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 +1,41 @@
+# Generated by Django 5.0 on 2023-12-14 13:14
+
+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')),
+                ('created_at', models.DateTimeField(auto_now_add=True)),
+                ('updated_at', models.DateTimeField(auto_now=True)),
+                ('context', models.TextField(help_text='The reason for why this account was associated as an alt.', max_length=1900)),
+                ('actor', models.ForeignKey(help_text='The moderator that associated these accounts together.', on_delete=django.db.models.deletion.CASCADE, related_name='+', to='api.user')),
+                ('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/migrations/0096_merge_0093_user_alts_0095_user_display_name.py

@@ -0,0 +1,14 @@
+# Generated by Django 5.0 on 2024-05-20 05:14
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('api', '0093_user_alts'),
+        ('api', '0095_user_display_name'),
+    ]
+
+    operations = [
+    ]

pydis_site/apps/api/models/__init__.py

@@ -19,5 +19,6 @@
     OffTopicChannelName,
     Reminder,
     Role,
-    User
+    User,
+    UserAltRelationship
 )

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

@@ -16,4 +16,4 @@
 from .offensive_message import OffensiveMessage
 from .reminder import Reminder
 from .role import Role
-from .user import User
+from .user import User, UserAltRelationship

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

@@ -4,7 +4,7 @@
 from django.db import models
 
 from pydis_site.apps.api.models.bot.role import Role
-from pydis_site.apps.api.models.mixins import ModelReprMixin
+from pydis_site.apps.api.models.mixins import ModelReprMixin, ModelTimestampMixin
 
 
 def _validate_existing_role(value: int) -> None:
@@ -66,6 +66,13 @@ class User(ModelReprMixin, models.Model):
         help_text="Whether this user is in our server.",
         verbose_name="In Guild"
     )
+    alts = models.ManyToManyField(
+        'self',
+        through='UserAltRelationship',
+        through_fields=('source', 'target'),
+        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."""
@@ -91,3 +98,45 @@ def username(self) -> str:
         For usability in read-only fields such as Django Admin.
         """
         return str(self)
+
+
+class UserAltRelationship(ModelReprMixin, ModelTimestampMixin, 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",
+    )
+    context = models.TextField(
+        help_text="The reason for why this account was associated as an alt.",
+        max_length=1900
+    )
+    actor = models.ForeignKey(
+        User,
+        on_delete=models.CASCADE,
+        related_name='+',
+        help_text="The moderator that associated these accounts together."
+    )
+
+    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

@@ -11,6 +11,7 @@
     ListSerializer,
     ModelSerializer,
     PrimaryKeyRelatedField,
+    SerializerMethodField,
     ValidationError
 )
 from rest_framework.settings import api_settings
@@ -35,7 +36,8 @@
     OffensiveMessage,
     Reminder,
     Role,
-    User
+    User,
+    UserAltRelationship
 )
 
 class FrozenFieldsMixin:
@@ -507,7 +509,7 @@ def to_representation(self, instance: Infraction) -> dict:
         """Return the dictionary representation of this infraction."""
         ret = super().to_representation(instance)
 
-        ret['user'] = UserSerializer(instance.user).data
+        ret['user'] = UserWithAltsSerializer(instance.user).data
         ret['actor'] = UserSerializer(instance.actor).data
 
         return ret
@@ -663,6 +665,36 @@ def update(self, queryset: QuerySet, validated_data: list) -> list:
         return updated
 
 
+class UserAltRelationshipSerializer(FrozenFieldsMixin, ModelSerializer):
+    """A class providing (de-)serialization of `UserAltRelationship` instances."""
+
+    actor = PrimaryKeyRelatedField(queryset=User.objects.all())
+    source = PrimaryKeyRelatedField(queryset=User.objects.all())
+    target = PrimaryKeyRelatedField(queryset=User.objects.all())
+
+    class Meta:
+        """Metadata defined for the Django REST Framework."""
+
+        model = UserAltRelationship
+        fields = ('source', 'target', 'actor', 'context', 'created_at', 'updated_at')
+        frozen_fields = ('source', 'target', 'actor')
+        depth = 1
+
+    def to_representation(self, instance: UserAltRelationship) -> dict:
+        """Add the alts of the target to the representation."""
+        representation = super().to_representation(instance)
+        representation['alts'] = tuple(
+            user_id
+            for (user_id,) in (
+                UserAltRelationship.objects
+                .filter(source=instance.target)
+                .values_list('target_id')
+            )
+        )
+        return representation
+
+
+
 class UserSerializer(ModelSerializer):
     """A class providing (de-)serialization of `User` instances."""
 
@@ -685,6 +717,26 @@ def create(self, validated_data: dict) -> User:
             raise ValidationError({"id": ["User with ID already present."]})
 
 
+class UserWithAltsSerializer(FrozenFieldsMixin, UserSerializer):
+    """A class providing (de-)serialization of `User` instances, expanding their alternate accounts."""
+
+    alts = SerializerMethodField()
+
+    class Meta:
+        """Metadata defined for the Django REST Framework."""
+
+        model = User
+        fields = ('id', 'name', 'display_name', 'discriminator', 'roles', 'in_guild', 'alts')
+        frozen_fields = ('alts',)
+
+    def get_alts(self, user: User) -> list[dict]:
+        """Retrieve the alts with all additional data on them."""
+        return [
+            UserAltRelationshipSerializer(alt).data
+            for alt in user.alts.through.objects.filter(source=user)
+        ]
+
+
 class NominationEntrySerializer(ModelSerializer):
     """A class providing (de-)serialization of `NominationEntry` instances."""
 

pydis_site/apps/api/tests/test_infractions.py

@@ -749,6 +749,8 @@ def check_expanded_fields(self, infraction):
             obj = infraction[key]
             for field in ('id', 'name', 'discriminator', 'roles', 'in_guild'):
                 self.assertTrue(field in obj, msg=f'field "{field}" missing from {key}')
+            if key == 'user':
+                self.assertIn('alts', obj)
 
     def test_list_expanded(self):
         url = reverse('api:bot:infraction-list-expanded')