Fix runtime default locale resolution

tests/middleware.test.ts

@@ -0,0 +1,118 @@
+import { NextResponse } from "next/server";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+const createMiddlewareMock = vi.fn();
+const intlHandlerMock = vi.fn(() => NextResponse.next());
+
+vi.mock("next-intl/middleware", () => ({
+  default: createMiddlewareMock,
+}));
+
+vi.mock("../lib/admin-routing", () => ({
+  fromDevelopmentAdminPath: (pathname: string) => pathname,
+  getAdminBaseUrl: () => "https://admin.example.com",
+  getRequestHostname: (_forwardedHost: string | null, host: string | null, hostname: string) => host ?? hostname,
+  isDevelopmentAdminPath: () => false,
+  isAdminHost: () => false,
+  hasDedicatedAdminHost: () => false,
+  isInternalAdminPath: () => false,
+  isLegacyAdminPath: () => false,
+  toInternalAdminPath: (pathname: string) => pathname,
+}));
+
+function createMockRequest(url: string) {
+  const nextUrl = new URL(url) as URL & { clone: () => URL };
+  nextUrl.clone = () => new URL(nextUrl.toString());
+
+  return {
+    url,
+    nextUrl,
+    headers: new Headers({
+      host: nextUrl.host,
+    }),
+    cookies: {
+      has: vi.fn(() => false),
+    },
+  };
+}
+
+describe("middleware locale runtime config", () => {
+  beforeEach(() => {
+    vi.resetModules();
+    createMiddlewareMock.mockReset();
+    intlHandlerMock.mockReset();
+    intlHandlerMock.mockReturnValue(NextResponse.next());
+    createMiddlewareMock.mockReturnValue(intlHandlerMock);
+  });
+
+  afterEach(() => {
+    vi.unstubAllGlobals();
+  });
+
+  it("passes the runtime default locale into next-intl middleware", async () => {
+    vi.stubGlobal(
+      "fetch",
+      vi.fn(async () => ({
+        ok: true,
+        json: async () => ({
+          defaultLocale: "ar",
+          maintenanceEnabled: false,
+        }),
+      })),
+    );
+
+    const { default: middleware } = await import("../middleware");
+    const request = createMockRequest("https://example.com/");
+
+    await middleware(request as never);
+
+    expect(createMiddlewareMock).toHaveBeenCalledTimes(1);
+    expect(createMiddlewareMock).toHaveBeenCalledWith(
+      expect.objectContaining({
+        defaultLocale: "ar",
+      }),
+    );
+    expect(intlHandlerMock).toHaveBeenCalledTimes(1);
+  });
+
+  it("falls back safely when the runtime locale lookup fails", async () => {
+    vi.stubGlobal(
+      "fetch",
+      vi.fn(async () => {
+        throw new Error("network failed");
+      }),
+    );
+
+    const { default: middleware } = await import("../middleware");
+    const request = createMockRequest("https://example.com/");
+
+    await middleware(request as never);
+
+    expect(createMiddlewareMock).toHaveBeenCalledWith(
+      expect.objectContaining({
+        defaultLocale: "de",
+      }),
+    );
+  });
+
+  it("redirects maintenance traffic using the runtime default locale", async () => {
+    vi.stubGlobal(
+      "fetch",
+      vi.fn(async () => ({
+        ok: true,
+        json: async () => ({
+          defaultLocale: "ar",
+          maintenanceEnabled: true,
+        }),
+      })),
+    );
+
+    const { default: middleware } = await import("../middleware");
+    const request = createMockRequest("https://example.com/");
+
+    const response = await middleware(request as never);
+
+    expect(response.headers.get("location")).toBe("https://example.com/coming-soon");
+    expect(intlHandlerMock).not.toHaveBeenCalled();
+  });
+});