/**
 * Extracts the canonical tournament identity — `(name, year)` — from a scoring
 * event. Used both by the Phase 2 backfill and by the admin create-event flow
 * that auto-provisions a canonical tournament for new qualifying events.
 *
 * Rules:
 *   - If the event name ends with a 4-digit year, strip it; that year wins.
 *   - Otherwise, fall back to the year portion of eventDate (YYYY-MM-DD).
 *   - If neither produces a year, throw.
 */

export interface ScoringEventIdentityInput {
  name: string;
  eventDate: string | Date | null | undefined;
  eventType: string;
}

export interface TournamentIdentity {
  name: string;
  year: number;
}

const YEAR_SUFFIX = /\s+(\d{4})\s*$/;

export function extractTournamentIdentity(ev: ScoringEventIdentityInput): TournamentIdentity {
  const trimmed = ev.name.trim();
  const yearMatch = trimmed.match(YEAR_SUFFIX);
  let cleanName = trimmed;
  let year: number | null = null;

  if (yearMatch) {
    year = parseInt(yearMatch[1], 10);
    cleanName = trimmed.replace(YEAR_SUFFIX, "").trim();
  }

  if (year === null && ev.eventDate !== null && ev.eventDate !== undefined) {
    const iso = ev.eventDate instanceof Date
      ? ev.eventDate.toISOString()
      : String(ev.eventDate);
    year = parseInt(iso.slice(0, 4), 10);
  }

  if (year === null || Number.isNaN(year)) {
    throw new Error(
      `cannot determine year for event "${ev.name}" — no year in name and eventDate is null`,
    );
  }

  return { name: cleanName, year };
}