class Attachment

class Attachment extends DisplayPluginBase {
  
  /**
   * Whether the display allows the use of a pager or not.
   *
   * @var bool
   */
  protected $usesPager = FALSE;
  
  /**
   * {@inheritdoc}
   */
  protected function defineOptions() {
    $options = parent::defineOptions();
    $options['displays'] = [
      'default' => [],
    ];
    $options['attachment_position'] = [
      'default' => 'before',
    ];
    $options['inherit_arguments'] = [
      'default' => TRUE,
    ];
    $options['inherit_exposed_filters'] = [
      'default' => FALSE,
    ];
    $options['inherit_pager'] = [
      'default' => FALSE,
    ];
    $options['render_pager'] = [
      'default' => FALSE,
    ];
    return $options;
  }
  
  /**
   * {@inheritdoc}
   */
  public function execute() {
    return $this->view
      ->render($this->display['id']);
  }
  
  /**
   * Gets the positions for the attachment in relation to the parent display.
   */
  public function attachmentPositions($position = NULL) {
    $positions = [
      'before' => $this->t('Before'),
      'after' => $this->t('After'),
      'both' => $this->t('Both'),
    ];
    if ($position) {
      return $positions[$position];
    }
    return $positions;
  }
  
  /**
   * Provide the summary for attachment options in the views UI.
   *
   * This output is returned as an array.
   */
  public function optionsSummary(&$categories, &$options) {
    // It is very important to call the parent function here:
    parent::optionsSummary($categories, $options);
    $categories['attachment'] = [
      'title' => $this->t('Attachment settings'),
      'column' => 'second',
      'build' => [
        '#weight' => -10,
      ],
    ];
    $displays = array_filter($this->getOption('displays'));
    if (count($displays) > 1) {
      $attach_to = $this->t('Multiple displays');
    }
    elseif (count($displays) == 1) {
      $display = array_shift($displays);
      if ($display = $this->view->storage
        ->getDisplay($display)) {
        $attach_to = $display['display_title'];
      }
    }
    if (!isset($attach_to)) {
      $attach_to = $this->t('Not defined');
    }
    $options['displays'] = [
      'category' => 'attachment',
      'title' => $this->t('Attach to'),
      'value' => $attach_to,
    ];
    $options['attachment_position'] = [
      'category' => 'attachment',
      'title' => $this->t('Attachment position'),
      'value' => $this->attachmentPositions($this->getOption('attachment_position')),
    ];
    $options['inherit_arguments'] = [
      'category' => 'attachment',
      'title' => $this->t('Inherit contextual filters'),
      'value' => $this->getOption('inherit_arguments') ? $this->t('Yes') : $this->t('No'),
    ];
    $options['inherit_exposed_filters'] = [
      'category' => 'attachment',
      'title' => $this->t('Inherit exposed filters'),
      'value' => $this->getOption('inherit_exposed_filters') ? $this->t('Yes') : $this->t('No'),
    ];
    $options['inherit_pager'] = [
      'category' => 'pager',
      'title' => $this->t('Inherit pager'),
      'value' => $this->getOption('inherit_pager') ? $this->t('Yes') : $this->t('No'),
    ];
    $options['render_pager'] = [
      'category' => 'pager',
      'title' => $this->t('Render pager'),
      'value' => $this->getOption('render_pager') ? $this->t('Yes') : $this->t('No'),
    ];
  }
  
  /**
   * Provide the default form for setting options.
   */
  public function buildOptionsForm(&$form, FormStateInterface $form_state) {
    // It is very important to call the parent function here:
    parent::buildOptionsForm($form, $form_state);
    switch ($form_state->get('section')) {
      case 'inherit_arguments':
        $form['#title'] .= $this->t('Inherit contextual filters');
        $form['inherit_arguments'] = [
          '#type' => 'checkbox',
          '#title' => $this->t('Inherit'),
          '#description' => $this->t('Should this display inherit its contextual filter values from the parent display to which it is attached?'),
          '#default_value' => $this->getOption('inherit_arguments'),
        ];
        break;

      case 'inherit_exposed_filters':
        $form['#title'] .= $this->t('Inherit exposed filters');
        $form['inherit_exposed_filters'] = [
          '#type' => 'checkbox',
          '#title' => $this->t('Inherit'),
          '#description' => $this->t('Should this display inherit its exposed filter values from the parent display to which it is attached?'),
          '#default_value' => $this->getOption('inherit_exposed_filters'),
        ];
        break;

      case 'inherit_pager':
        $form['#title'] .= $this->t('Inherit pager');
        $form['inherit_pager'] = [
          '#type' => 'checkbox',
          '#title' => $this->t('Inherit'),
          '#description' => $this->t('Should this display inherit its paging values from the parent display to which it is attached?'),
          '#default_value' => $this->getOption('inherit_pager'),
        ];
        break;

      case 'render_pager':
        $form['#title'] .= $this->t('Render pager');
        $form['render_pager'] = [
          '#type' => 'checkbox',
          '#title' => $this->t('Render'),
          '#description' => $this->t('Should this display render the pager values? This is only meaningful if inheriting a pager.'),
          '#default_value' => $this->getOption('render_pager'),
        ];
        break;

      case 'attachment_position':
        $form['#title'] .= $this->t('Position');
        $form['attachment_position'] = [
          '#title' => $this->t('Position'),
          '#type' => 'radios',
          '#description' => $this->t('Attach before or after the parent display?'),
          '#options' => $this->attachmentPositions(),
          '#default_value' => $this->getOption('attachment_position'),
        ];
        break;

      case 'displays':
        $form['#title'] .= $this->t('Attach to');
        $displays = [];
        foreach ($this->view->storage
          ->get('display') as $display_id => $display) {
          if ($this->view->displayHandlers
            ->has($display_id) && $this->view->displayHandlers
            ->get($display_id)
            ->acceptAttachments()) {
            $displays[$display_id] = $display['display_title'];
          }
        }
        $form['displays'] = [
          '#title' => $this->t('Displays'),
          '#type' => 'checkboxes',
          '#description' => $this->t('Select which display or displays this should attach to.'),
          '#options' => array_map('\\Drupal\\Component\\Utility\\Html::escape', $displays),
          '#default_value' => $this->getOption('displays'),
        ];
        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 $form_state) {
    // It is very important to call the parent function here:
    parent::submitOptionsForm($form, $form_state);
    $section = $form_state->get('section');
    switch ($section) {
      case 'displays':
        $form_state->setValue($section, array_filter($form_state->getValue($section)));
      case 'inherit_arguments':
      case 'inherit_pager':
      case 'render_pager':
      case 'inherit_exposed_filters':
      case 'attachment_position':
        $this->setOption($section, $form_state->getValue($section));
        break;

    }
  }
  
  /**
   * {@inheritdoc}
   */
  public function attachTo(ViewExecutable $view, $display_id, array &$build) {
    $displays = $this->getOption('displays');
    if (empty($displays[$display_id])) {
      return;
    }
    if (!$this->access()) {
      return;
    }
    $args = $this->getOption('inherit_arguments') ? $this->view->args : [];
    $view->setArguments($args);
    $view->setDisplay($this->display['id']);
    if ($this->getOption('inherit_pager')) {
      $view->display_handler->usesPager = $this->view->displayHandlers
        ->get($display_id)
        ->usesPager();
      $view->display_handler
        ->setOption('pager', $this->view->displayHandlers
        ->get($display_id)
        ->getOption('pager'));
    }
    $attachment = $view->buildRenderable($this->display['id'], $args);
    switch ($this->getOption('attachment_position')) {
      case 'before':
        $this->view->attachment_before[] = $attachment;
        break;

      case 'after':
        $this->view->attachment_after[] = $attachment;
        break;

      case 'both':
        $this->view->attachment_before[] = $attachment;
        $this->view->attachment_after[] = $attachment;
        break;

    }
  }
  
  /**
   * {@inheritdoc}
   */
  public function usesExposed() {
    // Attachment displays only use exposed widgets if they are set to inherit
    // the exposed filter settings of their parent display.
    if (!empty($this->options['inherit_exposed_filters']) && parent::usesExposed()) {
      return TRUE;
    }
    return FALSE;
  }
  
  /**
   * {@inheritdoc}
   */
  public function displaysExposed() {
    // If an attachment is set to inherit the exposed filter settings from its
    // parent display, then don't render and display a second set of exposed
    // filter widgets.
    return $this->options['inherit_exposed_filters'] ? FALSE : TRUE;
  }
  
  /**
   * {@inheritdoc}
   */
  public function renderPager() {
    return $this->usesPager() && $this->getOption('render_pager');
  }

}