Draft implementation of Faye Client in Elixir

faye.ex

defmodule MyApp.Faye do
  @name __MODULE__
  @unconnected  1
  @connecting   2
  @connected    3
  @disconnected 4
  @handshake_params %{
    channel: "/meta/handshake",
    version: "1.0",
    supportedConnectionTypes: ["long-polling"]
  }
  @request_headers [{"Content-Type", "application/json"}]

  use HTTPoison.Base

  defmodule State do
    defstruct url: nil, state: @unconnected, client_id: nil
  end

  def start_link do
    faye_state = %State{url: Application.get_env(:faye, :url)}
    Agent.start_link(fn -> faye_state end, name: @name)
    handshake
    {:ok, self}
  end

  def publish(channel, params) do
    spawn fn ->
      if Agent.get(@name, fn faye -> faye.url end) != @connected do
        handshake
      end
      send %{
        "channel" => channel, 
        "data" => params, 
        "clientId" => Agent.get(@name, fn faye -> faye.client_id end)
      }
    end
  end

  defp handshake do
    Agent.update(@name, &(%{&1 | :state => @connecting}))
    case send(@handshake_params) do
      {:ok, %HTTPoison.Response{body: body}} ->
        [data|_] = Poison.decode!(body)
        Agent.update(@name, &(%{&1 | :client_id => Dict.get(data, "clientId")}))
        Agent.update(@name, &(%{&1 | :state => @connected}))
      {:error, _} ->
        IO.puts("Handshake failed. Retry in 10 seconds")
        Agent.update(@name, &(%{&1 | :state => @unconnected}))
        :timer.sleep(10000)
        handshake
    end
  end

  defp send(params) do
    post(Agent.get(@name, fn faye -> faye.url end),
           params |> to_json,
           @request_headers)
  end

  defp to_json(payload) do
    Poison.encode!(payload)
  end
end