defmodule ProgressBar.AnimationServer do
  use GenServer

  @name :animation_server

  # Client API

  def start(config) do
    GenServer.start(__MODULE__, {config, 0}, name: @name)
  end

  def stop do
    GenServer.call(@name, :stop)
  end

  # GenServer API

  def init(state) do
    {:ok, tick(state)}
  end

  def handle_info(:tick, state) do
    {:noreply, tick(state)}
  end

  def handle_call(:stop, _from, {config, count}) do
    config[:render_done].()
    {:stop, :normal, :ok, {config, count}}
  end

  # Private

  defp tick({config, count}) do
    config[:render_frame].(count)

    # This timer is automatically cancelled when the server goes away.
    interval = config[:interval]
    Process.send_after(self, :tick, interval)

    {config, count + 1}
  end
end