const STATUS_TITLES = {
  400: 'Ungültige Anfrage',
  401: 'Nicht angemeldet',
  403: 'Zugriff verweigert',
  404: 'Nicht gefunden',
  409: 'Konflikt',
  422: 'Ungültige Daten',
  500: 'Serverfehler',
  502: 'Gateway-Fehler',
  503: 'Dienst nicht erreichbar',
};

const GENERIC_HTTP_TITLES = new Set([
  'not found',
  'unauthorized',
  'forbidden',
  'internal server error',
  'bad request',
  'service unavailable',
]);

/** Normalize any thrown value into a stable backend error object. */
export function backendErrorFrom(err) {
  if (!err) {
    return { message: 'Unbekannter Fehler', status: null, path: null, method: null };
  }
  if (typeof err === 'string') {
    return { message: err, status: null, path: null, method: null };
  }
  if (err.message != null && (err.status != null || err.path != null || err.method != null)) {
    return {
      message: err.message,
      status: err.status ?? null,
      path: err.path ?? null,
      method: err.method ?? null,
    };
  }
  if (err.message != null) {
    return {
      message: err.message,
      status: err.status ?? null,
      path: err.path ?? null,
      method: err.method ?? null,
    };
  }
  return { message: String(err), status: null, path: null, method: null };
}

/** Read structured error from a rejected RTK async thunk action. */
export function resolveBackendError(action) {
  if (action.payload) return backendErrorFrom(action.payload);
  return backendErrorFrom(action.error);
}

export function formatBackendError(error) {
  const normalized = backendErrorFrom(error);
  const { message, status, path, method } = normalized;

  const statusTitle = status != null ? STATUS_TITLES[status] : null;
  const genericTitle =
    message && GENERIC_HTTP_TITLES.has(message.trim().toLowerCase())
      ? statusTitle
      : null;

  const title = statusTitle || genericTitle || (status != null ? `HTTP ${status}` : 'Backend-Fehler');

  const detail =
    message &&
    message.trim().toLowerCase() !== title?.trim().toLowerCase() &&
    !GENERIC_HTTP_TITLES.has(message.trim().toLowerCase())
      ? message
      : null;

  const request = path ? `${method || 'GET'} ${path}` : null;

  return { title, detail, status, request };
}

export function catchBackendError(rejectWithValue) {
  return (err) => rejectWithValue(backendErrorFrom(err));
}

export function isBackendFailure(error) {
  const normalized = backendErrorFrom(error);
  return normalized.status != null || normalized.path != null;
}