vt_gen_timer

defmodule GenTimer.Manager do
  use GenServer

  require Logger

  alias GenTimer.{Timer, Messenger}

  def child_spec({duration, topic}) do
    %{
      id: {__MODULE__, topic},
      start: {__MODULE__, :start_link, [{duration, topic}]},
      restart: :temporary
    }
  end

  def start_link({duration, topic}) do
    GenServer.start_link(
      __MODULE__,
      {duration, topic},
      name: via(topic)
    )
  end

  def initialize(duration, topic) do
    DynamicSupervisor.start_child(
      GenTimer.Supervisor.Manager,
      {__MODULE__, {duration, topic}}
    )
  end

  def start(topic) do
    GenServer.cast(via(topic), :start)
  end

  def get_timer(topic) do
    GenServer.call(via(topic), :get_timer)
  end

  def pause(topic) do
    GenServer.cast(via(topic), :pause)
  end

  def reset(topic) do
    GenServer.cast(via(topic), :reset)
  end

  @impl true
  def init({duration, topic}) do
    new_timer =
      duration
      |> Timer.new()
      |> Messenger.broadcast(topic)

    {:ok, {new_timer, topic}}
  end

  @impl true
  def handle_call(:get_timer, _from, {timer, _topic} = state) do
    {:reply, timer, state}
  end

  @impl true
  def handle_cast(:start, {timer, topic}) do
    started_timer =
      timer
      |> Timer.start()
      |> Messenger.tick()
      |> Messenger.broadcast(topic)

    {:noreply, {started_timer, topic}}
  end

  def handle_cast(:pause, {timer, topic}) do
    paused_timer =
      timer
      |> Timer.pause()
      |> Messenger.broadcast(topic)

    {:noreply, {paused_timer, topic}}
  end

  def handle_cast(:reset, {timer, topic}) do
    reset_timer =
      timer
      |> Timer.reset()
      |> Messenger.broadcast(topic)

    {:noreply, {reset_timer, topic}}
  end

  @impl true
  def handle_info(:tick, {timer, topic}) do
    ticking_timer =
      timer
      |> Timer.increment()
      |> Messenger.tick() 
      |> Messenger.broadcast(topic)

    if ticking_timer.state == :finished do
      {:stop, :shutdown, {ticking_timer, topic}}
    else
      {:noreply, {ticking_timer, topic}}
    end
  end

  def handle_info(_msg, {timer, topic}) do
    {:noreply, {timer, topic}}
  end

  def via(name) do
    {
      :via,
      Registry,
      {GenTimer.Registry.Manager, name}
    }
  end
end