$toData = $datum['to']['data'];
$toArray = [];
$tagArray = [];

foreach ($toData as $toUser) {
  array_push($toArray, $toUser['id']);
}

if (isset($datum['message_tags'])) {
  foreach($datum['message_tags'] as $tag) {
    if (array_search($tag['id'], $toArray) !== false) {
      $toArray[$tag['id']] = null;
    }
  }
}
$toArray = array_filter($toArray);

// if $toArray is empty, then this post was a self post, e.g the poster posted on their own wall and tagged a bunch of people
// otherwise the post has a definite recipient
if(!empty($rekeyedToData)) {
  // should never be more than one element in the array
  if(count($rekeyedToData) > 1){
    Logger::log("More than one element in recipient array.");
  }
  $recipient = end($rekeyedToData); // could have used reset, instead of end() to get the first element. Assumption is there would only by one element in the array
}