// Pure helpers shared by server and client components. Must not be "use client",
// or server pages calling these get a client reference instead of the function.

// sessionId: one session of a "pick sessions" option (those are waited for per session).
export type WaitlistLine = { eventOptionId: string; variantId?: string | null; sessionId?: string | null; label: string };

/** "Drop-in (Adult)" or "Drop-in — Class 2, Wed 4 Nov" for a waitlist entry. */
export function entryLineName(e: { eventOption: { name: string }; variant?: { name: string } | null; session?: { label?: string | null; startsAt: string } | null }): string {
  const base = `${e.eventOption.name}${e.variant ? ` (${e.variant.name})` : ""}`;
  if (!e.session) return base;
  const when = new Date(e.session.startsAt).toLocaleDateString(undefined, { weekday: "short", day: "numeric", month: "short" });
  return `${base} — ${e.session.label ? `${e.session.label}, ` : ""}${when}`;
}

/** The sold-out lines of an event, for the waitlist button. */
export function soldOutLines(options: { id: string; name: string; stockLimit?: number; availableCount?: number | null; variants?: { id: string; name: string; stockLimit?: number; availableCount?: number | null }[] | null }[]): WaitlistLine[] {
  const out: WaitlistLine[] = [];
  for (const o of options || []) {
    const optOut = (o.stockLimit ?? 0) > 0 && o.availableCount !== undefined && o.availableCount !== null && o.availableCount <= 0;
    const variants = o.variants || [];
    if (variants.length > 0) {
      for (const v of variants) {
        const vOut = (v.stockLimit ?? 0) > 0 && v.availableCount !== undefined && v.availableCount !== null && v.availableCount <= 0;
        if (optOut || vOut) out.push({ eventOptionId: o.id, variantId: v.id, label: `${o.name} (${v.name})` });
      }
    } else if (optOut) {
      out.push({ eventOptionId: o.id, label: o.name });
    }
  }
  return out;
}