import 'server-only';
import { fmtMoney } from '@/lib/format';
import { getDisplayCurrency } from '@/lib/auth/session';
import { latestRate } from './fx';

export interface Display {
  currency: string;
  rate: number;
  /** true when the requested currency had no FX rate and USD is shown instead */
  fallback: boolean;
  money: (usd: number | null | undefined, opts?: { compact?: boolean; digits?: number }) => string;
}

/** Resolve the member's display currency and a formatter converting USD values at the latest rate. */
export async function getDisplay(): Promise<Display> {
  const currency = await getDisplayCurrency();
  const rate = await latestRate(currency);
  const effective = rate ? currency : 'USD';
  const r = rate ?? 1;
  return {
    currency: effective,
    rate: r,
    fallback: !rate && currency !== 'USD',
    money: (usd, opts) => (usd === null || usd === undefined ? '—' : fmtMoney(usd * r, effective, opts)),
  };
}