From a501f8bb07dff8078109a744c2f0bf6250fe3edb Mon Sep 17 00:00:00 2001
From: Paul Swartz <paul@paulswartz.net>
Date: Wed, 20 Sep 2023 09:29:27 -0400
Subject: [PATCH] feat: make MqttMediator config separate from the SOURCE
 envvar

This allows us to add new environment variables for the MQTT broker,
without breaking existing API instances which expect the source to be an
HTTPS URL.
---
 apps/state_mediator/config/config.exs         |  2 ++
 apps/state_mediator/lib/state_mediator.ex     | 33 +++++++------------
 .../lib/state_mediator/mqtt_mediator.ex       |  2 +-
 .../state_mediator/mqtt_mediator_test.exs     |  3 +-
 4 files changed, 16 insertions(+), 24 deletions(-)

diff --git a/apps/state_mediator/config/config.exs b/apps/state_mediator/config/config.exs
index a4b5d42fd..82ec1db00 100644
--- a/apps/state_mediator/config/config.exs
+++ b/apps/state_mediator/config/config.exs
@@ -29,6 +29,8 @@ config :state_mediator, State.Vehicle,
     "MBTA_VEHICLE_SOURCE",
     "https://cdn.mbta.com/realtime/VehiclePositions_enhanced.json"
   },
+  broker: {:system, "MBTA_VEHICLE_BROKER", nil},
+  topic: {:system, "MBTA_VEHICLE_TOPIC", nil},
   username: {:system, "MBTA_VEHICLE_USERNAME", nil},
   password: {:system, "MBTA_VEHICLE_PASSWORD", nil}
 
diff --git a/apps/state_mediator/lib/state_mediator.ex b/apps/state_mediator/lib/state_mediator.ex
index f1efc3f69..6d2e55147 100644
--- a/apps/state_mediator/lib/state_mediator.ex
+++ b/apps/state_mediator/lib/state_mediator.ex
@@ -36,7 +36,7 @@ defmodule StateMediator do
           interval: 10_000
         ]
       },
-      vehicle_mediator_child(source_url(State.Vehicle)),
+      vehicle_mediator_child(app_value(State.Vehicle, :broker), source_url(State.Vehicle)),
       {
         StateMediator.Mediator,
         [
@@ -65,46 +65,35 @@ defmodule StateMediator do
     []
   end
 
-  defp vehicle_mediator_child("mqtt" <> _ = url) do
+  defp vehicle_mediator_child(no_broker, url) when no_broker in ["", nil] do
     {
-      StateMediator.MqttMediator,
+      StateMediator.Mediator,
       [
         spec_id: :vehicle_mediator,
         state: State.Vehicle,
         url: url,
-        username: app_value(State.Vehicle, :username),
-        password: app_value(State.Vehicle, :password),
-        sync_timeout: 30_000
+        opts: [timeout: 10_000],
+        sync_timeout: 30_000,
+        interval: 1_000
       ]
     }
   end
 
-  defp vehicle_mediator_child(["mqtt" <> _ | _] = url) do
+  defp vehicle_mediator_child(broker, _url) do
     {
       StateMediator.MqttMediator,
       [
         spec_id: :vehicle_mediator,
         state: State.Vehicle,
-        url: url,
+        url: broker,
+        topic: app_value(State.Vehicle, :topic),
+        username: app_value(State.Vehicle, :username),
+        password: app_value(State.Vehicle, :password),
         sync_timeout: 30_000
       ]
     }
   end
 
-  defp vehicle_mediator_child(url) do
-    {
-      StateMediator.Mediator,
-      [
-        spec_id: :vehicle_mediator,
-        state: State.Vehicle,
-        url: url,
-        opts: [timeout: 10_000],
-        sync_timeout: 30_000,
-        interval: 1_000
-      ]
-    }
-  end
-
   @spec crowding_children(boolean()) :: [:supervisor.child_spec() | {module(), term()} | module()]
   defp crowding_children(true) do
     Logger.info("#{__MODULE__} CR_CROWDING_ENABLED=true")
diff --git a/apps/state_mediator/lib/state_mediator/mqtt_mediator.ex b/apps/state_mediator/lib/state_mediator/mqtt_mediator.ex
index c543da4d0..ba4fd1e6f 100644
--- a/apps/state_mediator/lib/state_mediator/mqtt_mediator.ex
+++ b/apps/state_mediator/lib/state_mediator/mqtt_mediator.ex
@@ -50,7 +50,7 @@ defmodule StateMediator.MqttMediator do
     url = Keyword.fetch!(options, :url)
     configs = configs_from_url(url, options)
 
-    "/" <> topic = URI.decode_www_form(URI.parse(url).path)
+    topic = Keyword.fetch!(options, :topic)
 
     sync_timeout = options |> Keyword.get(:sync_timeout, 5000)
 
diff --git a/apps/state_mediator/test/state_mediator/mqtt_mediator_test.exs b/apps/state_mediator/test/state_mediator/mqtt_mediator_test.exs
index 2f6138ff5..810d243cb 100644
--- a/apps/state_mediator/test/state_mediator/mqtt_mediator_test.exs
+++ b/apps/state_mediator/test/state_mediator/mqtt_mediator_test.exs
@@ -28,7 +28,8 @@ defmodule StateMediator.MqttMediatorTest do
 
   # @moduletag capture_log: true
   @opts [
-    url: "mqtt://test.mosquitto.org/#{URI.encode_www_form("home/#")}",
+    url: "mqtt://test.mosquitto.org",
+    topic: "home/#",
     state: __MODULE__.StateModule
   ]