export function getCountryName(iso: string, locale = "en"): string {
  try {
    const dn = new Intl.DisplayNames([locale], { type: "region" });
    return dn.of(iso.toUpperCase()) ?? iso;
  } catch {
    return iso;
  }
}

export function formatPrice(cents: number, currency = "EUR", locale = "en"): string {
  try {
    return new Intl.NumberFormat(locale, {
      style: "currency",
      currency,
      minimumFractionDigits: 2,
    }).format(cents / 100);
  } catch {
    return `${currency} ${(cents / 100).toFixed(2)}`;
  }
}

/**
 * A plan's data allowance as a shopper reads it.
 *
 * Zero is not "0 GB" — an unmetered plan is the thing the customer is being
 * sold, and printing a zero next to a price reads as a broken row.
 */
export function formatDataAllowance(dataGb: number): string {
  if (!Number.isFinite(dataGb) || dataGb <= 0) return "Unlimited data";
  if (dataGb < 1) return `${Math.round(dataGb * 1024)} MB data`;
  return `${Number.isInteger(dataGb) ? dataGb : dataGb.toFixed(1)} GB data`;
}

/** A plan's validity window, singular-aware. */
export function formatValidity(validityDays: number): string {
  if (!Number.isFinite(validityDays) || validityDays <= 0) return "No expiry";
  if (validityDays === 1) return "1 day";
  if (validityDays % 7 === 0 && validityDays >= 7) {
    const weeks = validityDays / 7;
    return weeks === 1 ? "1 week" : `${weeks} weeks`;
  }
  return `${validityDays} days`;
}

/**
 * Bytes as a usage meter shows them.
 *
 * Decimal units (1 GB = 1000 MB), because that is the unit a data bundle is
 * sold in — showing 0.93 GB left of a 1 GB plan the moment it is bought is a
 * support ticket, not a rounding preference.
 */
export function formatBytes(bytes: number): string {
  if (!Number.isFinite(bytes) || bytes <= 0) return "0 MB";
  if (bytes >= 1_000_000_000) return `${(bytes / 1_000_000_000).toFixed(bytes >= 10_000_000_000 ? 0 : 1)} GB`;
  if (bytes >= 1_000_000) return `${Math.round(bytes / 1_000_000)} MB`;
  return `${Math.max(1, Math.round(bytes / 1_000))} KB`;
}

/** Days left until an ISO timestamp, floored at zero. Null when unparseable. */
export function daysUntil(iso: string | undefined, now: Date = new Date()): number | null {
  if (!iso) return null;
  const then = Date.parse(iso);
  if (Number.isNaN(then)) return null;
  return Math.max(0, Math.ceil((then - now.getTime()) / 86_400_000));
}

export type DisplayCurrency = "EUR" | "USD" | "GBP";

export const SUPPORTED_CURRENCIES: DisplayCurrency[] = ["EUR", "USD", "GBP"];

export function getDisplayCurrency(countryIso: string): DisplayCurrency {
  const map: Record<string, DisplayCurrency> = {
    US: "USD",
    GB: "GBP",
  };
  return map[countryIso.toUpperCase()] ?? "EUR";
}