Cannot set username that is similar to an alias we don't own

apps/member/views.py

@@ -4,6 +4,7 @@
 # SPDX-License-Identifier: GPL-3.0-or-later
 from dal import autocomplete
 from django.contrib.auth.mixins import LoginRequiredMixin
+from django.core.exceptions import ValidationError
 from django.utils.translation import gettext_lazy as _
 from django.views.generic import CreateView, ListView, DetailView, UpdateView
 from django.http import HttpResponseRedirect
@@ -14,7 +15,7 @@ from django.db.models import Q
 
 from django_tables2.views import SingleTableView
 
-
+from note.models import Alias, Note, NoteUser
 from .models import Profile, Club, Membership
 from .forms import  SignUpForm, ProfileForm, ClubForm,MembershipForm, MemberFormSet,FormSetHelper
 from .tables import ClubTable,UserTable
@@ -57,13 +58,38 @@ class UserUpdateView(LoginRequiredMixin,UpdateView):
     second_form = ProfileForm
     def get_context_data(self,**kwargs):
         context = super().get_context_data(**kwargs)
-        context["profile_form"] = self.second_form(instance=context['user'].profile)
+        context['user_modified'] = context['user']
+        context['user'] = self.request.user
+        context["profile_form"] = self.second_form(instance=context['user_modified'].profile)
 
         return context
 
+    def get_form(self, form_class=None):
+        from django.forms import forms
+        form: forms.Form = super().get_form(form_class)
+        if 'username' not in form.data:
+            return form
+
+        new_username = form.data['username']
+
+        note = NoteUser.objects.filter(alias__normalized_name=Alias.normalize(new_username))
+        if note.exists() and note.get().user != self.request.user:
+            form.add_error('username', _("An alias with a similar name already exists."))
+
+        return form
+
+
     def form_valid(self, form):
         profile_form = ProfileForm(data=self.request.POST,instance=self.request.user.profile)
         if form.is_valid() and profile_form.is_valid():
+            new_username = form.data['username']
+            alias = Alias.objects.filter(name=new_username)
+            if not alias.exists():
+                similar = Alias.objects.filter(normalized_name=Alias.normalize(new_username))
+                if similar.exists():
+                    similar.delete()
+                note = NoteUser.objects.filter(alias__normalized_name=Alias.normalize(self.request.user.username)).get()
+                Alias(name=new_username, note=note).save()
             user = form.save()
             profile  = profile_form.save(commit=False)
             profile.user = user