fix: support separate alert status for top/bottom

different alert status per top/bottom config are needed to support
showing an alert status based message on a single source config. this is
most common when top and bottom source configs are for different
lines/routes.

previously the alert_status for a sign was reduced down to a single
value which could cause weird behavior when an alert was only effecting
one of the two source configs.

lib/signs/realtime.ex

@@ -142,12 +142,27 @@ defmodule Signs.Realtime do
   end
 
   def handle_info(:run_loop, sign) do
-    sign_stop_ids = SourceConfig.sign_stop_ids(sign.source_config)
-    sign_routes = SourceConfig.sign_routes(sign.source_config)
-    alert_status = sign.alerts_engine.max_stop_status(sign_stop_ids, sign_routes)
     sign_config = sign.config_engine.sign_config(sign.id)
     current_time = sign.current_time_fn.()
 
+    alert_status =
+      case sign.source_config do
+        {top, bottom} ->
+          top_alert_status = get_alert_status_for_source_config(top, sign.alerts_engine)
+          bottom_alert_status = get_alert_status_for_source_config(bottom, sign.alerts_engine)
+
+          {top_alert_status, bottom_alert_status}
+
+        source_config ->
+          alert_status = get_alert_status_for_source_config(source_config, sign.alerts_engine)
+
+          alert_status
+      end
+      |> then(fn
+        {alert_status, alert_status} -> alert_status
+        alert_status -> alert_status
+      end)
+
     first_scheduled_departures =
       case sign.source_config do
         {top, bottom} ->
@@ -160,8 +175,12 @@ defmodule Signs.Realtime do
           }
 
         source ->
-          {sign.headway_engine.get_first_scheduled_departure(sign_stop_ids),
-           source.headway_destination}
+          {
+            source
+            |> SourceConfig.sign_stop_ids()
+            |> sign.headway_engine.get_first_scheduled_departure(),
+            source.headway_destination
+          }
       end
 
     prev_predictions_lookup =
@@ -286,4 +305,12 @@ defmodule Signs.Realtime do
   def decrement_ticks(sign) do
     %{sign | tick_read: sign.tick_read - 1}
   end
+
+  defp get_alert_status_for_source_config(config, alerts_engine) do
+    stop_ids = SourceConfig.sign_stop_ids(config)
+    routes = SourceConfig.sign_routes(config)
+    alert_status = alerts_engine.max_stop_status(stop_ids, routes)
+
+    alert_status
+  end
 end

lib/signs/utilities/messages.ex

@@ -176,13 +176,41 @@ defmodule Signs.Utilities.Messages do
           :top | :bottom
         ) :: Signs.Realtime.line_content()
   defp get_paging_headway_or_alert_messages(
-         %Signs.Realtime{source_config: {top, bottom}} = sign,
+         %Signs.Realtime{source_config: {config, _bottom}} = sign,
+         current_time,
+         {alert_status, _},
+         :top
+       ) do
+    get_paging_alert_message(alert_status, sign.uses_shuttles, config.headway_destination) ||
+      Signs.Utilities.Headways.get_paging_message(sign, config, current_time)
+  end
+
+  defp get_paging_headway_or_alert_messages(
+         %Signs.Realtime{source_config: {_top, config}} = sign,
+         current_time,
+         {_, alert_status},
+         :bottom
+       ) do
+    get_paging_alert_message(alert_status, sign.uses_shuttles, config.headway_destination) ||
+      Signs.Utilities.Headways.get_paging_message(sign, config, current_time)
+  end
+
+  defp get_paging_headway_or_alert_messages(
+         %Signs.Realtime{source_config: {config, _bottom}} = sign,
          current_time,
          alert_status,
-         line
+         :top
        ) do
-    config = if(line == :top, do: top, else: bottom)
+    get_paging_alert_message(alert_status, sign.uses_shuttles, config.headway_destination) ||
+      Signs.Utilities.Headways.get_paging_message(sign, config, current_time)
+  end
 
+  defp get_paging_headway_or_alert_messages(
+         %Signs.Realtime{source_config: {_top, config}} = sign,
+         current_time,
+         alert_status,
+         :bottom
+       ) do
     get_paging_alert_message(alert_status, sign.uses_shuttles, config.headway_destination) ||
       Signs.Utilities.Headways.get_paging_message(sign, config, current_time)
   end