survey_manager.module

<?php

/**
 * @file
 * Contains survey_manager.module.
 */

use Drupal\block\Entity\Block;
use Drupal\Core\Routing\RouteMatchInterface;
use Drupal\Core\Form\FormStateInterface;
use Symfony\Component\HttpFoundation\RedirectResponse;

/**
 * Implements hook_help().
 */
function survey_manager_help($route_name, RouteMatchInterface $route_match) {
  if ($route_name === 'help.page.survey_manager') {
    $output = '<p>' . t('Manage third-party surveys.') . '</p>';
    return $output;
  }
}

/**
 * Implements hook_page_bottom().
 */
function survey_manager_page_bottom(array &$page_bottom) {
  // Get embedable suryves.
  $surveys = _survey_manager_get_surveys('survey-embed');
  foreach ($surveys as $block) {
    // Check this answer http://drupal.stackexchange.com/a/185691/23477.
    if ($block->access('view')) {
      $page_bottom['survey_manager'][] = [
        '#markup' => $block->get('settings')['embed_code'],
        '#allowed_tags' => ['script'],
      ];
    }
  }
}

/**
 * Get list of survey blocks by type.
 *
 * @return array
 *   Array of survey blocks.
 */
function _survey_manager_get_surveys($survey_plugin_id) {
  $query = \Drupal::entityQuery('block')->condition('plugin', $survey_plugin_id);
  return Block::loadMultiple($query->execute());
}

/**
 * Implements hook_form_alter().
 */
function survey_manager_form_alter(&$form, FormStateInterface $form_state, $form_id) {
  switch ($form_id) {
    case 'block_form':
      if ($form['settings']['#attributes']['class'][0] == 'block-survey-form') {
        $form['actions']['submit']['#submit'][] = 'survey_manager_block_submit_callback';
      }
      break;

    case 'block_admin_display_form':
      foreach ($form['blocks'] as $key => $block) {
        if (!empty($block['operations']['#links']['edit']['url'])) {
          $block_plugin_id = $block['operations']['#links']['edit']['url']->getOptions()['entity']->getPluginId();
          if ($block_plugin_id == 'survey_embed_code_block') {
            unset($form['blocks'][$key]);
          }
        }
      }
      break;
  }
}

/**
 * Custom block submit callback.
 *
 * @return \Symfony\Component\HttpFoundation\RedirectResponse
 *   Redirects to the survey list page.
 */
function survey_manager_block_submit_callback() {
  $response = new RedirectResponse(\Drupal::url('survey_manager.survey_list_controller_index'));
  return $response->send();
}