From 6f88363d2fcbdc0e8bef77b9b12ed6792aa19f96 Mon Sep 17 00:00:00 2001
From: sloane <git@sloanelybutsurely.com>
Date: Mon, 19 Aug 2024 10:43:34 -0400
Subject: [PATCH] feat: cache routes by id to speed up alerts filtering (#2142)

* feat: cache routes

* feat: use route cache in alerts filter expansion
---
 config/config.exs                  |  1 +
 config/test.exs                    |  3 ++-
 lib/screens/alerts/cache/filter.ex |  7 +++---
 lib/screens/application.ex         |  3 ++-
 lib/screens/routes/routes_cache.ex | 39 ++++++++++++++++++++++++++++++
 5 files changed, 47 insertions(+), 6 deletions(-)
 create mode 100644 lib/screens/routes/routes_cache.ex

diff --git a/config/config.exs b/config/config.exs
index 762e36f1f..080d2aa16 100644
--- a/config/config.exs
+++ b/config/config.exs
@@ -486,6 +486,7 @@ config :screens, Screens.ScreenApiResponseCache,
   allocated_memory: 250_000_000
 
 config :screens, Screens.Stops.StopsToRoutes, adapter: Nebulex.Adapters.Local
+config :screens, Screens.Routes.RoutesCache, adapter: Nebulex.Adapters.Local
 
 # Import environment specific config. This must remain at the bottom
 # of this file so it overrides the configuration defined above.
diff --git a/config/test.exs b/config/test.exs
index 31ccf79b9..01855c5c4 100644
--- a/config/test.exs
+++ b/config/test.exs
@@ -27,7 +27,7 @@ config :screens,
   blue_bikes_station_status_url: [:no_api_requests_allowed_during_testing],
   blue_bikes_api_client: Screens.BlueBikes.FakeClient,
   stops_to_routes_route_mod: Screens.Routes.Route.Mock,
-  alerts_cache_filter_route_mod: Screens.Routes.Route.Mock,
+  routes_cache_route_mod: Screens.Routes.Route.Mock,
   dup_headsign_replacements: %{
     "Test 1" => "T1"
   },
@@ -164,3 +164,4 @@ config :screens, :screens_by_alert,
   screens_ttl_seconds: 1
 
 config :screens, Screens.Stops.StopsToRoutes, adapter: Nebulex.Adapters.Nil
+config :screens, Screens.Routes.RoutesCache, adapter: Nebulex.Adapters.Nil
diff --git a/lib/screens/alerts/cache/filter.ex b/lib/screens/alerts/cache/filter.ex
index 40ee875aa..e496bab78 100644
--- a/lib/screens/alerts/cache/filter.ex
+++ b/lib/screens/alerts/cache/filter.ex
@@ -3,11 +3,10 @@ defmodule Screens.Alerts.Cache.Filter do
   Logic to apply filters to a list of `Screens.Alerts.Alert` structs.
   """
   alias Screens.Routes.Route
+  alias Screens.Routes.RoutesCache
   alias Screens.RouteType
   alias Screens.Stops.StopsToRoutes
 
-  @route_mod Application.compile_env(:screens, :alerts_cache_filter_route_mod, Route)
-
   @default_activities ~w[BOARD EXIT RIDE]
 
   @type filter_opts() :: %{
@@ -127,8 +126,8 @@ defmodule Screens.Alerts.Cache.Filter do
   end
 
   defp matchers_for_route_id(route_id) do
-    case @route_mod.by_id(route_id) do
-      {:ok, %Route{type: type}} ->
+    case RoutesCache.by_id(route_id) do
+      %Route{type: type} ->
         [
           %{
             route_type: RouteType.to_id(type),
diff --git a/lib/screens/application.ex b/lib/screens/application.ex
index 3630957d9..2fdf4841b 100644
--- a/lib/screens/application.ex
+++ b/lib/screens/application.ex
@@ -38,7 +38,8 @@ defmodule Screens.Application do
       {Screens.OlCrowding.Agent, %{}},
       {Screens.ScreenApiResponseCache, []},
       Screens.Streams.Alerts,
-      Screens.Stops.StopsToRoutes
+      Screens.Stops.StopsToRoutes,
+      Screens.Routes.RoutesCache
     ]
 
     # See https://hexdocs.pm/elixir/Supervisor.html
diff --git a/lib/screens/routes/routes_cache.ex b/lib/screens/routes/routes_cache.ex
new file mode 100644
index 000000000..0222319b9
--- /dev/null
+++ b/lib/screens/routes/routes_cache.ex
@@ -0,0 +1,39 @@
+defmodule Screens.Routes.RoutesCache do
+  @moduledoc """
+  A read-through cache of routes by ID.
+  """
+  use Nebulex.Cache,
+    otp_app: :screens,
+    adapter: Application.compile_env(:screens, [__MODULE__, :adapter])
+
+  alias Screens.Routes.Route
+
+  @route_mod Application.compile_env(:screens, :routes_cache_route_mod, Screens.Routes.Route)
+
+  @base_ttl :timer.hours(1)
+
+  @spec by_id(id :: String.t()) :: Route.t() | nil
+  def by_id(id) do
+    if route = get(id) do
+      route
+    else
+      route = fetch_by_id(id)
+
+      unless is_nil(route), do: put(id, route, ttl: ttl())
+
+      route
+    end
+  end
+
+  defp fetch_by_id(id) do
+    case @route_mod.by_id(id) do
+      {:ok, %Route{} = route} -> route
+      _ -> nil
+    end
+  end
+
+  def ttl do
+    additional_minutes = :rand.uniform(30)
+    @base_ttl + :timer.minutes(additional_minutes)
+  end
+end