chat implemented, testing needed

backend/social/chat/models.py

@@ -213,4 +213,24 @@ class MessageFile(SoftDeleteModel):
     uploaded_at = models.DateTimeField(auto_now_add=True)
 
     def __str__(self):
-        return f"Media {self.id} for Message {self.message.id}"
+        return f"Media {self.id} for Message {self.message.id}"
+
+
+class ChatReadStatus(models.Model):
+    user = models.ForeignKey(
+        settings.AUTH_USER_MODEL,
+        on_delete=models.CASCADE,
+        related_name='chat_read_statuses',
+    )
+    chat = models.ForeignKey(
+        Chat,
+        on_delete=models.CASCADE,
+        related_name='read_statuses',
+    )
+    last_read_at = models.DateTimeField(auto_now=True)
+
+    class Meta:
+        unique_together = ('user', 'chat')
+
+    def __str__(self):
+        return f"{self.user} read {self.chat} at {self.last_read_at}"