download CSV

header('Content-Type: text/csv; charset=utf-8');
header('Content-Disposition: attachment; filename=data.csv');
header('Pragma: no-cache');

$output = fopen('php://output', 'w');

fputcsv($output, $this->table_header);

foreach ($report_data as $key => $value) {
  fputcsv($output, implode(',', $value));
}

fclose($output);