code: private function fetchData(FileUpload $uploader, string $separator, callable $callback): array
      {
          $data = [];
          $files = $this->getFiles($uploader);
          $delimiter = $this->getDelimiter($separator);
  
          foreach ($files as $file) {
              $fp = fopen($file, 'r');
  
              while (false !== ($row = fgetcsv($fp, 0, $delimiter))) {
                  $data = $callback($data, $row);
              }
          }
  
          return $data;
      }
docs: Returns an array of data from the imported CSV files.
  
  @return string[]