added a better way to show if username or email is taken

app.py

@@ -3,6 +3,7 @@ from functools import wraps
 from flask import Flask, render_template, redirect, request, url_for, session, flash
 from flask_sqlalchemy import SQLAlchemy
 from werkzeug.security import generate_password_hash, check_password_hash
+from sqlalchemy.exc import IntegrityError
 
 app = Flask(__name__)
 
@@ -25,29 +26,41 @@ def login_required(view_func):
     @wraps(view_func)
     def wrapped(*args, **kwargs):
         if 'user_id' not in session:
-            flash('Please sign in to view that page.')
+            flash('sign in to view that page.')
             return redirect(url_for('signin'))
         return view_func(*args, **kwargs)
     return wrapped
 
 
+from sqlalchemy.exc import IntegrityError
+
 @app.route('/submit-form', methods=['POST'])
 def handle_submission():
-    form_username = request.form.get('username')
-    form_email = request.form.get('email')
-    form_password = request.form.get('password')
-    
+    form_username = (request.form.get('username') or '').strip()
+    form_email = (request.form.get('email') or '').strip().lower()
+    form_password = request.form.get('password') or ''
+
+    if not form_username or not form_email or not form_password:
+        return render_template('signup.html', error="All fields are required"), 400
+
+    if len(form_password) < 8:
+        return render_template('signup.html', error="Password must be at least 8 characters"), 400
+
     if User.query.filter_by(username=form_username).first():
-        return "<h3>Username taken!</h3>", 400
+        return render_template('signup.html', user_taken="Username has already been taken"), 400
     if User.query.filter_by(email=form_email).first():
-        return "<h3>Email already registered!</h3>", 400
-    
+        return render_template('signup.html', email_taken="Email has already been used"), 400
+
     hashed_password = generate_password_hash(form_password)
-    
     new_user = User(username=form_username, email=form_email, password_hash=hashed_password)
-    db.session.add(new_user)
-    db.session.commit()
-    
+
+    try:
+        db.session.add(new_user)
+        db.session.commit()
+    except IntegrityError:
+        db.session.rollback()
+        return render_template('signup.html', error="Username or email already taken"), 400
+
     return render_template('signup.html', success_message="Account successfully created")