Merge pull request #53 from mbta/ph-off-switch

feat: "Off switch" config in S3

lib/screens/application.ex

@@ -6,12 +6,15 @@ defmodule Screens.Application do
   use Application
 
   def start(_type, _args) do
+    import Supervisor.Spec, warn: false
+
     # List all child processes to be supervised
     children = [
       # Start the endpoint when the application starts
-      ScreensWeb.Endpoint
+      ScreensWeb.Endpoint,
       # Starts a worker by calling: Screens.Worker.start_link(arg)
       # {Screens.Worker, arg},
+      Screens.Override.Supervisor
     ]
 
     # See https://hexdocs.pm/elixir/Supervisor.html

lib/screens/override/fetch.ex

@@ -0,0 +1,31 @@
+defmodule Screens.Override.Fetch do
+  @moduledoc false
+
+  @default_opts [timeout: 2000, recv_timeout: 2000]
+
+  def fetch_config_from_s3(opts \\ []) do
+    url = "https://mbta-dotcom.s3.amazonaws.com/screens/config/" <> config_path_for_environment()
+    headers = []
+
+    with {:ok, response} <- HTTPoison.get(url, headers, Keyword.merge(@default_opts, opts)),
+         %{status_code: 200, body: body} <- response,
+         {:ok, parsed} <- Jason.decode(body),
+         %{"disabled_screen_ids" => disabled_screen_ids, "globally_disabled" => globally_disabled} <-
+           parsed do
+      {:ok,
+       %{
+         globally_disabled: globally_disabled,
+         disabled_screen_ids: MapSet.new(disabled_screen_ids)
+       }}
+    else
+      _ -> :error
+    end
+  end
+
+  defp config_path_for_environment do
+    case Application.get_env(:screens, :environment_name) do
+      "prod" -> "prod.json"
+      _ -> "dev.json"
+    end
+  end
+end

lib/screens/override/state.ex

@@ -0,0 +1,55 @@
+defmodule Screens.Override.State do
+  @moduledoc false
+
+  @initial_fetch_wait_ms 500
+  @refresh_ms 15 * 1000
+  @default_config %{globally_disabled: false, disabled_screen_ids: MapSet.new()}
+
+  use GenServer
+
+  def start_link(opts \\ []) do
+    GenServer.start_link(__MODULE__, :ok, opts)
+  end
+
+  def lookup(pid \\ __MODULE__, screen_id) do
+    GenServer.call(pid, {:lookup, screen_id})
+  end
+
+  def schedule_refresh(pid, ms \\ @refresh_ms) do
+    Process.send_after(pid, :refresh, ms)
+    :ok
+  end
+
+  ###
+
+  @impl true
+  def init(:ok) do
+    schedule_refresh(self(), @initial_fetch_wait_ms)
+    {:ok, @default_config}
+  end
+
+  @impl true
+  def handle_call({:lookup, _screen_id}, _from, %{globally_disabled: true} = state) do
+    {:reply, true, state}
+  end
+
+  def handle_call(
+        {:lookup, screen_id},
+        _from,
+        %{globally_disabled: false, disabled_screen_ids: disabled_screen_ids} = state
+      ) do
+    {:reply, MapSet.member?(disabled_screen_ids, screen_id), state}
+  end
+
+  @impl true
+  def handle_info(:refresh, _state) do
+    new_state =
+      case Screens.Override.Fetch.fetch_config_from_s3() do
+        {:ok, config} -> config
+        :error -> @default_config
+      end
+
+    schedule_refresh(self())
+    {:noreply, new_state}
+  end
+end

lib/screens/override/supervisor.ex

@@ -0,0 +1,17 @@
+defmodule Screens.Override.Supervisor do
+  @moduledoc false
+
+  use Supervisor
+
+  def start_link([]) do
+    Supervisor.start_link(__MODULE__, :ok, name: __MODULE__)
+  end
+
+  def init(:ok) do
+    children = [
+      worker(Screens.Override.State, [[name: Screens.Override.State]])
+    ]
+
+    supervise(children, strategy: :one_for_one)
+  end
+end

lib/screens/screen_data.ex

@@ -5,7 +5,18 @@ defmodule Screens.ScreenData do
   alias Screens.Departures.Departure
   alias Screens.NearbyConnections
 
-  def by_stop_id_with_version(stop_id, client_version) do
+  def by_stop_id_with_override_and_version(stop_id, screen_id, client_version) do
+    if Screens.Override.State.lookup(String.to_integer(screen_id)) do
+      %{
+        force_reload: false,
+        success: false
+      }
+    else
+      by_stop_id_with_version(stop_id, client_version)
+    end
+  end
+
+  defp by_stop_id_with_version(stop_id, client_version) do
     api_version = Application.get_env(:screens, :api_version)
 
     if api_version == client_version do

lib/screens_web/controllers/screen_api_controller.ex

@@ -7,7 +7,7 @@ defmodule ScreensWeb.ScreenApiController do
       |> Application.get_env(:screen_data)
       |> Map.get(screen_id)
       |> Map.get(:stop_id)
-      |> Screens.ScreenData.by_stop_id_with_version(version)
+      |> Screens.ScreenData.by_stop_id_with_override_and_version(screen_id, version)
 
     json(conn, data)
   end