/** Pure helpers for ranking rows (no DB, no server-only) — shared by the cancer Rankings tab and tests. */

export interface ScopedRankingRow {
  metric_slug: string;
  scope_key: string;
}

/** Year encoded in a scope key ("…|year=2021|…"); 0 when absent or "latest". */
export function scopeYear(scopeKey: string): number {
  const m = /year=(\d{4})/.exec(scopeKey);
  return m ? Number(m[1]) : 0;
}

/** Scope key with the year component removed — identifies the (geo, sex, age, level) scope across years. */
export function scopeWithoutYear(scopeKey: string): string {
  return scopeKey
    .split('|')
    .filter((part) => !part.startsWith('year='))
    .join('|');
}

/**
 * Keep one row per (metric, scope-without-year): the latest year. Earlier yearly snapshots are
 * left to the ranking pages. Input order is preserved for the surviving rows; ties on year keep
 * the first row seen.
 */
export function latestYearPerScope<T extends ScopedRankingRow>(rows: T[]): { rows: T[]; hidden: number } {
  const latest = new Map<string, { row: T; year: number; index: number }>();
  rows.forEach((r, index) => {
    const key = `${r.metric_slug}|${scopeWithoutYear(r.scope_key)}`;
    const year = scopeYear(r.scope_key);
    const cur = latest.get(key);
    if (!cur || year > cur.year) latest.set(key, { row: r, year, index: cur?.index ?? index });
  });
  const kept = [...latest.values()].sort((a, b) => a.index - b.index).map((x) => x.row);
  return { rows: kept, hidden: rows.length - kept.length };
}