From 5b7be585ad96ab8127716c3c2114c0ea913dc1bd Mon Sep 17 00:00:00 2001
From: Eddie Maldonado <emaldonado@mbta.com>
Date: Thu, 26 Oct 2023 15:50:15 -0400
Subject: [PATCH] refactor: use PubSub for Realtime.Server

---
 lib/realtime/server.ex     | 41 ++++++++++++++++++--------------------
 lib/realtime/supervisor.ex |  1 +
 2 files changed, 20 insertions(+), 22 deletions(-)

diff --git a/lib/realtime/server.ex b/lib/realtime/server.ex
index 443757ef9c..fa749faa26 100644
--- a/lib/realtime/server.ex
+++ b/lib/realtime/server.ex
@@ -81,6 +81,9 @@ defmodule Realtime.Server do
   @spec default_name() :: GenServer.name()
   def default_name(), do: Realtime.Server
 
+  @spec pubsub_name() :: Phoenix.PubSub.t()
+  def pubsub_name(), do: Realtime.PubSub
+
   @spec start_link(Keyword.t()) :: GenServer.on_start()
   def start_link(start_link_opts) do
     GenServer.start_link(__MODULE__, [], start_link_opts)
@@ -210,17 +213,20 @@ defmodule Realtime.Server do
   @spec subscribe(GenServer.server(), {:run_ids, [Run.id()]}) :: [VehicleOrGhost.t()]
   @spec subscribe(GenServer.server(), {:block_ids, [Block.id()]}) :: [VehicleOrGhost.t()]
   @spec subscribe(GenServer.server(), {:alerts, Route.id()}) :: [String.t()]
+  defp subscribe(server, {:alerts, _route_id} = subscription_key) do
+    {pubsub, ets} = GenServer.call(server, :subscription_info)
+    Phoenix.PubSub.subscribe(pubsub, "realtime_alerts")
+    lookup({ets, subscription_key})
+  end
+
   defp subscribe(server, subscription_key) do
-    {registry_key, ets} = GenServer.call(server, :subscription_info)
-    Registry.register(Realtime.Registry, registry_key, subscription_key)
+    {pubsub, ets} = GenServer.call(server, :subscription_info)
+    Phoenix.PubSub.subscribe(pubsub, "realtime_vehicles")
     lookup({ets, subscription_key})
   end
 
   defp update_subscription(server, {:limited_search, _search_params} = subscription_key) do
-    {registry_key, ets} = GenServer.call(server, :subscription_info)
-    # Replace the old search subscription with the new one
-    Registry.unregister_match(Realtime.Registry, registry_key, {:limited_search, %{}})
-    Registry.register(Realtime.Registry, registry_key, subscription_key)
+    {_pubsub, ets} = GenServer.call(server, :subscription_info)
 
     lookup({ets, subscription_key})
   end
@@ -401,8 +407,7 @@ defmodule Realtime.Server do
 
   @impl true
   def handle_call(:subscription_info, _from, %__MODULE__{} = state) do
-    registry_key = self()
-    {:reply, {registry_key, state.ets}, state}
+    {:reply, {pubsub_name(), state.ets}, state}
   end
 
   def handle_call(:ets, _from, %__MODULE__{ets: ets} = state) do
@@ -541,21 +546,13 @@ defmodule Realtime.Server do
 
   @spec broadcast(t(), :vehicles | :alerts) :: :ok
   defp broadcast(state, data_type) do
-    registry_key = self()
-
-    Registry.dispatch(Realtime.Supervisor.registry_name(), registry_key, fn entries ->
-      Enum.each(entries, fn {pid, subscripition_key} ->
-        if (data_type == :alerts and match?({:alerts, _}, subscripition_key)) or
-             (data_type == :vehicles and !match?({:alerts, _}, subscripition_key)) do
-          send_data(pid, state)
-        end
-      end)
-    end)
-  end
+    topic =
+      case data_type do
+        :vehicles -> "realtime_vehicles"
+        :alerts -> "realtime_alerts"
+      end
 
-  @spec send_data(pid, t) :: broadcast_message
-  defp send_data(pid, state) do
-    send(pid, {:new_realtime_data, state.ets})
+    Phoenix.PubSub.broadcast(pubsub_name(), topic, {:new_realtime_data, state.ets})
   end
 
   @spec block_is_active?(VehicleOrGhost.t()) :: boolean
diff --git a/lib/realtime/supervisor.ex b/lib/realtime/supervisor.ex
index 5da03874c1..646057ea71 100644
--- a/lib/realtime/supervisor.ex
+++ b/lib/realtime/supervisor.ex
@@ -13,6 +13,7 @@ defmodule Realtime.Supervisor do
     children = [
       {Registry, keys: :duplicate, name: registry_name()},
       {Realtime.BlockWaiverStore, name: Realtime.BlockWaiverStore.default_name()},
+      {Phoenix.PubSub, name: Realtime.Server.pubsub_name()},
       {Realtime.Server, name: Realtime.Server.default_name()},
       {Realtime.TrainVehiclesPubSub, name: Realtime.TrainVehiclesPubSub.default_name()},
       {Realtime.DataStatusPubSub, name: Realtime.DataStatusPubSub.default_name()},