function esc(v: unknown): string {
  if (v === null || v === undefined) return "";
  const s = String(v);
  if (s.includes('"') || s.includes(",") || s.includes("\n") || s.includes(";")) {
    return `"${s.replace(/"/g, '""')}"`;
  }
  return s;
}

export function toCsv(rows: Record<string, unknown>[], columns?: string[]): string {
  if (rows.length === 0) return "";
  const cols = columns ?? Object.keys(rows[0]);
  const head = cols.map(esc).join(",");
  const body = rows.map((r) => cols.map((c) => esc(r[c])).join(",")).join("\n");
  return `${head}\n${body}\n`;
}