class File

class File extends FieldPluginBase {
    
    /**
     * {@inheritdoc}
     */
    public function init(ViewExecutable $view, DisplayPluginBase $display, array &$options = NULL) {
        parent::init($view, $display, $options);
        if (!empty($options['link_to_file'])) {
            $this->additional_fields['uri'] = 'uri';
        }
    }
    
    /**
     * {@inheritdoc}
     */
    protected function defineOptions() {
        $options = parent::defineOptions();
        $options['link_to_file'] = [
            'default' => FALSE,
        ];
        return $options;
    }
    
    /**
     * Provide link to file option
     */
    public function buildOptionsForm(&$form, FormStateInterface $form_state) {
        $form['link_to_file'] = [
            '#title' => $this->t('Link this field to download the file'),
            '#description' => $this->t("Enable to override this field's links."),
            '#type' => 'checkbox',
            '#default_value' => !empty($this->options['link_to_file']),
        ];
        parent::buildOptionsForm($form, $form_state);
    }
    
    /**
     * Prepares link to the file.
     *
     * @param string $data
     *   The XSS safe string for the link text.
     * @param \Drupal\views\ResultRow $values
     *   The values retrieved from a single row of a view's query result.
     *
     * @return string
     *   Returns a string for the link text.
     */
    protected function renderLink($data, ResultRow $values) {
        if (!empty($this->options['link_to_file']) && $data !== NULL && $data !== '') {
            $this->options['alter']['make_link'] = TRUE;
            // @todo Wrap in file_url_transform_relative(). This is currently
            // impossible. As a work-around, we could add the 'url.site' cache context
            // to ensure different file URLs are generated for different sites in a
            // multisite setup, including HTTP and HTTPS versions of the same site.
            // But unfortunately it's impossible to bubble a cache context here.
            // Fix in https://www.drupal.org/node/2646744.
            $this->options['alter']['path'] = file_create_url($this->getValue($values, 'uri'));
        }
        return $data;
    }
    
    /**
     * {@inheritdoc}
     */
    public function render(ResultRow $values) {
        $value = $this->getValue($values);
        return $this->renderLink($this->sanitizeValue($value), $values);
    }

}