fix(nav): fix exam flow navigation

chore(zustand): refactor auth code for zustand store

app/exam/exam-screen/page.tsx

@@ -10,7 +10,6 @@ import { useTimerStore } from "@/stores/timerStore";
 
 export default function ExamPage() {
   const router = useRouter();
-  const pathname = usePathname();
   const searchParams = useSearchParams();
   const test_id = searchParams.get("test_id") || "";
   const type = searchParams.get("type") || "";
@@ -23,55 +22,46 @@ export default function ExamPage() {
 
   // Start exam + timer automatically
   useEffect(() => {
-    if (type && test_id) {
-      startExam(type, test_id).then((fetchedTest) => {
-        if (fetchedTest?.metadata.time_limit_minutes) {
-          setStatus("in-progress"); // ✅ make sure exam status is set here
-          resetTimer(fetchedTest.metadata.time_limit_minutes * 60, () => {
-            // Timer ended → auto-submit
-            setStatus("finished");
-            stopTimer();
-            submitExam(type);
-            router.replace(`/exam/results`);
-          });
-        }
-      });
-    }
+    if (!type || !test_id) return;
+
+    const initExam = async () => {
+      const fetchedTest = await startExam(type, test_id);
+
+      if (!fetchedTest) return;
+
+      setStatus("in-progress");
+
+      const timeLimit = fetchedTest.metadata.time_limit_minutes;
+      if (timeLimit) {
+        resetTimer(timeLimit * 60, async () => {
+          // Auto-submit when timer ends
+          stopTimer();
+          setStatus("finished");
+          await submitExam(type);
+          router.replace("/exam/results");
+        });
+      }
+    };
+
+    initExam();
   }, [
     type,
     test_id,
     startExam,
     resetTimer,
+    stopTimer,
     submitExam,
     router,
     setStatus,
-    stopTimer,
   ]);
 
-  // useEffect(() => {
-  //   const handlePopState = (event: PopStateEvent) => {
-  //     if (status === "in-progress") {
-  //       const confirmExit = window.confirm(
-  //         "Are you sure you want to quit the exam?"
-  //       );
-
-  //       if (confirmExit) {
-  //         setStatus("finished");
-  //         stopTimer();
-  //         cancelExam();
-  //         router.replace(`/categories/${type}s`);
-  //       } else {
-  //         // User canceled → push them back to current page
-  //         router.replace(pathname, { scroll: false });
-  //       }
-  //     } else {
-  //       router.replace(`/categories/${type}s`);
-  //     }
-  //   };
-
-  //   window.addEventListener("popstate", handlePopState);
-  //   return () => window.removeEventListener("popstate", handlePopState);
-  // }, [status, router, pathname, type, setStatus, stopTimer, cancelExam]);
+  if (isSubmitting) {
+    return (
+      <div className="min-h-screen bg-gray-50 flex items-center justify-center">
+        <p className="text-lg font-medium text-gray-900">Submitting exam...</p>
+      </div>
+    );
+  }
 
   if (!test) {
     return (
@@ -85,12 +75,18 @@ export default function ExamPage() {
   }
 
   const handleSubmitExam = async (type: string) => {
+    setIsSubmitting(true);
+    stopTimer();
+
     try {
-      setStatus("finished"); // ✅ mark exam finished
-      stopTimer();
-      setIsSubmitting(true);
-      await submitExam(type);
-      router.replace(`/exam/results`); // ✅ replace to prevent back nav
+      const result = await submitExam(type); // throws if fails
+
+      if (!result) throw new Error("Submission failed");
+
+      router.replace("/exam/results"); // navigate
+    } catch (err) {
+      console.error("Submit exam failed:", err);
+      alert("Failed to submit exam. Please try again.");
     } finally {
       setIsSubmitting(false);
     }
@@ -137,6 +133,3 @@ export default function ExamPage() {
     </div>
   );
 }
-function cancelExam() {
-  throw new Error("Function not implemented.");
-}