fixed so the code compiles

src/auth/google.js

@@ -3,19 +3,29 @@ const { Strategy: GoogleStrategy } = require('passport-google-oauth20');
 const jwt = require('jsonwebtoken');
 const db = require('../db');
 
-async function generateUniqueUsername(base) {
-  const candidate = base.toLowerCase();
-  const taken = await db.user.findFirst({ where: { username: candidate } });
-  if (!taken) return candidate;
+function deriveBase(email) {
+  const local = email.split('@')[0];
+  const sanitized = local
+    .replace(/\./g, '_')
+    .replace(/[^a-zA-Z0-9_]/g, '')
+    .slice(0, 15)
+    .toLowerCase();
+  return sanitized || 'user';
+}
+
+async function generateUniqueUsername(email) {
+  const base = deriveBase(email);
+  const taken = await db.user.findFirst({ where: { username: base } });
+  if (!taken) return base;
   let attempts = 0;
   while (attempts < 20) {
     const suffix = String(Math.floor(1000 + Math.random() * 9000));
-    const username = `${candidate}${suffix}`;
+    const username = `${base}_${suffix}`;
     const collision = await db.user.findFirst({ where: { username } });
     if (!collision) return username;
     attempts++;
   }
-  return `${candidate}${Date.now()}`;
+  return `${base}_${Date.now()}`;
 }
 
 passport.use(
@@ -31,7 +41,7 @@ passport.use(
         let user = await db.user.findUnique({ where: { googleId: profile.id } });
 
         if (!user) {
-          const username = await generateUniqueUsername(email.split('@')[0]);
+          const username = await generateUniqueUsername(email);
           user = await db.user.create({
             data: {
               googleId: profile.id,
@@ -51,7 +61,7 @@ passport.use(
             },
           });
           if (!user.username) {
-            const username = await generateUniqueUsername((user.email ?? '').split('@')[0]);
+            const username = await generateUniqueUsername(user.email ?? '');
             user = await db.user.update({ where: { id: user.id }, data: { username } });
           }
         }