prevent_node_delete-8.x-1.0-alpha3/prevent_node_delete.module

<?php
use \Drupal\Core\Form\FormStateInterface;
use \Drupal\taxonomy\Entity\Term;
use \Drupal\Core\Url;
use Drupal\field\Entity\FieldConfig;
use Drupal\Core\Entity\EntityType;
use Drupal\Core\Routing\RouteMatchInterface;
use \Drupal\views\Views;
use \Drupal\node\Entity\Node;

/**
 * Implements hook_form_alter().
 */
function prevent_node_delete_form_alter(&$form, FormStateInterface $form_state, $form_id) {

  if(strpos($form_id, 'node') !== false && strpos($form_id, 'delete_form') !== false && $form_id != "node_type_delete_form") {
    $map = [];
    $path = \Drupal::request()->getpathInfo();
    $arg  = explode('/',$path);
    $tid = $arg[2];
    $term = Node::load($tid);
    $terms_vocabulary = $term->bundle();
    $ptd_config =  \Drupal::config("prevent_node_delete.settings");
    $vocabularies = array_keys(array_filter($ptd_config->get("bundle")));
    if(in_array($terms_vocabulary, $vocabularies)) {
      $limit = $ptd_config->get("limit");
      $show_button = $ptd_config->get("delete_button");

      $field_map = \Drupal::entityManager()->getFieldMap();

      $entity_reference_fields = [];

      foreach ($field_map as $key => $entity_type) {
        foreach ($entity_type as $field_name => $fields) {
          if($fields["type"] == "entity_reference" && strpos($field_name,"field_") !== false) {
            $entity_reference_fields[$key][$field_name] = $fields;
          }
        }
      }

     foreach ($entity_reference_fields as $entity_type => $field_array) {
       foreach ($field_array as $field_name => $values) {
         foreach($values['bundles'] as $bundle) {
            $field_config = FieldConfig::loadByName($entity_type, $bundle, $field_name);
            if($field_config != null) {
              $field_settings = $field_config->getSettings(); 
              if($field_settings["target_type"] == "node" && $field_settings['handler'] == "default:node"  && isset($field_settings['handler_settings']['target_bundles'])) { 
                 if(in_array($terms_vocabulary, $field_settings['handler_settings']['target_bundles'])) {
                    $map[$entity_type][$field_name] = $field_name;
                  }

              }else if ($field_settings["target_type"] == "node" && $field_settings['handler'] == "views") {
                 $field_settings['handler_settings']['view']['view_name'];
                 $field_settings['handler_settings']['view']['display_name'];
                 $view = Views::getView($field_settings['handler_settings']['view']['view_name']);
                $view->setDisplay($field_settings['handler_settings']['view']['display_name']);
                $displayObj = $view->getDisplay();
                $settings = $displayObj->getOption('filters');
                //print_r($settings); die;
                if(isset($settings)) {
                  foreach ($settings as $key => $stting) {
                    if($stting['entity_type'] == "node"  && in_array($terms_vocabulary, $stting['value'])) {
                    $map[$entity_type][$field_name] = $field_name;
                    }
                  }
                }               
              } 
            }
         } 
       }
     }
        $iterate_limit = $limit;
         $result = [];
         foreach ($map as $entity_type => $fields) {
         $revisionable =  \Drupal::entityTypeManager()->getDefinition($entity_type)->isRevisionable();
          //isRevisionable
         foreach ($fields as $key => $value) {

          if($iterate_limit != 0) {
            if($revisionable) {
              $entities = \Drupal::entityTypeManager()->getStorage($entity_type)->getQuery()
          ->latestRevision()
          ->condition($value, $tid, '=')->range(0,$iterate_limit)->execute();
           }else{
            $entities = \Drupal::entityTypeManager()->getStorage($entity_type)->getQuery()->condition($value, $tid, '=')->range(0,$iterate_limit)->execute();
           }
          }else {
            continue 2;
          }
           if(count($entities) > 0){
            $iterate_limit = $iterate_limit - count($entities); 
            $entity_stack[$entity_type] = $entities;
            $result = $result + $entity_stack;
           } 
         }
        }
          if (count($result) > 0) {
            $markup = t('This node is being used in entities and cannot be deleted. Please remove this node from the following entities first:') . '<ul>';
             foreach ($result as $entity_type => $results) {
               $revisionable =  \Drupal::entityTypeManager()->getDefinition($entity_type)->isRevisionable();

             foreach($results as $id) {
              $entity =  \Drupal::entityTypeManager()->getStorage($entity_type)->load($id);
              $entity_obj = $entity;
              if($revisionable) {
              $revision_ids = \Drupal::entityTypeManager()->getStorage($entity_type)->revisionIds($entity);
              $last_revision_id = end($revision_ids);
              $entity_obj = \Drupal::entityTypeManager()->getStorage($entity_type)->loadRevision($last_revision_id);
              }
              if (!$entity_obj)
                continue;
              $slug = str_replace("_", "/", $entity_type);
              $markup .= '<li>' . \Drupal::l($entity_obj->label(), Url::fromUri('internal:/'.$slug.'/'.$entity_obj->id()), array('attributes' => array('target'=>'_blank'))) . '</li>';
              }
            } 
            if ($iterate_limit == 0)
              $markup .= '<li>' . t("... only the first @limit results are displayed.", array('@limit' => $limit)) . '</li>';
            $markup .= '</ul>';
   
            $form['description']['#markup'] = $markup;
            $form['actions']['submit']['#access'] = $show_button ? TRUE : FALSE;
          }
        
    }
  }
}

/**
 * Implements hook_help().
 */
function prevent_node_delete_help($route_name, RouteMatchInterface $route_match) {
  switch ($route_name) {
    case 'help.page.prevent_node_delete':
      $output = '';
      $output .= '<h3>' . t('About') . '</h3>';
      $output .= '<p>' . t('Prevent Node Delete module is built to prevent the Node deletion when the taxonomy term is associated with entites using entity reference') . '</p>';
      $output .= '<h3>' . t('Uses') . '</h3>';
      $output .= '<dl>';

      $output .= '<dt>' . t('Configuring Prevent Node Delete') . '</dt>';
      $output .= '<dd>' . t('The Prevent Node Delete module provides page for configuring the vocabularies, show delete button, limit, format  <a href=":config">Prevent node Delete settings</a>. Configure vocabularies & test  it by deleting taxomomy term associated with the  entities ', [':config' => \Drupal::url('prevent_node_delete.settings')]) . '</dd>';

      $output .= '</dl>';
      return $output;

    case 'prevent_node_delete.settings':
      return '<p>' . t('This page shows you all available administration tasks for Prevent Node Delete module.') . '</p>';

  }
}