get_entities_references.php

<?php 

/**
 * Get entities references of EntityDrupalWrapper
 * 
 * For example: we have entity A with ref to B (on field_ref_b) and on entity B we have other ref to C (on field_ref_c)
 * 
 * - Let get all entities B that entity A1 referenced
 *    get_entities_references($w_a, 'field_ref_b');
 * - Let get all entities C that entity A1 referenced
 *    get_entities_references($w_a, 'field_ref_b.field_ref_c');
 * - Unlimit get references "field_ref_b.field_ref_c.field_ref_d.field_ref_e....";
 * 
 * @param \EntityDrupalWrapper $wrapper
 * @param type $refs_str
 * @param type $delimiter
 * @return type
 */
function get_entities_references(\EntityDrupalWrapper $wrapper, $refs_str, $delimiter = '.') {
  $return = array();
  
  //  Split refs_str by delimiter.
  $refs = explode($delimiter, $refs_str);
  
  // No fields.
  if (empty($refs)) {
    return array();
  }
  
  // Last of recursive.
  $count = count($refs);
  if ($count == 1) {
    $ref = reset($refs);
    if ($wrapper->__isset($ref)) {
      $values = $wrapper->{$ref}->value();
      $return = is_array($values) ? $values : array($values);
    }
    return $return;
  }

  // Fetch entities by recursive fields.
  foreach ($refs as $k => $ref) {
    if (count($refs) <= 1) {
      break;
    }
    
    // Marked processed.
    unset($refs[$k]);
    $_refs = $refs;
    
    // Field not exist in wrapper
    if (!$wrapper->__isset($ref)) {
      continue;
    }
    
    // Being process field ref.
    $fwrapper = $wrapper->{$ref};
    if ($fwrapper instanceof \EntityListWrapper) {
      foreach ($fwrapper->getIterator() as $iwrapper) {
        $result = get_entities_references($iwrapper, implode($delimiter, $_refs));
        $return = array_merge($result, $return);
      }
    }
    elseif ($fwrapper instanceof \EntityDrupalWrapper) {
      $result = get_entities_references($fwrapper, implode($delimiter, $_refs));
      $return = array_merge($result, $return);
    }
  }
  return $return;
}