Add forward extremities to rooms

lib/matrix_server/room.ex

@@ -2,13 +2,15 @@ defmodule MatrixServer.Room do
   use Ecto.Schema
 
   import Ecto.Changeset
+  import Ecto.Query
 
-  alias MatrixServer.{Room, Event}
+  alias MatrixServer.{Repo, Room, Event}
   alias MatrixServerWeb.API.CreateRoom
 
   @primary_key {:id, :string, []}
   schema "rooms" do
     field :visibility, Ecto.Enum, values: [:public, :private]
+    field :forward_extremities, {:array, :string}
     has_many :events, Event, foreign_key: :event_id
   end
 
@@ -27,4 +29,23 @@ defmodule MatrixServer.Room do
   def generate_room_id do
     "!" <> MatrixServer.random_string(18) <> "@" <> MatrixServer.server_name()
   end
+
+  def update_forward_extremities(%Event{
+        event_id: event_id,
+        prev_events: prev_event_ids,
+        room_id: room_id
+      }) do
+    %Room{forward_extremities: forward_extremities} =
+      Room
+      |> where([r], r.id == ^room_id)
+      |> Repo.one!()
+
+    new_forward_extremities = [event_id | forward_extremities -- prev_event_ids]
+
+    {_, [room | _]} =
+      from(r in Room, where: r.id == ^room_id, select: r)
+      |> Repo.update_all(set: [forward_extremities: new_forward_extremities])
+
+    room
+  end
 end