/**
 * Add-to-cart refusals the shopper has to be told about.
 *
 * Lives in `core/` and returns a CODE, never a message: `ui/` owns the copy, so
 * each design maps this to its own `productDetail.*` string rather than showing
 * the raw API sentence. Shared by the product page hook and the grid quick-add.
 */
export type AddToCartError = 'CART_FULL' | 'FAILED';

/**
 * The API's stable, machine-readable error code for a failed call, or
 * `undefined` when the failure carried none (a network drop, a timeout, an
 * older backend).
 *
 * Where it comes from: the API answers an error as
 * `{ statusCode, code, message, details?, timestamp, path }`, and the SDK hands
 * that whole body back as `BrainerceError.details`. So the code lives one level
 * in, at `err.details.code` — not on the error itself. Read it rather than the
 * message: the message is human-readable prose that changes freely (and is
 * English regardless of the shopper's language), the code does not.
 */
export function getErrorCode(err: unknown): string | undefined {
  const body = (err as { details?: { code?: unknown } } | null)?.details;
  return typeof body?.code === 'string' ? body.code : undefined;
}

/**
 * A storefront cart holds at most 50 DISTINCT product lines. The 51st add is
 * refused with `400 CART_LINE_LIMIT_REACHED`.
 *
 * The cap applies to storefront traffic only (`storeId` and `vc_*` modes). It
 * does NOT block quantity changes or removals, so "remove something first" is
 * advice the shopper can actually act on.
 *
 * The message match is a FALLBACK, kept only for the window where a storefront
 * built from this template talks to a backend older than the code. Once the
 * backend carrying `CART_LINE_LIMIT_REACHED` is live everywhere, the regex can
 * go: every storefront talks to the current API, so the code is always there.
 * It cannot produce a false `CART_FULL` in the meantime, which is why it costs
 * nothing to keep until then.
 *
 * Anything unrecognised falls through to `FAILED`, which is still a visible
 * message rather than the silence this replaced.
 */
export function toAddToCartError(err: unknown): AddToCartError {
  if (getErrorCode(err) === 'CART_LINE_LIMIT_REACHED') return 'CART_FULL';
  const message = (err as { message?: string } | null)?.message ?? '';
  return /cart can hold at most/i.test(message) ? 'CART_FULL' : 'FAILED';
}