type Cell = string | number | null | undefined

/**
 * RFC 4180 CSV. By default starts with a BOM so Excel opens UTF-8 correctly (`bom: false` for machine
 * uploads such as OSHA's ITA). Cells a spreadsheet would treat as a formula are prefixed with an
 * apostrophe (CSV injection).
 */
export function toCsv(header: string[], rows: Cell[][], { bom = true }: { bom?: boolean } = {}): string {
  const cell = (value: Cell) => {
    let text = value === null || value === undefined ? '' : String(value)
    if (/^[=+\-@\t\r]/.test(text)) text = `'${text}`
    return /[",\r\n]/.test(text) ? `"${text.replace(/"/g, '""')}"` : text
  }
  return (bom ? '\uFEFF' : '') + [header, ...rows].map((row) => row.map(cell).join(',')).join('\r\n') + '\r\n'
}