From 0fab60b7106a324bf6a6072f76115900e7ea1e17 Mon Sep 17 00:00:00 2001
From: ectasy663 <namansingh4680@gmail.com>
Date: Sun, 20 Sep 2026 12:15:33 +0530
Subject: [PATCH] perf: eliminate demo account switch lag - no more page
 reload, parallel fetches, settings cache

---
 src/app/dashboard/layout.tsx |  28 ++++++-
 src/hooks/useActiveUser.ts   | 142 ++++++++++++++++++++++++-----------
 2 files changed, 124 insertions(+), 46 deletions(-)

diff --git a/src/app/dashboard/layout.tsx b/src/app/dashboard/layout.tsx
index 811021f..7bfedd0 100644
--- a/src/app/dashboard/layout.tsx
+++ b/src/app/dashboard/layout.tsx
@@ -20,7 +20,7 @@ export default function DashboardLayout({ children }: { children: ReactNode }) {
   const [dropdownOpen, setDropdownOpen] = useState(false)
   const dropdownRef = useRef<HTMLDivElement>(null)
   
-  const { userId, user, globalSettings, switchUser, logout, hasAccessTo, loading, trialInfo } = useActiveUser();
+  const { userId, user, globalSettings, switchUser, logout, hasAccessTo, loading, switching, trialInfo } = useActiveUser();
   const [maintenance, setMaintenance] = useState(false);
   const [checkingMaintenance, setCheckingMaintenance] = useState(true);
 
@@ -75,6 +75,22 @@ export default function DashboardLayout({ children }: { children: ReactNode }) {
 
   return (
     <div className="flex h-screen bg-background overflow-hidden text-foreground selection:bg-primary/20">
+      {/* Demo Account Switch — slim top progress bar, no full-page reload */}
+      {switching && (
+        <div className="fixed top-0 left-0 right-0 z-[9999] h-0.5 overflow-hidden">
+          <div
+            className="h-full bg-[#00F0FF] animate-[slideProgress_0.8s_ease-in-out_infinite]"
+            style={{ width: '60%', animation: 'slideProgress 0.9s ease-in-out infinite' }}
+          />
+          <style>{`
+            @keyframes slideProgress {
+              0%   { transform: translateX(-100%); width: 60%; }
+              50%  { transform: translateX(70%);   width: 80%; }
+              100% { transform: translateX(200%);  width: 60%; }
+            }
+          `}</style>
+        </div>
+      )}
       {/* Sidebar */}
       <aside className="w-64 border-r border-border/60 bg-background/95 backdrop-blur-xl flex flex-col hidden md:flex relative">
         {/* Subtle gradient overlay */}
@@ -350,11 +366,17 @@ export default function DashboardLayout({ children }: { children: ReactNode }) {
             {/* Demo Switcher — only visible when logged in as a known demo account */}
             {isDemoUser(userId) && (
               <div className="flex items-center gap-2">
-                <span className="text-xs text-muted-foreground font-bold hidden lg:inline">Demo:</span>
+                {switching && (
+                  <span className="text-xs text-[#00F0FF] font-bold animate-pulse hidden lg:inline">Switching…</span>
+                )}
+                {!switching && (
+                  <span className="text-xs text-muted-foreground font-bold hidden lg:inline">Demo:</span>
+                )}
                 <select 
                   value={userId}
+                  disabled={switching}
                   onChange={(e) => switchUser(e.target.value)}
-                  className="bg-secondary border border-border text-foreground px-2.5 py-1.5 rounded-xl text-xs font-bold focus:ring-2 focus:ring-[#00F0FF] outline-none cursor-pointer hover:bg-secondary/80 transition-colors"
+                  className="bg-secondary border border-border text-foreground px-2.5 py-1.5 rounded-xl text-xs font-bold focus:ring-2 focus:ring-[#00F0FF] outline-none cursor-pointer hover:bg-secondary/80 transition-colors disabled:opacity-50 disabled:cursor-wait"
                 >
                   <option value={DEMO_USERS.NEHA.id}>Neha Verma (AI Coach)</option>
                   <option value={DEMO_USERS.AI_COACH.id}>Rahul (AI Coach)</option>
diff --git a/src/hooks/useActiveUser.ts b/src/hooks/useActiveUser.ts
index b28670f..f7ee122 100644
--- a/src/hooks/useActiveUser.ts
+++ b/src/hooks/useActiveUser.ts
@@ -1,6 +1,6 @@
 "use client";
 
-import { useEffect, useState, useCallback } from "react";
+import { useEffect, useState, useCallback, useRef } from "react";
 
 export interface UserProfile {
   id: string;
@@ -99,6 +99,29 @@ export function computeTrialInfo(user: UserProfile | null, globalSettings: any):
   };
 }
 
+// ── Global in-memory settings cache ─────────────────────────────────────────
+// Settings rarely change; cache them for 60s so every user switch doesn't
+// re-hit the backend. On a full page load the cache is cold — fine.
+let cachedSettings: any = null;
+let settingsCacheExpiry = 0;
+
+async function fetchSettings(): Promise<any> {
+  const now = Date.now();
+  if (cachedSettings && now < settingsCacheExpiry) return cachedSettings;
+
+  try {
+    const res = await fetch(`/api/admin/settings`, { cache: "no-store" });
+    if (res.ok) {
+      cachedSettings = await res.json();
+      settingsCacheExpiry = now + 60_000; // cache for 60 seconds
+      return cachedSettings;
+    }
+  } catch {
+    // silently return stale cache if available
+  }
+  return cachedSettings ?? null;
+}
+
 export function useActiveUser() {
   const [userId, setUserIdState] = useState<string>(() => {
     if (typeof window !== "undefined") {
@@ -110,16 +133,24 @@ export function useActiveUser() {
   const [user, setUser] = useState<UserProfile | null>(null);
   const [globalSettings, setGlobalSettings] = useState<any>(null);
   const [loading, setLoading] = useState(true);
+  const [switching, setSwitching] = useState(false);
   const [error, setError] = useState<string | null>(null);
-  const failCountRef = { current: 0 };
+  // Use a ref for fail count so it doesn't cause re-renders
+  const failCountRef = useRef(0);
+  // Track the active userId in a ref to avoid stale closures in poll interval
+  const activeUserIdRef = useRef(userId);
 
   const fetchUserProfile = useCallback(async (id: string, isPoll: boolean = false) => {
     if (!isPoll) setLoading(true);
     setError(null);
+
     try {
-      const res = await fetch(`/api/users/${id}`);
-      const settingsRes = await fetch(`/api/admin/settings`, { cache: "no-store" });
-      
+      // ── PERF FIX: run both fetches in PARALLEL instead of sequentially ──
+      const [res, settingsData] = await Promise.all([
+        fetch(`/api/users/${id}`),
+        fetchSettings(),
+      ]);
+
       if (!res.ok) {
         if (!isPoll) {
           setError("Failed to fetch user profile");
@@ -127,13 +158,13 @@ export function useActiveUser() {
         }
         return;
       }
-      
+
       const data = await res.json();
-      if (settingsRes.ok) {
-        const settingsData = await settingsRes.json();
+
+      if (settingsData) {
         setGlobalSettings(settingsData);
       }
-      
+
       failCountRef.current = 0;
 
       // Single Active Session Check
@@ -150,8 +181,7 @@ export function useActiveUser() {
 
       setUser(data);
     } catch (err: any) {
-      // Network error (backend down / restarting) — only surface on initial load
-      failCountRef.current = (failCountRef.current || 0) + 1;
+      failCountRef.current += 1;
       if (!isPoll) {
         console.warn("Backend unreachable, will retry:", err.message);
         setError("Backend unreachable — retrying...");
@@ -162,55 +192,80 @@ export function useActiveUser() {
     }
   }, []);
 
-  // Initial fetch
+  // Initial fetch on mount
   useEffect(() => {
     if (typeof window !== "undefined") {
       const storedId = localStorage.getItem("activeUserId") || DEFAULT_USER_ID;
+      activeUserIdRef.current = storedId;
       setUserIdState(storedId);
       fetchUserProfile(storedId);
     }
   }, [fetchUserProfile]);
 
-  // Session validity polling — only runs when we already have a user
+  // Session validity polling — runs against the ref so switching userId
+  // doesn't restart the interval and cause an immediate double-fetch
   useEffect(() => {
     if (typeof window === "undefined") return;
 
-    const handleUpdate = () => fetchUserProfile(userId);
+    const handleUpdate = () => fetchUserProfile(activeUserIdRef.current);
     window.addEventListener("pragativeer-user-updated", handleUpdate);
 
-    // Poll every 30s (was 10s — less aggressive, kinder on backend restarts)
+    // Poll every 30s (less aggressive, kinder on backend)
     const interval = setInterval(() => {
-      fetchUserProfile(userId, true);
-    }, 30000);
+      fetchUserProfile(activeUserIdRef.current, true);
+    }, 30_000);
 
     return () => {
       window.removeEventListener("pragativeer-user-updated", handleUpdate);
       clearInterval(interval);
     };
-  }, [userId, fetchUserProfile]);
-
+  // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, []); // Only run once — ref keeps the latest userId
 
   const switchUser = useCallback(async (newId: string) => {
-    if (typeof window !== "undefined") {
-      document.cookie = `auth_token=${newId}; path=/; max-age=2592000; SameSite=Lax`;
-      const sessionToken = crypto.randomUUID();
-      localStorage.setItem("active_session_token", sessionToken);
-      
-      try {
-        await fetch(`/api/users/${newId}/session`, {
-          method: 'POST',
-          headers: { 'Content-Type': 'application/json' },
-          body: JSON.stringify({ session_token: sessionToken })
-        });
-      } catch (err) {
-        console.error("Failed to set session", err);
+    if (typeof window === "undefined" || newId === activeUserIdRef.current) return;
+
+    setSwitching(true);
+
+    // ── Update cookie + localStorage immediately (optimistic) ───────────────
+    document.cookie = `auth_token=${newId}; path=/; max-age=2592000; SameSite=Lax`;
+    const sessionToken = crypto.randomUUID();
+    localStorage.setItem("active_session_token", sessionToken);
+    localStorage.setItem("activeUserId", newId);
+
+    // Update refs and state before awaiting network
+    activeUserIdRef.current = newId;
+    setUserIdState(newId);
+    setUser(null); // Clear old user immediately so stale data isn't shown
+
+    try {
+      // ── Run session update + new user profile fetch IN PARALLEL ─────────
+      const [_, newUserRes] = await Promise.all([
+        // Fire-and-forget session token update
+        fetch(`/api/users/${newId}/session`, {
+          method: "POST",
+          headers: { "Content-Type": "application/json" },
+          body: JSON.stringify({ session_token: sessionToken }),
+        }).catch(() => {}), // ignore failure — non-critical
+        // Fetch the new user's profile immediately
+        fetch(`/api/users/${newId}`),
+      ]);
+
+      if (newUserRes && newUserRes.ok) {
+        const data = await newUserRes.json();
+        setUser(data);
+      } else {
+        // Fallback: use the regular fetch path
+        await fetchUserProfile(newId);
       }
-      
-      localStorage.setItem("activeUserId", newId);
-      setUserIdState(newId);
-      window.location.reload();
+    } catch {
+      // Network error — fall back to full fetch
+      await fetchUserProfile(newId);
+    } finally {
+      setSwitching(false);
     }
-  }, []);
+    // ── NO window.location.reload() — React state update is instant ─────────
+  }, [fetchUserProfile]);
 
   const logout = useCallback(() => {
     if (typeof window !== "undefined") {
@@ -223,11 +278,11 @@ export function useActiveUser() {
 
   const hasAccessTo = useCallback((feature: string): boolean => {
     if (!user) return false;
-    
+
     // Compute effective tier via trial logic
     const { effectiveTier } = computeTrialInfo(user, globalSettings);
     const tier = effectiveTier;
-    
+
     // Core restrictions mapping based on PRD feature matrix
     switch (feature) {
       case "topic-wise-microtests-unlimited":
@@ -241,7 +296,7 @@ export function useActiveUser() {
       case "offline-mode":
       case "pdf-export":
         return tier === "Pro" || tier === "Al_Coach";
-        
+
       case "ai-coach-custom-schedules":
       case "personalized-study-plan":
       case "ai-tutor-doubt-resolution":
@@ -249,7 +304,7 @@ export function useActiveUser() {
       case "ai-readiness-prediction":
       case "ai-tutor-chat":
         return tier === "Al_Coach";
-        
+
       default:
         // Free tier features: DPS (1/day), basic dashboard, basic streak tracking, leaderboard
         return true;
@@ -261,6 +316,7 @@ export function useActiveUser() {
     user,
     globalSettings,
     loading,
+    switching, // expose switching state so layout can show a brief spinner
     error,
     switchUser,
     logout,
@@ -268,7 +324,7 @@ export function useActiveUser() {
     trialInfo: computeTrialInfo(user, globalSettings),
     refreshUser: async () => {
       await fetchUserProfile(userId);
-      window.dispatchEvent(new CustomEvent('pragativeer-user-updated'));
-    }
+      window.dispatchEvent(new CustomEvent("pragativeer-user-updated"));
+    },
   };
 }