const memoize = <T extends (arg: string) => ReturnType<T>>(fn: T): T => {
  const cache: Record<string, ReturnType<T>> = {};
  return ((arg: string) => {
    if (!(arg in cache)) {
      cache[arg] = fn(arg);
    }
    return cache[arg];
  }) as T;
};

const options = {
  style: "currency" as const,
  currency: "USD",
};
const localeNotAvailable = (1.2).toLocaleString("en", options) !== "$1.20";

const getFallback = (locale: string) =>
  staticFallback[Object.prototype.hasOwnProperty.call(staticFallback, locale) ? locale : "en"];

const staticFallback: Record<string, [string, string]> = {
  en: ["-$1.00", "10,000.2"],
  es: ["-1,00 US$", "10.000,2"],
  fr: ["-1,00 $US", "10 000,2"],
  ja: ["-US$1.00", "10,000.2"],
  ko: ["-US$1.00", "10,000.2"],
  ru: ["-1,00 $", "10 000,2"],
  zh: ["-US$1.00", "10,000.2"],
};

export const prefixFormat = ["sign", "code", "value"] as const;
export const suffixFormat = ["sign", "value", "separator", "code"] as const;
// returns decimal and thousands separator
// FIXME: rename thousands to group
export type GetSeparators = (locale: string) => {
  decimal: string | null | undefined;
  thousands: string | null | undefined;
};
export const getSeparators: GetSeparators = memoize(locale => {
  const res = localeNotAvailable ? getFallback(locale)[1] : (10000.2).toLocaleString(locale);
  let decimal;
  let thousands;

  for (let i = 0; i < res.length; i++) {
    const c = res[i];
    if (/[0-9]/.test(c)) continue;

    if (!thousands) {
      thousands = c;
    } else {
      decimal = c;
    }
  }

  return {
    decimal,
    thousands,
  };
});