display message to the user.
        $this->messenger()
            ->addMessage($this->t('Cached data key "cache_example_files_count" was cleared.'), 'status');
    }
    
    /**
     * Submit handler to create a new cache item with specified expiration.
     */
    public function createExpiringItem($form, &$form_state) {
        $tags = [
            'cache_example:1',
        ];
        $interval = $form_state->getValue('expiration');
        if ($interval == 'never_remove') {
            $expiration = CacheBackendInterface::CACHE_PERMANENT;
            $expiration_friendly = $this->t('Never expires');
        }
        else {
            $expiration = time() + $interval;
            $expiration_friendly = $this->dateFormatter
                ->format($expiration);
        }
        // Set the expiration to the actual Unix timestamp of the end of the
        // required interval. Also add a tag to it to be able to clear caches more
        // precise.
        $this->cacheBackend
            ->set('cache_example_expiring_item', $expiration_friendly, $expiration, $tags);
        $this->messenger()
            ->addMessage($this->t('cache_example_expiring_item was set to expire at %time', [
            '%time' => $expiration_friendly,
        ]));
    }
    
    /**
     * Submit handler to demonstrate the various uses of cache_clear_all().
     */
    public function cacheClearing($form, &$form_state) {
        switch ($form_state->getValue('cache_clear_type')) {
            case 'expire':
                // Here we'll remove all cache keys in the 'cache' bin that have
                // expired.
                $this->cacheBackend
                    ->garbageCollection();
                $this->messenger()
                    ->addMessage($this->t('\\Drupal::cache()->garbageCollection() was called, removing any expired cache items.'));
                break;
            case 'remove_all':
                // This removes all keys in a bin using a super-wildcard. This
                // has nothing to do with expiration. It's just brute-force removal.
                $this->cacheBackend
                    ->deleteAll();
                $this->messenger()
                    ->addMessage($this->t('ALL entries in the "cache" bin were removed with \\Drupal::cache()->deleteAll().'));
                break;
            case 'remove_tag':
                // This removes cache entries with the tag "cache_example" set to 1 in
                // the "cache".
                $tags = [
                    'cache_example:1',
                ];
                Cache::invalidateTags($tags);
                $this->messenger()
                    ->addMessage($this->t('Cache entries with the tag "cache_example" set to 1 in the "cache" bin were invalidated with \\Drupal\\Core\\Cache\\Cache::invalidateTags($tags).'));
                break;
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
    }

}