class ViewsBlockBase

abstract class ViewsBlockBase extends BlockBase implements ContainerFactoryPluginInterface {
    
    /**
     * The View executable object.
     *
     * @var \Drupal\views\ViewExecutable
     */
    protected $view;
    
    /**
     * The display ID being used for this View.
     *
     * @var string
     */
    protected $displayID;
    
    /**
     * Indicates whether the display was successfully set.
     *
     * @var bool
     */
    protected $displaySet;
    
    /**
     * The current user.
     *
     * @var \Drupal\Core\Session\AccountInterface
     */
    protected $user;
    
    /**
     * Constructs a \Drupal\views\Plugin\Block\ViewsBlockBase object.
     *
     * @param array $configuration
     *   A configuration array containing information about the plugin instance.
     * @param string $plugin_id
     *   The plugin_id for the plugin instance.
     * @param mixed $plugin_definition
     *   The plugin implementation definition.
     * @param \Drupal\views\ViewExecutableFactory $executable_factory
     *   The view executable factory.
     * @param \Drupal\Core\Entity\EntityStorageInterface $storage
     *   The views storage.
     * @param \Drupal\Core\Session\AccountInterface $user
     *   The current user.
     */
    public function __construct(array $configuration, $plugin_id, $plugin_definition, ViewExecutableFactory $executable_factory, EntityStorageInterface $storage, AccountInterface $user) {
        $this->pluginId = $plugin_id;
        $delta = $this->getDerivativeId();
        list($name, $this->displayID) = explode('-', $delta, 2);
        // Load the view.
        $view = $storage->load($name);
        $this->view = $executable_factory->get($view);
        $this->displaySet = $this->view
            ->setDisplay($this->displayID);
        $this->user = $user;
        parent::__construct($configuration, $plugin_id, $plugin_definition);
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
        return new static($configuration, $plugin_id, $plugin_definition, $container->get('views.executable'), $container->get('entity_type.manager')
            ->getStorage('view'), $container->get('current_user'));
    }
    
    /**
     * {@inheritdoc}
     */
    protected function blockAccess(AccountInterface $account) {
        if ($this->view
            ->access($this->displayID)) {
            $access = AccessResult::allowed();
        }
        else {
            $access = AccessResult::forbidden();
        }
        return $access;
    }
    
    /**
     * {@inheritdoc}
     */
    public function defaultConfiguration() {
        return [
            'views_label' => '',
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function getPreviewFallbackString() {
        if (!empty($this->pluginDefinition["admin_label"])) {
            return $this->t('"@view" views block', [
                '@view' => $this->pluginDefinition["admin_label"],
            ]);
        }
        else {
            return $this->t('"@view" views block', [
                '@view' => $this->view->storage
                    ->label() . '::' . $this->displayID,
            ]);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
        $form = parent::buildConfigurationForm($form, $form_state);
        // Set the default label to '' so the views internal title is used.
        $form['label']['#default_value'] = '';
        $form['label']['#access'] = FALSE;
        // Unset the machine_name provided by BlockForm.
        unset($form['id']['#machine_name']['source']);
        // Prevent users from changing the auto-generated block machine_name.
        $form['id']['#access'] = FALSE;
        $form['#pre_render'][] = '\\Drupal\\views\\Plugin\\views\\PluginBase::preRenderAddFieldsetMarkup';
        // Allow to override the label on the actual page.
        $form['views_label_checkbox'] = [
            '#type' => 'checkbox',
            '#title' => $this->t('Override title'),
            '#default_value' => !empty($this->configuration['views_label']),
        ];
        $form['views_label_fieldset'] = [
            '#type' => 'fieldset',
            '#states' => [
                'visible' => [
                    [
                        ':input[name="settings[views_label_checkbox]"]' => [
                            'checked' => TRUE,
                        ],
                    ],
                ],
            ],
        ];
        $form['views_label'] = [
            '#title' => $this->t('Title'),
            '#type' => 'textfield',
            '#default_value' => $this->configuration['views_label'] ?: $this->view
                ->getTitle(),
            '#states' => [
                'visible' => [
                    [
                        ':input[name="settings[views_label_checkbox]"]' => [
                            'checked' => TRUE,
                        ],
                    ],
                ],
            ],
            '#fieldset' => 'views_label_fieldset',
        ];
        if ($this->view->storage
            ->access('edit') && \Drupal::moduleHandler()->moduleExists('views_ui')) {
            $form['views_label']['#description'] = $this->t('Changing the title here means it cannot be dynamically altered anymore. (Try changing it directly in <a href=":url">@name</a>.)', [
                ':url' => Url::fromRoute('entity.view.edit_display_form', [
                    'view' => $this->view->storage
                        ->id(),
                    'display_id' => $this->displayID,
                ])
                    ->toString(),
                '@name' => $this->view->storage
                    ->label(),
            ]);
        }
        else {
            $form['views_label']['#description'] = $this->t('Changing the title here means it cannot be dynamically altered anymore.');
        }
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function blockSubmit($form, FormStateInterface $form_state) {
        if (!$form_state->isValueEmpty('views_label_checkbox')) {
            $this->configuration['views_label'] = $form_state->getValue('views_label');
        }
        else {
            $this->configuration['views_label'] = '';
        }
        $form_state->unsetValue('views_label_checkbox');
    }
    
    /**
     * Converts Views block content to a renderable array with contextual links.
     *
     * @param string|array $output
     *   An string|array representing the block. This will be modified to be a
     *   renderable array, containing the optional '#contextual_links' property (if
     *   there are any contextual links associated with the block).
     * @param string $block_type
     *   The type of the block. If it's 'block' it's a regular views display,
     *   but 'exposed_filter' exist as well.
     */
    protected function addContextualLinks(&$output, $block_type = 'block') {
        // Do not add contextual links to an empty block.
        if (!empty($output)) {
            // Contextual links only work on blocks whose content is a renderable
            // array, so if the block contains a string of already-rendered markup,
            // convert it to an array.
            if (is_string($output)) {
                $output = [
                    '#markup' => $output,
                ];
            }
            // views_add_contextual_links() needs the following information in
            // order to be attached to the view.
            $output['#view_id'] = $this->view->storage
                ->id();
            $output['#view_display_show_admin_links'] = $this->view
                ->getShowAdminLinks();
            $output['#view_display_plugin_id'] = $this->view->display_handler
                ->getPluginId();
            views_add_contextual_links($output, $block_type, $this->displayID);
        }
    }
    
    /**
     * Gets the view executable.
     *
     * @return \Drupal\views\ViewExecutable
     *   The view executable.
     *
     * @todo revisit after https://www.drupal.org/node/3027653. This method was
     *   added in https://www.drupal.org/node/3002608, but should not be
     *   necessary once block plugins can determine if they are being previewed.
     */
    public function getViewExecutable() {
        return $this->view;
    }

}