/**
 * CSV helpers for the Data explorer export (pure, unit-tested). RFC 4180: fields containing a comma,
 * a double quote, CR or LF are quoted and inner quotes doubled. Attribution rows are prefixed with `#`
 * so spreadsheet users see them and parsers with a comment option can skip them.
 */

export function csvCell(v: unknown): string {
  if (v == null) return '';
  const s = v instanceof Date ? v.toISOString() : String(v);
  return /[",\r\n]/.test(s) ? `"${s.replace(/"/g, '""')}"` : s;
}

export function csvLine(values: readonly unknown[]): string {
  return values.map(csvCell).join(',');
}

/** Comment row: one line, newlines collapsed so the header stays line-oriented. */
export function csvComment(text: string): string {
  return `# ${text.replace(/[\r\n]+/g, ' ').trim()}`;
}

export const EPI_CSV_COLUMNS = [
  'cancer_id',
  'cancer_slug',
  'cancer_name',
  'geography_id',
  'geography_slug',
  'geography_name',
  'iso3',
  'year',
  'year_end',
  'sex',
  'age_group',
  'metric',
  'value',
  'unit',
  'lower_ci',
  'upper_ci',
  'standard_population',
  'estimate_type',
  'site_definition',
  'source_slug',
  'source_name',
  'provenance_id',
  'dataset',
  'dataset_version',
  'source_url',
  'retrieved_at',
] as const;

export type EpiCsvColumn = (typeof EPI_CSV_COLUMNS)[number];

/** File name: cancerindex-epidemiology-<metric>-<geography>-<from>-<to>.csv, safe characters only. */
export function csvFileName(parts: Array<string | number | null | undefined>): string {
  const clean = parts
    .filter((p) => p != null && p !== '')
    .map((p) => String(p).toLowerCase().replace(/[^a-z0-9]+/g, '-').replace(/^-|-$/g, ''))
    .filter(Boolean);
  return `cancerindex-epidemiology-${clean.join('-') || 'export'}.csv`;
}