Move constants to config, update string formatting

Not sure if this is the Elixir-y way to do this, but seems more logical
than hardcoding values such as redis connection.

Also went through and improved how string formatting was performed
throughout the app. Rather than "combining" <> "strings" this way, I'm
now just doing "#${variable}#{formatting}", which looks a lot cleaner.

config/config.exs

@@ -0,0 +1,7 @@
+import Config 
+
+config :privacy_revolver,
+  redis_conn: "redis://localhost:6379",
+  fallback_str: "-fallback",
+  update_file: ".update-results",
+  services_json: "services.json"

lib/privacy_revolver/application.ex

@@ -1,4 +1,5 @@
 defmodule PrivacyRevolver.Application do
+  @redis_conn Application.fetch_env!(:privacy_revolver, :redis_conn)
   @moduledoc false
 
   use Application
@@ -7,7 +8,7 @@ defmodule PrivacyRevolver.Application do
   def start(_type, _args) do
     children = [
       Plug.Cowboy.child_spec(scheme: :http, plug: PrivacyRevolver.Router, options: [port: 4001]),
-      {Redix, {"redis://localhost:6379", [name: :redix]}}
+      {Redix, {@redis_conn, [name: :redix]}}
     ]
 
     opts = [strategy: :one_for_one, name: PrivacyRevolver.Supervisor]

lib/privacy_revolver/router.ex

@@ -1,9 +1,15 @@
 defmodule PrivacyRevolver.Router do
+  @fallback_str Application.fetch_env!(:privacy_revolver, :fallback_str)
+
   use Plug.Router
 
   plug :match
   plug :dispatch
 
+  get "/" do
+    send_resp(conn, 200, "")
+  end
+
   get "/ping" do
     # Useful for app healthcheck
     {:ok, resp} = Redix.command(:redix, ["PING"])
@@ -11,19 +17,30 @@ defmodule PrivacyRevolver.Router do
   end
 
   get "/:service/*glob" do
-    full_path = "/" <> Enum.join(glob, "/")
-    {:ok, instances} = Redix.command(:redix, ["LRANGE", service, "0", "-1"])
+    path = Enum.join(glob, "/")
+    {:ok, instances} = Redix.command(
+      :redix,
+      ["LRANGE", service, "0", "-1"]
+    )
 
-    # Either pick a random available instance, or fall back to the default one
+    # Either pick a random available instance, 
+    # or fall back to the default one
     instance = if Enum.count(instances) > 0 do
       Enum.random(instances)
     else
-      Redix.command(:redix, ["GET", service <> "-fallback"])
+      {:ok, result} = Redix.command(
+        :redix,
+        ["GET", "#{service}#{@fallback_str}"]
+      )
+      result
     end
 
     # Redirect to the available instance
     conn |>
     Plug.Conn.resp(:found, "") |>
-    Plug.Conn.put_resp_header("location", instance <> full_path)
+    Plug.Conn.put_resp_header(
+      "location",
+      "#{instance}/#{path}"
+    )
   end
 end

update.exs

@@ -8,6 +8,15 @@ defmodule Service do
 end
 
 defmodule Instances do
+  @fallback_str Application.fetch_env!(:privacy_revolver, :fallback_str)
+  @update_file Application.fetch_env!(:privacy_revolver, :update_file)
+  @services_json Application.fetch_env!(:privacy_revolver, :services_json)
+
+  def init() do
+    File.rename(@update_file, "#{@update_file}-prev")
+    update(@services_json)
+  end
+
   def request(url) do
     case HTTPoison.get(url) do
       {:ok, %HTTPoison.Response{status_code: 200}} ->
@@ -19,10 +28,6 @@ defmodule Instances do
   end
 
   def update(filename) do
-    {:ok, conn} = Redix.start_link(
-      "redis://localhost:6379",
-      name: :redix
-    )
     {:ok, file} = File.read(filename)
     {:ok, json} = Poison.decode(file, as: [%Service{}])
 
@@ -32,20 +37,20 @@ defmodule Instances do
         request(instance_url <> service.test_url) == :good
       end)
 
-      add_to_redis(conn, service, result)
+      add_to_redis(service, result)
       log_results(service.type, result)
     end
   end
 
-  def add_to_redis(conn, service, instances) do
+  def add_to_redis(service, instances) do
     # Remove previous list of instances
-    Redix.command(conn, [
+    Redix.command(:redix, [
       "DEL",
       service.type
     ])
 
     # Update with new list of available instances
-    Redix.command(conn, [
+    Redix.command(:redix, [
       "LPUSH",
       service.type
     ] ++ instances)
@@ -53,26 +58,25 @@ defmodule Instances do
     # Set fallback to one of the available instances,
     # or the default instance if all are "down"
     if Enum.count(instances) > 0 do
-      Redix.command(conn, [
+      Redix.command(:redix, [
         "SET",
-        service.type <> "-fallback",
+        "#{service.type}#{@fallback_str}",
         Enum.random(instances)
       ])
     else
-      Redix.command(conn, [
+      Redix.command(:redix, [
         "SET",
-        service.type <> "-fallback",
+        "#{service.type}#{@fallback_str}",
         service.fallback
       ])
     end
   end
 
   def log_results(service_name, results) do
-    {:ok, file} = File.open(".update-results", [:append, {:delayed_write, 100, 20}])
-    IO.write(file, service_name <> ": " <> inspect(results) <> "\n")
+    {:ok, file} = File.open(@update_file, [:append, {:delayed_write, 100, 20}])
+    IO.write(file, "#{service_name}: #{inspect(results)}\n")
     File.close(file)
   end
 end
 
-File.rename(".update-results", ".update-results-prev")
-Instances.update("services.json")
+Instances.init()