enable last trip messages for red line

lib/signs/realtime.ex

@@ -209,21 +209,18 @@ defmodule Signs.Realtime do
   end
 
   defp has_service_ended_for_source?(sign, source, current_time) do
-    if source.headway_group not in ["red_trunk", "red_ashmont", "red_braintree"] do
+    num_last_trips =
       SourceConfig.sign_stop_ids(source)
-      |> Enum.count(&has_last_trip_departed_stop?(&1, sign, current_time)) >= 1
-    else
-      false
-    end
-  end
+      |> Stream.flat_map(&sign.last_trip_engine.get_recent_departures(&1))
+      |> Enum.count(fn {trip_id, departure_time} ->
+        # Use a 3 second buffer to make sure trips have fully departed
+        DateTime.to_unix(current_time) - DateTime.to_unix(departure_time) > 3 and
+          sign.last_trip_engine.is_last_trip?(trip_id)
+      end)
 
-  defp has_last_trip_departed_stop?(stop_id, sign, current_time) do
-    sign.last_trip_engine.get_recent_departures(stop_id)
-    |> Enum.any?(fn {trip_id, departure_time} ->
-      # Use a 3 second buffer to make sure trips have fully departed
-      DateTime.to_unix(current_time) - DateTime.to_unix(departure_time) > 3 and
-        sign.last_trip_engine.is_last_trip?(trip_id)
-    end)
+    # Red line trunk should wait for two last trips, one for each branch
+    threshold = if(source.headway_group == "red_trunk", do: 2, else: 1)
+    num_last_trips >= threshold
   end
 
   defp prediction_key(prediction) do

test/signs/realtime_test.exs

@@ -1767,6 +1767,28 @@ defmodule Signs.RealtimeTest do
 
       Signs.Realtime.handle_info(:run_loop, sign)
     end
+
+    test "Red line trunk service doesn't end after one last trip" do
+      expect_messages({"", ""})
+
+      Signs.Realtime.handle_info(:run_loop, %{
+        @sign
+        | source_config: %{@sign.source_config | headway_group: "red_trunk"}
+      })
+    end
+
+    test "Red line trunk service ends after two last trips" do
+      expect(Engine.LastTrip.Mock, :get_recent_departures, fn _ ->
+        %{"a" => ~U[2023-01-01 00:00:00.000Z], "b" => ~U[2023-01-01 00:00:00.000Z]}
+      end)
+
+      expect_messages({"Service ended", "No Southbound trains"})
+
+      Signs.Realtime.handle_info(:run_loop, %{
+        @sign
+        | source_config: %{@sign.source_config | headway_group: "red_trunk"}
+      })
+    end
   end
 
   describe "PA messages" do