Add alternate accounts to the user model

Introduce a way to store alternate accounts on the user, and add the
`PATCH /bot/users/<id:str>/alts` endpoint, which allows updating the
user's alt accounts to the alt accounts in the request..

pydis_site/apps/api/migrations/0093_user_alts.py

@@ -0,0 +1,37 @@
+# Generated by Django 5.0 on 2023-12-12 09:01
+
+import django.db.models.deletion
+import pydis_site.apps.api.models.mixins
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('api', '0092_remove_redirect_filter_list'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='UserAltRelationship',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('source', models.ForeignKey(help_text='The source of this user to alternate account relationship', on_delete=django.db.models.deletion.CASCADE, to='api.user', verbose_name='Source')),
+                ('target', models.ForeignKey(help_text='The target of this user to alternate account relationship', on_delete=django.db.models.deletion.CASCADE, related_name='+', to='api.user', verbose_name='Target')),
+            ],
+            bases=(pydis_site.apps.api.models.mixins.ModelReprMixin, models.Model),
+        ),
+        migrations.AddField(
+            model_name='user',
+            name='alts',
+            field=models.ManyToManyField(help_text='Known alternate accounts of this user. Manually linked.', through='api.UserAltRelationship', to='api.user', verbose_name='Alternative accounts'),
+        ),
+        migrations.AddConstraint(
+            model_name='useraltrelationship',
+            constraint=models.UniqueConstraint(fields=('source', 'target'), name='api_useraltrelationship_unique_relationships'),
+        ),
+        migrations.AddConstraint(
+            model_name='useraltrelationship',
+            constraint=models.CheckConstraint(check=models.Q(('source', models.F('target')), _negated=True), name='api_useraltrelationship_prevent_alt_to_self'),
+        ),
+    ]

pydis_site/apps/api/models/bot/user.py

@@ -61,6 +61,12 @@ class User(ModelReprMixin, models.Model):
         help_text="Whether this user is in our server.",
         verbose_name="In Guild"
     )
+    alts = models.ManyToManyField(
+        'self',
+        through='UserAltRelationship',
+        help_text="Known alternate accounts of this user. Manually linked.",
+        verbose_name="Alternative accounts"
+    )
 
     def __str__(self):
         """Returns the name and discriminator for the current user, for display purposes."""
@@ -86,3 +92,34 @@ def username(self) -> str:
         For usability in read-only fields such as Django Admin.
         """
         return str(self)
+
+class UserAltRelationship(ModelReprMixin, models.Model):
+    """A relationship between a Discord user and its alts."""
+
+    source = models.ForeignKey(
+        User,
+        on_delete=models.CASCADE,
+        verbose_name="Source",
+        help_text="The source of this user to alternate account relationship",
+    )
+    target = models.ForeignKey(
+        User,
+        on_delete=models.CASCADE,
+        verbose_name="Target",
+        related_name='+',
+        help_text="The target of this user to alternate account relationship",
+    )
+
+    class Meta:
+        """Add constraints to prevent users from being an alt of themselves."""
+
+        constraints = [
+            models.UniqueConstraint(
+                name="%(app_label)s_%(class)s_unique_relationships",
+                fields=["source", "target"]
+            ),
+            models.CheckConstraint(
+                name="%(app_label)s_%(class)s_prevent_alt_to_self",
+                check=~models.Q(source=models.F("target")),
+            ),
+        ]

pydis_site/apps/api/serializers.py

@@ -669,7 +669,7 @@ def update(self, queryset: QuerySet, validated_data: list) -> list:
         return updated
 
 
-class UserSerializer(ModelSerializer):
+class UserSerializer(FrozenFieldsMixin, ModelSerializer):
     """A class providing (de-)serialization of `User` instances."""
 
     # ID field must be explicitly set as the default id field is read-only.
@@ -679,7 +679,9 @@ class Meta:
         """Metadata defined for the Django REST Framework."""
 
         model = User
-        fields = ('id', 'name', 'discriminator', 'roles', 'in_guild')
+        fields = ('id', 'name', 'discriminator', 'roles', 'in_guild', 'alts')
+        # This should be edited on a separate endpoint only
+        frozen_fields = ('alts',)
         depth = 1
         list_serializer_class = UserListSerializer
 

pydis_site/apps/api/tests/test_infractions.py

@@ -747,7 +747,7 @@ def setUpTestData(cls):
     def check_expanded_fields(self, infraction):
         for key in ('user', 'actor'):
             obj = infraction[key]
-            for field in ('id', 'name', 'discriminator', 'roles', 'in_guild'):
+            for field in ('id', 'name', 'discriminator', 'roles', 'in_guild', 'alts'):
                 self.assertTrue(field in obj, msg=f'field "{field}" missing from {key}')
 
     def test_list_expanded(self):

pydis_site/apps/api/tests/test_users.py

@@ -60,6 +60,7 @@ def setUpTestData(cls):
     def test_accepts_valid_data(self):
         url = reverse('api:bot:user-list')
         data = {
+            'alts': [],
             'id': 42,
             'name': "Test",
             'discriminator': 42,
@@ -199,13 +200,15 @@ def test_multiple_users_patch(self):
         url = reverse("api:bot:user-bulk-patch")
         data = [
             {
+                "alts": [],
                 "id": 1,
                 "name": "User 1 patched!",
                 "discriminator": 1010,
                 "roles": [self.role_developer.id],
                 "in_guild": False
             },
             {
+                "alts": [],
                 "id": 2,
                 "name": "User 2 patched!"
             }
@@ -646,3 +649,120 @@ def test_search_lookup_of_unknown_user(self) -> None:
         result = response.json()
         self.assertEqual(result['count'], 0)
         self.assertEqual(result['results'], [])
+
+
+class UserAltUpdateTests(AuthenticatedAPITestCase):
+    @classmethod
+    def setUpTestData(cls):
+        cls.user_1 = User.objects.create(
+            id=12095219,
+            name=f"Test user {random.randint(100, 1000)}",
+            discriminator=random.randint(1, 9999),
+            in_guild=True,
+        )
+        cls.user_2 = User.objects.create(
+            id=18259125,
+            name=f"Test user {random.randint(100, 1000)}",
+            discriminator=random.randint(1, 9999),
+            in_guild=True,
+        )
+
+    def test_adding_existing_alts(self) -> None:
+        url = reverse('api:bot:user-alts', args=(self.user_1.id,))
+        data = [self.user_2.id]
+        response = self.client.patch(url, data)
+        self.assertEqual(response.status_code, 200)
+
+        updated_user = response.json()
+        self.assertEqual(len(updated_user['alts']), 1)
+        self.assertEqual(updated_user['alts'][0]['id'], self.user_2.id)
+
+        self.user_1.refresh_from_db()
+        self.user_2.refresh_from_db()
+
+        self.assertQuerySetEqual(self.user_1.alts.all(), [self.user_2])
+        self.assertQuerySetEqual(self.user_2.alts.all(), [self.user_1])
+
+    def test_removing_existing_alts(self) -> None:
+        self.user_1.alts.set((self.user_2.id,))
+        self.user_1.save()
+
+        data = []
+        url = reverse('api:bot:user-alts', args=(self.user_1.id,))
+        response = self.client.patch(url, data)
+
+        self.assertEqual(response.status_code, 200)
+        updated_user = response.json()
+        self.assertEqual(updated_user['alts'], [])
+
+        self.user_1.refresh_from_db()
+        self.user_2.refresh_from_db()
+
+        self.assertFalse(self.user_1.alts.all().exists())
+        self.assertFalse(self.user_2.alts.all().exists())
+
+    def test_adding_alt_to_user_that_does_not_exist(self) -> None:
+        """Patching a user's alts for a user that doesn't exist should return a 404."""
+        url = reverse('api:bot:user-alts', args=(self.user_1.id + self.user_2.id,))
+        data = [self.user_2.id]
+        response = self.client.patch(url, data)
+        self.assertEqual(response.status_code, 404)
+
+    def test_adding_alt_that_does_not_exist_to_user(self) -> None:
+        """Patching a user's alts with an alt that is unknown should return a 400."""
+        url = reverse('api:bot:user-alts', args=(self.user_1.id,))
+        data = [self.user_1.id + self.user_2.id]
+        response = self.client.patch(url, data)
+        self.assertEqual(response.status_code, 400)
+        self.assertEqual(response.json(), {
+            'non_field_errors': ["One or more unknown user IDs were passed"]
+        })
+
+    def test_cannot_add_self_as_alt_account(self) -> None:
+        """The existing account may not be an alt of itself."""
+        url = reverse('api:bot:user-alts', args=(self.user_1.id,))
+        data = [self.user_1.id]
+        response = self.client.patch(url, data)
+        self.assertEqual(response.status_code, 400)
+        self.assertEqual(response.json(), {
+            'non_field_errors': ["The user may not be an alternate account of itself"]
+        })
+
+    def test_cannot_update_alts_on_regular_user_patch_route(self) -> None:
+        """The regular user update route does not allow editing the alts."""
+        url = reverse('api:bot:user-detail', args=(self.user_1.id,))
+        data = {'alts': [self.user_2.id]}
+        response = self.client.patch(url, data)
+        self.assertEqual(response.status_code, 200)  # XXX: This seems to be a DRF bug
+        self.assertEqual(response.json()['alts'], [])
+
+        self.user_1.refresh_from_db()
+        self.assertQuerySetEqual(self.user_1.alts.all(), ())
+        self.user_2.refresh_from_db()
+        self.assertQuerySetEqual(self.user_2.alts.all(), ())
+
+    def test_cannot_update_alts_on_bulk_user_patch_route(self) -> None:
+        """The bulk user update route does not allow editing the alts."""
+        url = reverse('api:bot:user-bulk-patch')
+        data = [{'id': self.user_1.id, 'alts': [self.user_2.id]}]
+        response = self.client.patch(url, data)
+        self.assertEqual(response.status_code, 400)
+        self.assertEqual(response.json(), {'non_field_errors': ['Insufficient data provided.']})
+
+        self.user_1.refresh_from_db()
+        self.assertQuerySetEqual(self.user_1.alts.all(), ())
+        self.user_2.refresh_from_db()
+        self.assertQuerySetEqual(self.user_2.alts.all(), ())
+
+    def test_user_bulk_patch_does_not_discard_alts(self) -> None:
+        """The bulk user update route should not modify the alts."""
+        url = reverse('api:bot:user-bulk-patch')
+        self.user_1.alts.set((self.user_2,))
+        data = [{'id': self.user_1.id, 'name': "Joe Armstrong"}]
+        response = self.client.patch(url, data)
+        self.assertEqual(response.status_code, 200)
+
+        self.user_1.refresh_from_db()
+        self.assertQuerySetEqual(self.user_1.alts.all(), (self.user_2,))
+        self.user_2.refresh_from_db()
+        self.assertQuerySetEqual(self.user_2.alts.all(), (self.user_1,))

pydis_site/apps/api/viewsets/bot/user.py

@@ -1,5 +1,6 @@
 from collections import OrderedDict
 
+from django.db import IntegrityError
 from django.db.models import Q
 from django_filters.rest_framework import DjangoFilterBackend
 from rest_framework import fields, status
@@ -203,8 +204,9 @@ class UserViewSet(ModelViewSet):
     - 404: if the user with the given `snowflake` could not be found
 
     ### PATCH /bot/users/<snowflake:int>
-    Update the user with the given `snowflake`.
-    All fields in the request body are optional.
+    Update the user with the given `snowflake`. All fields in the request body
+    are optional.  Note that editing the `'alts'` field is not possible this
+    way, use the `alts` endpoint documented below for this.
 
     #### Request body
     >>> {
@@ -220,9 +222,24 @@ class UserViewSet(ModelViewSet):
     - 400: if the request body was invalid, see response body for details
     - 404: if the user with the given `snowflake` could not be found
 
+    ### PATCH /bot/users/<snowflake:int>/alts
+    Update the alternative accounts for the given user snowflake. The request
+    body contains the user IDs to link to this user, as a plain list. IDs will
+    be linked symmetrically. Returns the updated user.
+
+    #### Request body
+    >>> [int, ...]
+
+    #### Status codes
+    - 200: returned on success
+    - 400: if the request body was invalid, including if one of the users in
+      the request body could not be found in the database
+    - 404: if the user with the given `snowflake` could not be found
+
     ### BULK PATCH /bot/users/bulk_patch
-    Update users with the given `ids` and `details`.
-    `id` field and at least one other field is mandatory.
+    Update users with the given `ids` and `details`. `id` field and at least
+    one other field is mandatory. Note that editing the `'alts'` field is not
+    possible using this endpoint.
 
     #### Request body
     >>> [
@@ -284,6 +301,30 @@ def bulk_patch(self, request: Request) -> Response:
 
         return Response(serializer.data, status=status.HTTP_200_OK)
 
+    @action(detail=True, methods=['PATCH'], name='user-alts-update', url_name='alts', url_path='alts')
+    def update_alts(self, request: Request, pk: str) -> Response:
+        """Update the user's alternate accounts to the given list."""
+        user = self.get_object()
+        if not isinstance(request.data, list):
+            raise ParseError(detail={"non_field_errors": ["Request body should be a list"]})
+        if not all(isinstance(item, int) for item in request.data):
+            raise ParseError(detail={"non_field_errors": ["List payload should only contain numbers"]})
+        users = User.objects.filter(id__in=request.data)
+        if len(users) != len(request.data):
+            raise ParseError(detail={"non_field_errors": ["One or more unknown user IDs were passed"]})
+        try:
+            user.alts.set(users)
+        except IntegrityError as err:
+            if err.__cause__.diag.constraint_name == 'api_useraltrelationship_prevent_alt_to_self':
+                raise ParseError(detail={
+                    "non_field_errors": ["The user may not be an alternate account of itself"]
+                })
+
+            raise
+
+        serializer = self.get_serializer(instance=user)
+        return Response(serializer.data, status=status.HTTP_200_OK)
+
     @action(detail=True)
     def metricity_data(self, request: Request, pk: str | None = None) -> Response:
         """Request handler for metricity_data endpoint."""