/// Thrown for every failed call so the UI can show one consistent error state.
///
/// [code] is the contract's machine-readable key and is the **only** thing
/// callers may branch on. [message] is customer-safe English written by the
/// server and is rendered verbatim — never parsed.
class ApiException implements Exception {
  ApiException(
    this.code, [
    String? message,
    this.status,
    this.requestId,
    String? serverCode,
  ]) : message = message ?? 'Something went wrong',
       serverCode = serverCode ?? code;

  final String code;
  final String message;

  /// Exactly what the server put in `error.code` — `SLOT_CAPACITY_FULL`,
  /// `UNSERVICEABLE_PINCODE`, and so on. [code] is that value translated into
  /// the vocabulary below; this one is kept for the log line and for a support
  /// report, and nothing branches on it.
  final String serverCode;

  /// HTTP status, when there was one. Null for a transport failure.
  final int? status;

  /// The server's `X-Request-Id`, so a support report can be correlated.
  final String? requestId;

  /// The client vocabulary: the contract's codes translated by [normalise],
  /// plus the ones the client raises itself.
  static const String network = 'network';
  static const String invalid = 'invalid';
  static const String invalidName = 'invalid_name';
  static const String invalidOtp = 'invalid_otp';
  static const String unauthorized = 'unauthorized';
  static const String forbidden = 'forbidden';
  static const String notFound = 'not_found';
  static const String conflict = 'conflict';
  static const String unserviceable = 'unserviceable';
  static const String rateLimited = 'rate_limited';
  static const String serverError = 'server_error';

  /// The slot is gone — filled up, or its window passed. Its own code because
  /// the recovery is specific: re-read the slots and go back to picking one.
  static const String slotUnavailable = 'slot_unavailable';

  /// The Miler has already arrived, so the cancel window has closed.
  static const String notCancellable = 'not_cancellable';

  /// Translates the contract's `error.code` into the vocabulary above.
  ///
  /// The wire spells its codes in capitals; the client's are lowercase, and
  /// mapping them is not cosmetic — an untranslated `UNAUTHORIZED` does not
  /// satisfy [isAuthFailure], which is what triggers the token refresh, so a
  /// signed-in customer would have been dropped at the first expired token
  /// instead of silently getting a new one.
  ///
  /// A code that is already lowercase is passed through untouched, and an
  /// unrecognised one falls back to whatever the HTTP status means.
  static String normalise(String raw, String Function() fromStatus) {
    final trimmed = raw.trim();
    if (trimmed.isEmpty) return fromStatus();
    if (trimmed != trimmed.toUpperCase()) return trimmed;
    return switch (trimmed) {
      'UNAUTHORIZED' || 'TOKEN_EXPIRED' => unauthorized,
      'FORBIDDEN' => forbidden,
      'NOT_FOUND' => notFound,
      'INVALID_INPUT' || 'VALIDATION_ERROR' => invalid,
      'SLOT_UNAVAILABLE' || 'SLOT_EXPIRED' || 'SLOT_CAPACITY_FULL' =>
        slotUnavailable,
      'BOOKING_NOT_CANCELLABLE' => notCancellable,
      'UNSERVICEABLE_PINCODE' => unserviceable,
      'RATE_LIMITED' => rateLimited,
      'INTERNAL_ERROR' => serverError,
      _ => fromStatus(),
    };
  }

  /// True when retrying the identical request could plausibly succeed.
  bool get isTransient =>
      code == network || code == serverError || code == rateLimited;

  /// The session is gone; the customer has to sign in again.
  bool get isAuthFailure => code == unauthorized;

  /// The slot the customer picked is no longer bookable — either it filled up
  /// or its window has passed. Both recover the same way: re-fetch the slots
  /// and put them back on slot selection.
  ///
  /// The server distinguishes them (`409 conflict` for a genuine capacity race,
  /// `400 invalid` for a window that has passed) but the customer's next action
  /// is identical, so the client does not.
  bool get needsFreshSlots =>
      code == slotUnavailable ||
      code == conflict ||
      (code == invalid && message.toLowerCase().contains('pickup'));

  @override
  String toString() =>
      'ApiException($code'
      '${serverCode == code ? '' : '/$serverCode'}'
      '${status == null ? '' : ' $status'}): $message'
      '${requestId == null ? '' : ' [req $requestId]'}';
}