class Block

class Block extends DisplayPluginBase {
  
  /**
   * Whether the display allows attachments.
   *
   * @var bool
   */
  protected $usesAttachments = TRUE;
  
  /**
   * The entity type manager.
   *
   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
   */
  protected $entityTypeManager;
  
  /**
   * The block manager.
   *
   * @var \Drupal\Core\Block\BlockManagerInterface
   */
  protected $blockManager;
  
  /**
   * Constructs a new Block instance.
   *
   * @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\Core\Entity\EntityTypeManagerInterface $entity_type_manager
   *   The entity type manager.
   * @param \Drupal\Core\Block\BlockManagerInterface $block_manager
   *   The block manager.
   */
  public function __construct(array $configuration, $plugin_id, $plugin_definition, EntityTypeManagerInterface $entity_type_manager, BlockManagerInterface $block_manager) {
    parent::__construct($configuration, $plugin_id, $plugin_definition);
    $this->entityTypeManager = $entity_type_manager;
    $this->blockManager = $block_manager;
  }
  
  /**
   * {@inheritdoc}
   */
  protected function defineOptions() {
    $options = parent::defineOptions();
    $options['block_description'] = [
      'default' => '',
    ];
    $options['block_category'] = [
      'default' => $this->t('Lists (Views)'),
    ];
    $options['block_hide_empty'] = [
      'default' => FALSE,
    ];
    $options['allow'] = [
      'contains' => [
        'items_per_page' => [
          'default' => 'items_per_page',
        ],
      ],
    ];
    return $options;
  }
  
  /**
   * Returns plugin-specific settings for the block.
   *
   * @param array $settings
   *   The settings of the block.
   *
   * @return array
   *   An array of block-specific settings to override the defaults provided in
   *   \Drupal\views\Plugin\Block\ViewsBlock::defaultConfiguration().
   *
   * @see \Drupal\views\Plugin\Block\ViewsBlock::defaultConfiguration()
   */
  public function blockSettings(array $settings) {
    $settings['items_per_page'] = NULL;
    return $settings;
  }
  
  /**
   * The display block handler returns the structure necessary for a block.
   */
  public function execute() {
    // Prior to this being called, the $view should already be set to this
    // display, and arguments should be set on the view.
    $element = $this->view
      ->render();
    if ($this->outputIsEmpty() && $this->getOption('block_hide_empty') && empty($this->view->style_plugin->definition['even empty'])) {
      return [];
    }
    else {
      return $element;
    }
  }
  
  /**
   * Provide the summary for page options in the views UI.
   *
   * This output is returned as an array.
   */
  public function optionsSummary(&$categories, &$options) {
    parent::optionsSummary($categories, $options);
    $categories['block'] = [
      'title' => $this->t('Block settings'),
      'column' => 'second',
      'build' => [
        '#weight' => -10,
      ],
    ];
    $block_description = strip_tags($this->getOption('block_description'));
    if (empty($block_description)) {
      $block_description = $this->t('None');
    }
    $block_category = $this->getOption('block_category');
    $options['block_description'] = [
      'category' => 'block',
      'title' => $this->t('Block name'),
      'value' => Unicode::truncate($block_description, 24, FALSE, TRUE),
    ];
    $options['block_category'] = [
      'category' => 'block',
      'title' => $this->t('Block category'),
      'value' => Unicode::truncate($block_category, 24, FALSE, TRUE),
    ];
    $filtered_allow = array_filter($this->getOption('allow'));
    $options['allow'] = [
      'category' => 'block',
      'title' => $this->t('Allow settings'),
      'value' => empty($filtered_allow) ? $this->t('None') : $this->t('Items per page'),
    ];
    $options['block_hide_empty'] = [
      'category' => 'other',
      'title' => $this->t('Hide block if the view output is empty'),
      'value' => $this->getOption('block_hide_empty') ? $this->t('Yes') : $this->t('No'),
    ];
  }
  
  /**
   * Provide the default form for setting options.
   */
  public function buildOptionsForm(&$form, FormStateInterface $form_state) {
    parent::buildOptionsForm($form, $form_state);
    switch ($form_state->get('section')) {
      case 'block_description':
        $form['#title'] .= $this->t('Block admin description');
        $form['block_description'] = [
          '#type' => 'textfield',
          '#description' => $this->t('This will appear as the name of this block in administer >> structure >> blocks.'),
          '#default_value' => $this->getOption('block_description'),
        ];
        break;

      case 'block_category':
        $form['#title'] .= $this->t('Block category');
        $form['block_category'] = [
          '#type' => 'textfield',
          '#autocomplete_route_name' => 'block.category_autocomplete',
          '#description' => $this->t('The category this block will appear under on the <a href=":href">blocks placement page</a>.', [
            ':href' => Url::fromRoute('block.admin_display')->toString(),
          ]),
          '#default_value' => $this->getOption('block_category'),
        ];
        break;

      case 'block_hide_empty':
        $form['#title'] .= $this->t('Block empty settings');
        $form['block_hide_empty'] = [
          '#title' => $this->t('Hide block if no result/empty text'),
          '#type' => 'checkbox',
          '#description' => $this->t('Hide the block if there is no result and no empty text and no header/footer which is shown on empty result'),
          '#default_value' => $this->getOption('block_hide_empty'),
        ];
        break;

      case 'exposed_form_options':
        $this->view
          ->initHandlers();
        if (!$this->usesExposed() && parent::usesExposed()) {
          $form['exposed_form_options']['warning'] = [
            '#weight' => -10,
            '#markup' => '<div class="messages messages--warning">' . $this->t('Exposed filters in block displays require "Use AJAX" to be set to work correctly.') . '</div>',
          ];
        }
        break;

      case 'allow':
        $form['#title'] .= $this->t('Allow settings in the block configuration');
        $options = [
          'items_per_page' => $this->t('Items per page'),
        ];
        $allow = array_keys(array_filter($this->getOption('allow')));
        $form['allow'] = [
          '#type' => 'checkboxes',
          '#default_value' => $allow,
          '#options' => $options,
        ];
        break;

    }
  }
  
  /**
   * Perform any necessary changes to the form values prior to storage.
   *
   * There is no need for this function to actually store the data.
   */
  public function submitOptionsForm(&$form, FormStateInterface $form_state) {
    parent::submitOptionsForm($form, $form_state);
    $section = $form_state->get('section');
    switch ($section) {
      case 'block_description':
      case 'block_category':
      case 'allow':
      case 'block_hide_empty':
        $this->setOption($section, $form_state->getValue($section));
        break;

    }
  }
  
  /**
   * Adds the configuration form elements specific to this views block plugin.
   *
   * This method allows block instances to override the views items_per_page.
   *
   * @param \Drupal\views\Plugin\Block\ViewsBlock $block
   *   The ViewsBlock plugin.
   * @param array $form
   *   The form definition array for the block configuration form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   *
   * @return array
   *   The renderable form array representing the entire configuration form.
   *
   * @see \Drupal\views\Plugin\Block\ViewsBlock::blockForm()
   */
  public function blockForm(ViewsBlock $block, array &$form, FormStateInterface $form_state) {
    $allow_settings = array_filter($this->getOption('allow'));
    $block_configuration = $block->getConfiguration();
    foreach ($allow_settings as $type => $enabled) {
      if (empty($enabled)) {
        continue;
      }
      switch ($type) {
        case 'items_per_page':
          $form['override']['items_per_page'] = [
            '#type' => 'select',
            '#title' => $this->t('Items per block'),
            '#options' => [
              'none' => $this->t('@count (default setting)', [
                '@count' => $this->getPlugin('pager')
                  ->getItemsPerPage(),
              ]),
              1 => 1,
              2 => 2,
              3 => 3,
              4 => 4,
              5 => 5,
              6 => 6,
              7 => 7,
              8 => 8,
              9 => 9,
              10 => 10,
              12 => 12,
              20 => 20,
              24 => 24,
              40 => 40,
              48 => 48,
            ],
            '#default_value' => $block_configuration['items_per_page'] ?? 'none',
          ];
          break;

      }
    }
    return $form;
  }
  
  /**
   * Handles form validation for the views block configuration form.
   *
   * @param \Drupal\views\Plugin\Block\ViewsBlock $block
   *   The ViewsBlock plugin.
   * @param array $form
   *   The form definition array for the block configuration form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   *
   * @see \Drupal\views\Plugin\Block\ViewsBlock::blockValidate()
   */
  public function blockValidate(ViewsBlock $block, array $form, FormStateInterface $form_state) {
  }
  
  /**
   * Handles form submission for the views block configuration form.
   *
   * @param \Drupal\views\Plugin\Block\ViewsBlock $block
   *   The ViewsBlock plugin.
   * @param array $form
   *   The form definition array for the full block configuration form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   *
   * @see \Drupal\views\Plugin\Block\ViewsBlock::blockSubmit()
   */
  public function blockSubmit(ViewsBlock $block, $form, FormStateInterface $form_state) {
    if ($items_per_page = $form_state->getValue([
      'override',
      'items_per_page',
    ])) {
      $block->setConfigurationValue('items_per_page', $items_per_page === 'none' ? NULL : intval($items_per_page));
    }
    $form_state->unsetValue([
      'override',
      'items_per_page',
    ]);
  }
  
  /**
   * Allows to change the display settings right before executing the block.
   *
   * @param \Drupal\views\Plugin\Block\ViewsBlock $block
   *   The block plugin for views displays.
   */
  public function preBlockBuild(ViewsBlock $block) {
    $config = $block->getConfiguration();
    if (is_numeric($config['items_per_page']) && $config['items_per_page'] > 0) {
      // @todo Delete the intval() in https://www.drupal.org/project/drupal/issues/3521221
      $this->view
        ->setItemsPerPage(intval($config['items_per_page']));
    }
  }
  
  /**
   * {@inheritdoc}
   */
  public function usesExposedFormInBlock() {
    return TRUE;
  }
  
  /**
   * {@inheritdoc}
   */
  public function remove() {
    parent::remove();
    if ($this->entityTypeManager
      ->hasDefinition('block')) {
      $plugin_id = 'views_block:' . $this->view->storage
        ->id() . '-' . $this->display['id'];
      foreach ($this->entityTypeManager
        ->getStorage('block')
        ->loadByProperties([
        'plugin' => $plugin_id,
      ]) as $block) {
        $block->delete();
      }
    }
    if ($this->blockManager instanceof CachedDiscoveryInterface) {
      $this->blockManager
        ->clearCachedDefinitions();
    }
  }

}