/**
 * A name for a passkey the customer did not name themselves (#38).
 *
 * The management screen (#40) lists credentials and offers to revoke them, so
 * two entries that read identically are a screen where the customer cannot tell
 * which device they are removing. A default that says something is the
 * difference between "Passkey, Passkey, Passkey" and a list worth showing.
 *
 * Derived from the authenticator's transports, which is the only thing the
 * ceremony learns about the device. It is a hint rather than a fact — the
 * browser reports what the authenticator claims — so these are deliberately
 * vague. "This device" is honest about a platform authenticator in a way that
 * guessing "MacBook" would not be.
 */

/** The fallback when the authenticator reports nothing usable. */
export const GENERIC_CREDENTIAL_NAME = 'Passkey';

export function defaultCredentialName(transports: readonly string[] | null | undefined): string {
  if (!transports || transports.length === 0) return GENERIC_CREDENTIAL_NAME;

  // Checked in this order because an authenticator can report several. A phone
  // used as a cross-device passkey reports `hybrid` and often `internal` too,
  // and "Phone or tablet" is the more useful of the two readings — `internal`
  // alone means the authenticator built into the machine being used.
  if (transports.includes('hybrid')) return 'Phone or tablet';
  if (transports.includes('internal')) return 'This device';
  if (transports.some((t) => t === 'usb' || t === 'nfc' || t === 'ble')) return 'Security key';

  return GENERIC_CREDENTIAL_NAME;
}

/**
 * The customer's own name for a passkey, or null when they gave none.
 *
 * Trimmed, because a name of spaces is a name nobody can read in a list, and
 * bounded because this is rendered — a customer is naming their laptop, not
 * writing prose, and an unbounded string in a table cell is a layout problem
 * rather than an expressive one.
 */
export const MAX_CREDENTIAL_NAME_LENGTH = 64;

export function readCredentialName(value: unknown): string | null {
  if (typeof value !== 'string') return null;
  const trimmed = value.trim();
  if (trimmed === '') return null;
  return trimmed.slice(0, MAX_CREDENTIAL_NAME_LENGTH);
}