rate_limit.ex

defmodule Sync.Middleware.RateLimit do
  @defaults [
    delay:        2000,
    max_retries:  5
  ]

  def call(env, next, opts) do
    opts        = opts || []
    delay       = Keyword.get(opts, :delay,       @defaults[:delay])
    max_retries = Keyword.get(opts, :max_retries, @defaults[:max_retries])

    retry(env, next, delay, max_retries)
  end

  defp retry(env, next, _delay, retries) when retries <= 1 do
    Tesla.run(env, next)
  end

  defp retry(env, next, delay, retries) do
    case Tesla.run(env, next) do
      %{status: 429} -> # rate limit exceeded
        :timer.sleep(delay)
        retry(env, next, delay, retries - 1)
        
      response -> response
    end
  end
end