larkm_integration.module

<?php

/**
 * @file
 * larkm Integration module.
 */

use Drupal\node\NodeInterface;

/**
 * Implements hook_ENTITY_TYPE_presave for Node entities.
 */
function larkm_integration_node_presave(NodeInterface $node) {
  $config = \Drupal::config('larkm_integration.settings');

  $ark_fieldname = $config->get('larkm_integration_ark_fieldname');
  $larkm_hostname = $config->get('larkm_integration_larkm_hostname');
  $naan = $config->get('larkm_integration_naan');
  $shoulder = $config->get('larkm_integration_shoulder');
  $ark_url = $larkm_hostname . '/ark:/' . $naan . '/' . $shoulder . $node->uuid();

  $allowed_bundles = $config->get('larkm_integration_bundles');
  if (in_array($node->bundle(), $allowed_bundles, TRUE) && $node->hasField($ark_fieldname)) {
    $raw_field_values = $node->get($ark_fieldname)->getValue();
    $field_values = [];
    foreach ($raw_field_values as $raw_field_value) {
      $field_values[] = $raw_field_value['value']; 
    }
    if (!in_array($ark_url, $field_values)) {
      $node->{$ark_fieldname}->appendItem($ark_url);
    }
  }
}