Feature: Updating Products Service and Locale MIddleware

src/Localization/LocaleMiddleware.php

@@ -7,6 +7,8 @@ use Illuminate\Http\Request;
 use Illuminate\Support\Collection;
 use Illuminate\Support\Facades\App;
 use Illuminate\Support\Facades\Cache;
+use Illuminate\Support\Facades\URL;
+use Illuminate\Support\Facades\View;
 use Lunar\Models\Language;
 use Symfony\Component\HttpFoundation\Response;
 
@@ -33,6 +35,13 @@ class LocaleMiddleware
         $request->attributes->set('locale', $language->code);
         $request->attributes->set('language', $language);
 
+        // Lets route() calls omit {locale} anywhere in the request lifecycle
+        // (controllers, views) — without this, every route() call would need
+        // locale passed explicitly every time.
+        URL::defaults(['locale' => $language->code]);
+
+        $this->shareLocaleViewData($request, $language, $languages);
+
         return $next($request);
     }
 
@@ -41,6 +50,38 @@ class LocaleMiddleware
         Cache::forget(self::CACHE_KEY);
     }
 
+    /**
+     * The store's default language code (e.g. 'el') - the fixed fallback other
+     * locale-aware code (Modules\Core\Catalog\ProductService) should use, as
+     * opposed to config('app.locale') which App::setLocale() mutates per
+     * request and so can't serve as a stable fallback.
+     */
+    public static function defaultLocale(): ?string
+    {
+        return (new self)->availableLanguages()->firstWhere('default', true)?->code;
+    }
+
+    /**
+     * Shares the current/alternate locale (and the alternate's URL) with all
+     * views, so the header language switcher and layout hreflang tags don't
+     * have to recompute it.
+     */
+    private function shareLocaleViewData(Request $request, Language $language, Collection $languages): void
+    {
+        $altLanguage = $languages->firstWhere('code', '!=', $language->code);
+        $route = $request->route();
+        $routeName = $route?->getName();
+
+        View::share('currentLocale', $language->code);
+        View::share('altLocale', $altLanguage?->code);
+        View::share(
+            'altLocaleUrl',
+            $altLanguage && $routeName
+                ? route($routeName, array_merge($route->parameters(), ['locale' => $altLanguage->code]))
+                : ($altLanguage ? url('/'.$altLanguage->code) : null),
+        );
+    }
+
     private function redirectToLocalizedUrl(Request $request, Collection $languages): Response
     {
         $locale = $this->negotiateLocale($request, $languages);