block_button_modal.module

<?php

/**
 * @file
 * Block button modal module file.
 */

use Drupal\Core\Form\FormStateInterface;

/**
 * Implements hook_form_BASE_FORM_ID_alter().
 */
function block_button_modal_form_block_form_alter(&$form, FormStateInterface $form_state, $form_id) {
  /**
   * @var \Drupal\block\BlockInterface $block
   */
  $block = $form_state->getBuildInfo()['callback_object']->getEntity();

  $form['third_party_settings']['block_button_modal']['enabled'] = [
    '#type' => 'checkbox',
    '#title' => t('Show block as modal dialog'),
    '#description' => t('Show a button instead of the actual block. When the button is clicked, the block will show in a modal dialog.'),
    '#default_value' => $block->getThirdPartySetting('block_button_modal', 'enabled', FALSE),
  ];

}

/**
 * Implements hook_ENTITY_TYPE_view_alter().
 */
function block_button_modal_block_view_alter(array &$build, $entity, $display) {
  echo "block_button_modal checkpoint 1<br>\n";
    if (!isset($build['#configuration']['third_party_settings']['block_button_modal']) || !$build['#configuration']['third_party_settings']['block_button_modal']['enabled']) {
    return;
  }
  echo "block_button_modal checkpoint 2<br>\n";
  $build['#theme'] = 'block_button_modal_block';
  $build['#block_label'] = $build['#configuration']['label'];
}

/**
 * Implements hook_theme().
 */
function block_button_modal_theme($existing, $type, $theme, $path) {
  return [
    'block_button_modal_block' => [
      'render element' => 'elements',
    ],
  ];
}

/**
 * Implements hook_preprocess_HOOK().
 */
function template_preprocess_block_button_modal_block(&$variables) {
  echo "block_button_modal checkpoint 3<br>\n";
  template_preprocess_block($variables);
  $variables['block_button_modal_block_id'] = str_replace('_', '-', 'block_button_modal_block_' . $variables['elements']['#id']);
  $variables['block_label'] = $variables['elements']['#block_label'];
  $variables['#attached']['library'][] = 'block_button_modal/block_button_modal_block';

  $variables['block_button_modal_button'] = [
    '#type' => 'button',
    '#button_type' => 'block_button_modal',
    '#value' => $variables['elements']['#block_label'],
    '#block_button_modal_block_id' => $variables['block_button_modal_block_id'],
    '#attributes' => [
      'type' => 'button',
      'data-block-button-modal-title' => $variables['elements']['#block_label'],
    ],
  ];
}

/**
 * Implements hook_theme_suggestions_HOOK_alter().
 */
function block_button_modal_theme_suggestions_block_button_modal_block_alter(array &$suggestions, array $variables) {
  $suggestions[] = 'block_button_modal_block__' . $variables['elements']['#id'];
}

/**
 * Implements hook_theme_suggestions_HOOK_alter().
 */
function block_button_modal_theme_suggestions_input_alter(array &$suggestions, array $variables) {
  if (isset($variables['element']['#button_type']) && $variables['element']['#button_type'] === 'block_button_modal') {
    $suggestions[] = 'input__block_button_modal';
    $suggestions[] = 'input__' . $variables['element']['#block_button_modal_block_id'];
  }
}