// Pure price-mode logic (no DOM), imported by both the element and its test.

/** Which of the two prices the tier radios should carry. */
export type PriceMode = 'founder' | 'list';

/** The two prices a tier card publishes as data attributes. */
export interface TierPrices {
  std: string | null;
  founder: string | null;
}

/**
 * The price a tier should carry in the given mode.
 *
 * Returns `null` when the card does not publish the price that mode needs, so
 * the caller leaves the DOM alone rather than writing `undefined` into a form
 * value the server computes on. That happens on a page rendered with the
 * founder window shut, where there is no toggle and nothing should move.
 */
export function priceFor(prices: TierPrices, mode: PriceMode): string | null {
  const chosen = mode === 'founder' ? prices.founder : prices.std;
  return chosen === null || chosen === '' ? null : chosen;
}

/**
 * Render a monthly price the way the tier card writes it.
 *
 * Kept here rather than inlined so the test pins the format: the server
 * renders the first one, the toggle renders every one after, and the two must
 * agree or the price visibly reformats the first time somebody flips it.
 */
export function formatMonthly(price: string): string {
  return `$${price}/mo`;
}