Checksum comparison from mobile to API endpoint

checksum.md

function _x($data) {
  // Store the hash data from mobile.
  $hash_from_mobile = end($data);

  // Remove the hash data as it is not needed anymore.
  array_pop($data);
  // Serialize the data before in order to calculate the checksum value.
  $query_string = serialize($data);
  $hash = md5($query_string);

  // Compare the checksum result to the hash value from mobile.
  // If true this means the sync is completed successfully.
  if ($hash_from_mobile == $hash) {
    $sync_status = 'Completed';

    // Check if the item ID exist on the database.
    if (id_exist) {
      // Update the record.
    }
    else {
      // Record the item.
      foreach ($data => $item) {
        // Do the math here.
      }
    }

    return drupal_json_output($sync_status);
  }
  // This means that the sync has failed or terminated somewhere before the data
  // has been transfered to the receiving endpoint.
  else {
    $sync_status = 'Failed';
    return $sync_status;
  }
}