Code for step 2

config/config.exs

@@ -0,0 +1,7 @@
+import Config
+
+config :payments_client, RateLimiter,
+  rate_limiter: PaymentsClient.RateLimiters.LeakyBucket,
+  timeframe_max_requests: 60,
+  timeframe_units: :seconds,
+  timeframe: 60

lib/payments_client/application.ex

@@ -5,10 +5,17 @@ defmodule PaymentsClient.Application do
 
   use Application
 
+  alias PaymentsClient.RateLimiter
+
   def start(_type, _args) do
     children = [
-      # Starts a worker by calling: PaymentsClient.Worker.start_link(arg)
-      # {PaymentsClient.Worker, arg}
+      {Task.Supervisor, name: RateLimiter.TaskSupervisor},
+      {RateLimiter.get_rate_limiter(),
+       %{
+         timeframe_max_requests: RateLimiter.get_requests_per_timeframe(),
+         timeframe_units: RateLimiter.get_timeframe_unit(),
+         timeframe: RateLimiter.get_timeframe()
+       }}
     ]
 
     # See https://hexdocs.pm/elixir/Supervisor.html

lib/rate_limiter.ex

@@ -0,0 +1,27 @@
+defmodule PaymentsClient.RateLimiter do
+  @callback make_request(request_handler :: tuple(), response_handler :: tuple()) :: :ok
+
+  def make_request(request_handler, response_handler) do
+    get_rate_limiter().make_request(request_handler, response_handler)
+  end
+
+  def get_rate_limiter, do: get_rate_limiter_config(:rate_limiter)
+  def get_requests_per_timeframe, do: get_rate_limiter_config(:timeframe_max_requests)
+  def get_timeframe_unit, do: get_rate_limiter_config(:timeframe_units)
+  def get_timeframe, do: get_rate_limiter_config(:timeframe)
+
+  def calculate_refresh_rate(num_requests, time, timeframe_units) do
+    floor(convert_time_to_milliseconds(timeframe_units, time) / num_requests)
+  end
+
+  def convert_time_to_milliseconds(:hours, time), do: :timer.hours(time)
+  def convert_time_to_milliseconds(:minutes, time), do: :timer.minutes(time)
+  def convert_time_to_milliseconds(:seconds, time), do: :timer.seconds(time)
+  def convert_time_to_milliseconds(:milliseconds, milliseconds), do: milliseconds
+
+  defp get_rate_limiter_config(config) do
+    :payments_client
+    |> Application.get_env(RateLimiter)
+    |> Keyword.get(config)
+  end
+end