Handle auth callback params on landing and redirect signed-in users

Author: felmonon

src/app/page.tsx

@@ -1,6 +1,6 @@
 'use client';
 
-import { useRef, useState } from 'react';
+import { useEffect, useRef, useState } from 'react';
 import { useInView, motion, AnimatePresence } from 'framer-motion';
 import {
   Check,
@@ -21,6 +21,7 @@ import {
   TrendingUp,
 } from 'lucide-react';
 import Link from 'next/link';
+import { createClient } from '@/lib/supabase/client';
 
 /* ─────────────────────────────────────────────────────────
    ANIMATION PRIMITIVES
@@ -600,6 +601,28 @@ const proPlanFeatures = [
    ═════════════════════════════════════════════════════════ */
 
 export default function LandingPage() {
+  useEffect(() => {
+    const url = new URL(window.location.href);
+    const code = url.searchParams.get('code');
+    const tokenHash = url.searchParams.get('token_hash');
+
+    // If auth params accidentally land on "/", forward to callback to complete session exchange.
+    if (code || tokenHash) {
+      window.location.replace(`/auth/callback${url.search}`);
+      return;
+    }
+
+    // Keep logged-in users inside the app instead of showing marketing landing.
+    const supabase = createClient();
+    void supabase.auth.getUser().then(({ data: { user } }) => {
+      if (user) {
+        window.location.replace('/app/today');
+      }
+    }).catch(() => {
+      // Ignore errors here; unauthenticated users should still see the landing page.
+    });
+  }, []);
+
   return (
     <div className="min-h-screen bg-bg-primary font-sans relative">
       {/* Noise texture */}