bug fixes

app.py

@@ -201,22 +201,26 @@ def login():
         if user and check_password_hash(user.password, request.form.get("password")):
             login_user(user)
             return redirect(url_for("dashboard"))
-        flash("Invalid credentials")
+        flash("Invalid credentials",'error')
     return render_template("login.html")
 
 
 @app.route("/register", methods=["GET", "POST"])
 def register():
-    if request.method == "POST":
-        new_user = User(
-            username=request.form.get("username"),
-            password=generate_password_hash(
-                request.form.get("password"), method="pbkdf2:sha256"
-            ),
-        )
+    if request.method == 'POST':
+        username = request.form.get('username')
+        password = request.form.get('password')
+
+        existing_user = User.query.filter_by(username=username).first()
+        
+        if existing_user:
+            flash('That username is already taken. Please choose a different one.', 'error')
+            return redirect(url_for('register'))
+
+        new_user = User(username=username, password=generate_password_hash(password))
         db.session.add(new_user)
         db.session.commit()
-        return redirect(url_for("/"))
+        return redirect(url_for("dashboard"))
     return render_template("register.html")