requester.ex

defmodule Wrench.Hex.Api.Requester do
  use GenServer
  require Logger

  @config Application.get_env(:wrench, __MODULE__)
  @api_key @config[:api_key]
  @ua "Wrench/#{Application.spec(:wrench, :vsn)} (contact #{Application.get_env(:wrench, :operator_contact)})"
  @endpoint "https://hex.pm/api"

  def start_link(opts) do
    GenServer.start_link(__MODULE__, opts)
  end

  @doc """
  ## Opts
  - make_request: Optional, mostly for testing.
      Should have same behavior as private fun `__MODULE__.make_request/1`
  """
  @impl true
  def init(opts) do
    {:ok,
     %{
       make_request: Keyword.get(opts, :make_request, &make_request/1),
       limit: %{
         remaining: 1,
         reset_time: nil
       }
     }}
  end

  @impl true
  def handle_call({:request, request}, _from, state) do
    unix_now = DateTime.utc_now() |> DateTime.to_unix()

    limit =
      if state.limit.remaining <= 0 do
        if state.limit.reset_time <= unix_now do
          # Give us one request to find the new limits
          %{state.limit | remaining: 1, reset_time: nil}
        else
          # TODO: How to wait until reset_time
        end
      else
        state.limit
      end

    if limit.remaining > 0 do
      with {:ok, reply, new_limit} <- make_request(request) do
        {:reply, reply, %{state | limit: new_limit}}
      end
    end
  end

  defp make_request(
         %{method: method, path: path, params: params, body: body, etag: etag} = request
       ) do
    Logger.info("Requesting #{inspect(request)}")

    headers = [{"Authorization", @api_key}, {"User-Agent", @ua}]

    headers =
      if is_nil(etag) do
        headers
      else
        [{"ETag", etag} | headers]
      end

    reply =
      Finch.build(
        method,
        "#{@endpoint}/#{path}?#{URI.encode_query(params, :rfc3986)}",
        headers,
        body
      )
      |> Finch.request(Wrench.Finch)

    with {:ok, %Finch.Response{headers: headers} = reply} <- reply do
      headers = Map.new(headers)
      remaining = headers["x-ratelimit-remaining"]
      reset = headers["x-ratelimit-reset"]

      {:ok, {reply, %{remaining: remaining, reset_time: reset}}}
    end
  end
end