/**
 * Czech National Bank (ČNB) exchange rate service.
 * Fetches daily rates and caches them.
 * API: https://api.cnb.cz/cnbapi/exrates/daily
 */

interface CnbRate {
  currencyCode: string;
  rate: number;
  amount: number;
}

const rateCache: Record<string, Record<string, number>> = {};

async function fetchRatesForDate(
  date?: string,
): Promise<Record<string, number>> {
  const key = date || "today";
  if (rateCache[key]) return rateCache[key];

  try {
    let url = "https://api.cnb.cz/cnbapi/exrates/daily?lang=EN";
    if (date) url += `&date=${date}`;

    const response = await fetch(url);
    if (!response.ok) throw new Error(`CNB API: ${response.status}`);

    const data = (await response.json()) as { rates: CnbRate[] };
    const rates: Record<string, number> = { CZK: 1 };

    for (const r of data.rates) {
      rates[r.currencyCode] = r.rate / r.amount;
    }

    rateCache[key] = rates;
    return rates;
  } catch (err) {
    console.error("Failed to fetch CNB exchange rates:", err);
    if (rateCache["today"]) return rateCache["today"];
    return { CZK: 1, EUR: 25, USD: 22, GBP: 28 };
  }
}

/** Convert an amount from a given currency to CZK using CNB rates */
export async function toCzk(
  amount: number,
  currency: string,
  date?: string,
): Promise<number> {
  if (currency === "CZK") return amount;
  const rates = await fetchRatesForDate(date);
  const rate = rates[currency];
  if (!rate) return amount;
  return Math.round(amount * rate * 100) / 100;
}

/** Get CNB rate for a currency (CZK per 1 unit), optionally for a specific date */
export async function getRate(
  currency: string,
  date?: string,
): Promise<number> {
  if (currency === "CZK") return 1;
  const rates = await fetchRatesForDate(date);
  return rates[currency] || 1;
}