/**
 * Tiny CSV serializer. RFC 4180 — quotes fields that contain commas, quotes, or newlines.
 */
export function csvEscape(value: unknown): string {
	if (value === null || value === undefined) return '';
	const s = String(value);
	if (/[",\n\r]/.test(s)) {
		return `"${s.replace(/"/g, '""')}"`;
	}
	return s;
}

export function csvRow(values: unknown[]): string {
	return values.map(csvEscape).join(',');
}

export function csvBuild(rows: unknown[][]): string {
	return rows.map(csvRow).join('\r\n');
}

/** Build a Response with a CSV download. */
export function csvResponse(csv: string, filename: string): Response {
	// Prepend BOM so Excel detects UTF-8 (important for Thai characters)
	const body = '\uFEFF' + csv;
	return new Response(body, {
		headers: {
			'Content-Type': 'text/csv; charset=utf-8',
			'Content-Disposition': `attachment; filename="${filename}"`
		}
	});
}