filter system message on starting the chat

apps/chat/integrations/mattermost/client.py

@@ -156,6 +156,15 @@ class MattermostClient:
 
         return channel_id
 
+    @staticmethod
+    def _is_system_post(post: dict) -> bool:
+        """
+        Mattermost auto-generates posts like "user-x added to the channel"
+        (type e.g. "system_add_to_channel") whenever channel membership
+        changes. Real user-sent posts have an empty type.
+        """
+        return post.get("type", "").startswith("system_")
+
     def post_message(self, channel_id: str, message: str) -> str:
         """
         Post a message to the given channel using the admin token.
@@ -181,6 +190,8 @@ class MattermostClient:
     ) -> list[dict]:
         """
         Fetch posts from a channel and return them in chronological order.
+        System posts (channel membership changes, etc.) are excluded — only
+        real user-sent posts are returned.
 
         `since` is a Unix timestamp in **milliseconds**. When provided,
         `page` is ignored and all posts after that timestamp are returned.
@@ -200,19 +211,30 @@ class MattermostClient:
         posts_map: dict = data.get("posts", {})
 
         # Mattermost returns newest-first; reverse to get chronological order.
-        return [posts_map[pid] for pid in reversed(order) if pid in posts_map]
+        return [
+            posts_map[pid]
+            for pid in reversed(order)
+            if pid in posts_map and not self._is_system_post(posts_map[pid])
+        ]
 
     def get_latest_post_id(self, channel_id: str) -> str | None:
         """
-        Return the ID of the most recent post in the channel, or None if empty.
+        Return the ID of the most recent real (non-system) post in the
+        channel, or None if there are none yet.
         Used to derive `has_unread` against a stored last_read_mattermost_post_id.
         """
         try:
             data = self._driver.posts.get_posts_for_channel(
-                channel_id, params={"page": 0, "per_page": 1}
+                channel_id, params={"page": 0, "per_page": 20}
             )
         except Exception as exc:
             raise MattermostError(f"Fetching latest post failed: {exc}") from exc
 
         order: list[str] = data.get("order", [])
-        return order[0] if order else None
+        posts_map: dict = data.get("posts", {})
+
+        for pid in order:  # newest-first
+            post = posts_map.get(pid)
+            if post and not self._is_system_post(post):
+                return pid
+        return None

apps/chat/tests/test_mattermost_client.py

@@ -0,0 +1,77 @@
+from unittest.mock import Mock
+
+from apps.chat.integrations.mattermost.client import MattermostClient
+
+
+def _make_client(driver_response: dict) -> MattermostClient:
+    """Build a MattermostClient without hitting the network (no __init__)."""
+    client = MattermostClient.__new__(MattermostClient)
+    client._driver = Mock()
+    client._driver.posts.get_posts_for_channel.return_value = driver_response
+    return client
+
+
+def _post(post_id, msg="hi", post_type="", user_id="u1"):
+    return {
+        "id": post_id,
+        "type": post_type,
+        "message": msg,
+        "user_id": user_id,
+        "create_at": 1700000000000,
+    }
+
+
+def test_get_posts_excludes_system_posts():
+    # Mattermost order is newest-first.
+    posts_map = {
+        "p1": _post("p1", "real message"),
+        "sys1": _post("sys1", "user-x added to the channel", post_type="system_add_to_channel"),
+    }
+    client = _make_client({"order": ["sys1", "p1"], "posts": posts_map})
+
+    result = client.get_posts("chan-1")
+
+    assert [p["id"] for p in result] == ["p1"]
+
+
+def test_get_posts_keeps_chronological_order_with_no_system_posts():
+    posts_map = {
+        "p1": _post("p1", "first"),
+        "p2": _post("p2", "second"),
+    }
+    client = _make_client({"order": ["p2", "p1"], "posts": posts_map})
+
+    result = client.get_posts("chan-1")
+
+    assert [p["id"] for p in result] == ["p1", "p2"]
+
+
+def test_get_latest_post_id_skips_leading_system_post():
+    # sys1 is newest (e.g. someone was just added), p1 is the latest real message.
+    posts_map = {
+        "sys1": _post("sys1", "user-y added to the channel", post_type="system_add_to_channel"),
+        "p1": _post("p1", "real message"),
+    }
+    client = _make_client({"order": ["sys1", "p1"], "posts": posts_map})
+
+    assert client.get_latest_post_id("chan-1") == "p1"
+
+
+def test_get_latest_post_id_returns_none_when_only_system_posts_exist():
+    posts_map = {
+        "sys1": _post("sys1", "user-x added to the channel", post_type="system_add_to_channel"),
+        "sys2": _post("sys2", "user-y added to the channel", post_type="system_add_to_channel"),
+    }
+    client = _make_client({"order": ["sys2", "sys1"], "posts": posts_map})
+
+    assert client.get_latest_post_id("chan-1") is None
+
+
+def test_get_latest_post_id_returns_newest_real_post_when_no_system_posts():
+    posts_map = {
+        "p1": _post("p1", "first"),
+        "p2": _post("p2", "second"),
+    }
+    client = _make_client({"order": ["p2", "p1"], "posts": posts_map})
+
+    assert client.get_latest_post_id("chan-1") == "p2"