billscroll should now remember user's position across devices

src/apps/drama/models.py

@@ -83,6 +83,25 @@ class GameEvent(models.Model):
         return f"[{self.timestamp:%Y-%m-%d %H:%M}] {actor} → {self.verb}"
 
 
+class ScrollPosition(models.Model):
+    user = models.ForeignKey(
+        settings.AUTH_USER_MODEL, on_delete=models.CASCADE,
+        related_name="scroll_positions",
+    )
+    room = models.ForeignKey(
+        "epic.Room", on_delete=models.CASCADE,
+        related_name="scroll_positions",
+    )
+    position = models.PositiveIntegerField(default=0)
+    updated_at = models.DateTimeField(auto_now=True)
+
+    class Meta:
+        unique_together = [("user", "room")]
+
+    def __str__(self):
+        return f"{self.user.email} @ {self.room.name}: {self.position}px"
+
+
 def record(room, verb, actor=None, **data):
     """Record a game event in the drama log."""
     return GameEvent.objects.create(room=room, actor=actor, verb=verb, data=data)

src/apps/drama/tests/unit/test_models.py

@@ -1,6 +1,7 @@
 from django.test import TestCase
+from django.db import IntegrityError
 
-from apps.drama.models import GameEvent, record
+from apps.drama.models import GameEvent, ScrollPosition, record
 from apps.epic.models import Room
 from apps.lyric.models import User
 
@@ -42,3 +43,31 @@ class GameEventModelTest(TestCase):
     def test_str_without_actor_shows_system(self):
         event = record(self.room, GameEvent.ROLES_REVEALED)
         self.assertIn("system", str(event))
+
+
+class ScrollPositionModelTest(TestCase):
+    def setUp(self):
+        self.user = User.objects.create(email="reader@test.io")
+        self.room = Room.objects.create(name="Test Room", owner=self.user)
+
+    def test_can_save_scroll_position(self):
+        sp = ScrollPosition.objects.create(user=self.user, room=self.room, position=150)
+        self.assertEqual(ScrollPosition.objects.count(), 1)
+        self.assertEqual(sp.position, 150)
+
+    def test_default_position_is_zero(self):
+        sp = ScrollPosition.objects.create(user=self.user, room=self.room)
+        self.assertEqual(sp.position, 0)
+
+    def test_unique_per_user_and_room(self):
+        ScrollPosition.objects.create(user=self.user, room=self.room, position=50)
+        with self.assertRaises(IntegrityError):
+            ScrollPosition.objects.create(user=self.user, room=self.room, position=100)
+
+    def test_upsert_updates_existing_position(self):
+        ScrollPosition.objects.create(user=self.user, room=self.room, position=50)
+        ScrollPosition.objects.update_or_create(
+            user=self.user, room=self.room,
+            defaults={"position": 200},
+        )
+        self.assertEqual(ScrollPosition.objects.get(user=self.user, room=self.room).position, 200)