defmodule ExWechat.TokenServ do
  @moduledoc """
  Token Service
  """

  use GenServer
  import ExWechat.Util

  @interval 600

  def start_link(opts \\ []) do
    GenServer.start_link(__MODULE__, :ok, opts)
  end


  @doc """
  The Lastest Token
  """
  def token, do: GenServer.call(__MODULE__, :token)


  # ------------------------------------------------------------
  # Callback
  # ------------------------------------------------------------
  def init(:ok) do
    {:ok, %{id: ExWechat.app_id(), secret: ExWechat.app_secret(), updated: nil, token: nil}, 0}
  end

  def handle_info(:timeout, state) do
    {:noreply, %{state | updated: now, token: access_token(state.id, state.secret)}, @interval * 1000}
  end


  def handle_call(:token, _from, state) do
    timeout = round(@interval - (now - state.updated)) * 1000
    {:reply, state.token, state, timeout}
  end



  # ------------------------------------------------------------
  # Private
  # ------------------------------------------------------------
  defp access_token(appId, appSecret) do
    {:ok, resp} = HTTPoison.get(
            ~s"https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=#{appId}&secret=#{appSecret}",
            %{},
            ["content-type": "application/json"]
          )
    {:ok, json} = Poison.decode(resp.body)

    json |> Map.get("access_token")
  end
end