From 8f513495e33942453d6b4e3aec5517e4fb8a01cd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=B6rg=20Lohrer?= <info.empeiria@gmail.com>
Date: Tue, 21 Apr 2026 13:32:34 +0200
Subject: [PATCH] feat(app): activeLocale-store mit persistence +
 initial-detection

---
 app/src/lib/i18n/activeLocale.test.ts | 65 +++++++++++++++++++++++++++
 app/src/lib/i18n/activeLocale.ts      | 61 +++++++++++++++++++++++++
 2 files changed, 126 insertions(+)
 create mode 100644 app/src/lib/i18n/activeLocale.test.ts
 create mode 100644 app/src/lib/i18n/activeLocale.ts

diff --git a/app/src/lib/i18n/activeLocale.test.ts b/app/src/lib/i18n/activeLocale.test.ts
new file mode 100644
index 0000000..300d73f
--- /dev/null
+++ b/app/src/lib/i18n/activeLocale.test.ts
@@ -0,0 +1,65 @@
+import { describe, it, expect, beforeEach } from 'vitest';
+import { detectInitialLocale } from './activeLocale';
+
+describe('detectInitialLocale', () => {
+  beforeEach(() => {
+    globalThis.localStorage?.clear?.();
+  });
+
+  it('nimmt wert aus localStorage, wenn vorhanden und gültig', () => {
+    const storage = new Map<string, string>([['locale', 'en']]);
+    expect(detectInitialLocale({
+      storage: {
+        getItem: (k) => storage.get(k) ?? null,
+        setItem: () => {}
+      },
+      navigatorLanguage: 'de-DE',
+      supported: ['de', 'en']
+    })).toBe('en');
+  });
+
+  it('fällt auf navigator.language zurück, wenn storage leer', () => {
+    expect(detectInitialLocale({
+      storage: {
+        getItem: () => null,
+        setItem: () => {}
+      },
+      navigatorLanguage: 'en-US',
+      supported: ['de', 'en']
+    })).toBe('en');
+  });
+
+  it('normalisiert navigator.language (de-AT → de)', () => {
+    expect(detectInitialLocale({
+      storage: {
+        getItem: () => null,
+        setItem: () => {}
+      },
+      navigatorLanguage: 'de-AT',
+      supported: ['de', 'en']
+    })).toBe('de');
+  });
+
+  it('fällt auf ersten supported eintrag, wenn navigator unbekannt', () => {
+    expect(detectInitialLocale({
+      storage: {
+        getItem: () => null,
+        setItem: () => {}
+      },
+      navigatorLanguage: 'fr-FR',
+      supported: ['de', 'en']
+    })).toBe('de');
+  });
+
+  it('ignoriert ungültige werte im storage', () => {
+    const storage = new Map<string, string>([['locale', 'fr']]);
+    expect(detectInitialLocale({
+      storage: {
+        getItem: (k) => storage.get(k) ?? null,
+        setItem: () => {}
+      },
+      navigatorLanguage: 'en-US',
+      supported: ['de', 'en']
+    })).toBe('en');
+  });
+});
diff --git a/app/src/lib/i18n/activeLocale.ts b/app/src/lib/i18n/activeLocale.ts
new file mode 100644
index 0000000..611be98
--- /dev/null
+++ b/app/src/lib/i18n/activeLocale.ts
@@ -0,0 +1,61 @@
+import { writable, type Writable } from 'svelte/store';
+
+export type SupportedLocale = 'de' | 'en';
+export const SUPPORTED_LOCALES: readonly SupportedLocale[] = ['de', 'en'] as const;
+const STORAGE_KEY = 'locale';
+
+interface Storage {
+  getItem: (key: string) => string | null;
+  setItem: (key: string, value: string) => void;
+}
+
+export interface DetectArgs {
+  storage: Storage;
+  navigatorLanguage: string | undefined;
+  supported: readonly string[];
+}
+
+export function detectInitialLocale(args: DetectArgs): SupportedLocale {
+  const stored = args.storage.getItem(STORAGE_KEY);
+  if (stored && (args.supported as readonly string[]).includes(stored)) {
+    return stored as SupportedLocale;
+  }
+  const nav = (args.navigatorLanguage ?? '').slice(0, 2).toLowerCase();
+  if ((args.supported as readonly string[]).includes(nav)) {
+    return nav as SupportedLocale;
+  }
+  return args.supported[0] as SupportedLocale;
+}
+
+function createActiveLocale(): Writable<SupportedLocale> & { bootstrap: () => void } {
+  const store = writable<SupportedLocale>('de');
+  let bootstrapped = false;
+
+  function bootstrap() {
+    if (bootstrapped) return;
+    bootstrapped = true;
+    if (typeof window === 'undefined') return;
+    const initial = detectInitialLocale({
+      storage: window.localStorage,
+      navigatorLanguage: window.navigator.language,
+      supported: SUPPORTED_LOCALES
+    });
+    store.set(initial);
+    store.subscribe((v) => {
+      try {
+        window.localStorage.setItem(STORAGE_KEY, v);
+      } catch {
+        // private-mode / quota — ignorieren
+      }
+    });
+  }
+
+  return {
+    subscribe: store.subscribe,
+    set: store.set,
+    update: store.update,
+    bootstrap
+  };
+}
+
+export const activeLocale = createActiveLocale();