// Simple CSV export — opens directly in Excel. Includes UTF-8 BOM for Bangla.
export function downloadCSV(filename: string, rows: (string | number)[][]) {
  const esc = (v: string | number) => {
    const s = String(v ?? "");
    return /[",\n]/.test(s) ? `"${s.replace(/"/g, '""')}"` : s;
  };
  const csv = "\uFEFF" + rows.map((r) => r.map(esc).join(",")).join("\n");
  const blob = new Blob([csv], { type: "text/csv;charset=utf-8;" });
  const url = URL.createObjectURL(blob);
  const a = document.createElement("a");
  a.href = url;
  a.download = filename.endsWith(".csv") ? filename : `${filename}.csv`;
  document.body.appendChild(a);
  a.click();
  a.remove();
  URL.revokeObjectURL(url);
}