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src/utils/backendError.js

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+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;
+}