style(admin): the user form asks who, what role, what quota, then what more

The create and edit pages of a user had one form for both, ordered for
editing: permissions first, the name and password folded below them and
the quota folded and closed at the end; a new user's name came last.

Both pages now go Account (name, password, may sign in), Role, Quota,
then Groups and permissions, each section with what it is for beside its
fields. Template editor and Superuser become one Role choice with User:
choosing Superuser hides the quota and permissions, which a superuser
does not need (no quota check applies, every permission is theirs); it
keeps the is_staff it had. The quota is always open: each limit takes a
number from 0, or No limit, which is kept as -1 as before; memory is
entered in GiB and kept in MiB, shown exactly so saving a user again
changes nothing. The button says Create user or Save changes.

admin/forms.py

@@ -1,3 +1,5 @@
+from decimal import ROUND_HALF_UP, Decimal
+
 from django import forms
 from django.conf import settings
 from django.contrib.auth import password_validation
@@ -64,6 +66,14 @@ class GroupForm(forms.ModelForm):
 
 
 class UserForm(UniqueEmailMixin, forms.ModelForm):
+    # one choice for is_staff and is_superuser: a superuser keeps the
+    # is_staff it had (it adds nothing to every permission)
+    role = forms.ChoiceField(
+        widget=forms.RadioSelect,
+        choices=[("user", _("User")), ("template_editor", _("Template editor")), ("superuser", _("Superuser"))],
+        initial="user",
+    )
+
     user_permissions = forms.ModelMultipleChoiceField(
         widget=forms.CheckboxSelectMultiple,
         queryset=Permission.objects.filter(content_type__model="permissionset"),
@@ -87,12 +97,24 @@ class UserForm(UniqueEmailMixin, forms.ModelForm):
             "last_name",
             "email",
             "user_permissions",
-            "is_staff",
             "is_active",
-            "is_superuser",
         ]
-        labels = {"is_staff": _("Template editor")}
-        help_texts = {"is_staff": _("May change and delete the template VMs given to them")}
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        if self.instance.is_superuser:
+            self.initial["role"] = "superuser"
+        elif self.instance.is_staff:
+            self.initial["role"] = "template_editor"
+
+    def clean(self):
+        cleaned = super().clean()
+        role = cleaned.get("role")
+        if role:
+            cleaned["is_superuser"] = self.instance.is_superuser = role == "superuser"
+            if role != "superuser":
+                self.instance.is_staff = role == "template_editor"
+        return cleaned
 
     def permission_rows(self):
         return permission_rows(self["user_permissions"])
@@ -152,16 +174,55 @@ class UserCreateForm(UserForm):
             "last_name",
             "email",
             "user_permissions",
-            "is_staff",
             "is_active",
-            "is_superuser",
         ]
 
 
+# the quota's limits, with the unit each is entered in (memory in GiB, kept in MiB)
+QUOTA_UNITS = {"max_instances": "", "max_cpus": "", "max_memory": "GiB", "max_disk_size": "GiB"}
+
+
 class UserAttributesForm(forms.ModelForm):
+    """The quota: each limit a number from 0 (none allowed) or No limit,
+    which is kept as -1; memory is entered in GiB and kept in MiB."""
+
+    max_instances = forms.IntegerField(label=_("VMs"), min_value=0, required=False)
+    max_cpus = forms.IntegerField(label=_("vCPUs"), min_value=0, required=False)
+    max_memory = forms.DecimalField(label=_("Memory"), min_value=0, required=False)
+    max_disk_size = forms.IntegerField(label=_("Disk"), min_value=0, required=False)
+
     class Meta:
         model = UserAttributes
-        exclude = ["user", "can_clone_instances", "must_change_password"]
+        fields = list(QUOTA_UNITS)
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        for name in QUOTA_UNITS:
+            limit = getattr(self.instance, name)  # a new user's: the model's default
+            self.fields[f"{name}_unlimited"] = forms.BooleanField(label=_("No limit"), required=False, initial=limit == -1)
+            if limit == -1:
+                self.initial[name] = None
+            elif name == "max_memory":
+                # exact: a MiB count over 1024 always ends, so saving it again changes nothing
+                self.initial[name] = format(Decimal(limit) / 1024, "f")
+            else:
+                self.initial[name] = limit
+
+    def clean(self):
+        cleaned = super().clean()
+        for name in QUOTA_UNITS:
+            if cleaned.get(f"{name}_unlimited"):
+                cleaned[name] = -1
+            elif cleaned.get(name) is None:
+                if name not in self.errors:
+                    self.add_error(name, _("Enter a limit or choose No limit."))
+            elif name == "max_memory":
+                cleaned[name] = int((cleaned[name] * 1024).to_integral_value(ROUND_HALF_UP))
+        return cleaned
+
+    def quota_rows(self):
+        """Each limit's field, its No limit box and its unit, for the form page."""
+        return [(self[name], self[f"{name}_unlimited"], unit) for name, unit in QUOTA_UNITS.items()]
 
 
 class AdminPasswordForm(AdminPasswordChangeForm):