/**
 * Toolkit - Currency Formatting
 *
 * Our product currently operates in Japanese Yen only, but we keep a single
 * helper so the portal and BFF share the same formatting behaviour.
 *
 * The function still accepts legacy signatures (`formatCurrency(amount, "JPY", "¥")`)
 * so existing call sites remain compatible.
 */

export type SupportedCurrency = "JPY";

type LegacyOptions = {
  /**
   * Optional locale override. Defaults to "ja-JP".
   */
  locale?: string | undefined;
  /**
   * Set to false if you ever want to hide the symbol. Defaults to true.
   */
  showSymbol?: boolean | undefined;
  /**
   * Optional custom symbol. Defaults to "¥".
   */
  currencySymbol?: string | undefined;
};

const DEFAULT_CURRENCY: SupportedCurrency = "JPY";
const DEFAULT_SYMBOL = "¥";
const DEFAULT_LOCALE = "ja-JP";

export const getCurrencyLocale = (_currency?: string): string => DEFAULT_LOCALE;

const normalizeOptions = (
  currencyOrOptions?: string | LegacyOptions,
  symbolOrOptions?: string | LegacyOptions
) => {
  const result: {
    currency: string;
    symbol: string;
    locale: string;
    showSymbol: boolean;
  } = {
    currency: DEFAULT_CURRENCY,
    symbol: DEFAULT_SYMBOL,
    locale: DEFAULT_LOCALE,
    showSymbol: true,
  };

  const applyOptions = (opts?: LegacyOptions) => {
    if (!opts) return;
    if (opts.locale) result.locale = opts.locale;
    if (typeof opts.showSymbol === "boolean") result.showSymbol = opts.showSymbol;
    if (opts.currencySymbol) result.symbol = opts.currencySymbol;
  };

  if (typeof currencyOrOptions === "string") {
    result.currency = currencyOrOptions;
  } else {
    applyOptions(currencyOrOptions);
  }

  if (typeof symbolOrOptions === "string") {
    result.symbol = symbolOrOptions;
  } else {
    applyOptions(symbolOrOptions);
  }

  // Even if a different currency code is provided, we treat it like JPY for now.
  const fractionDigits = result.currency.toUpperCase() === "JPY" ? 0 : 2;

  return { ...result, fractionDigits };
};

export function formatCurrency(
  amount: number,
  currencyOrOptions?: string | LegacyOptions,
  symbolOrOptions?: string | LegacyOptions
): string {
  const { locale, symbol, showSymbol, fractionDigits } = normalizeOptions(
    currencyOrOptions,
    symbolOrOptions
  );

  const formatted = amount.toLocaleString(locale, {
    minimumFractionDigits: fractionDigits,
    maximumFractionDigits: fractionDigits,
  });

  return showSymbol ? `${symbol}${formatted}` : formatted;
}

export function parseCurrency(value: string): number | null {
  const cleaned = value.replace(/[¥$€,\s]/g, "");
  const parsed = Number.parseFloat(cleaned);
  return Number.isFinite(parsed) ? parsed : null;
}