Elixir Pomodoro Timer

pomodoro.ex

defmodule Pomodoro do
  @moduledoc """
  Adapted from the Countdown module
  in 'Programming Elixir' by Dave Thomas.
  
  # Usage:
  
      $ iex pomodoro.ex
      
      iex> Pomodoro.start(15, 5, true)

  """

  defp sleep(seconds) do
    receive do
      after seconds * 1000 -> nil
    end
  end

  def say(text) do
    spawn fn -> :os.cmd('say #{text}') end
  end

  defp announce_time(count, every) do
    case rem(count, every) do
      0 -> "#{count / 60} minutes left!"
      _ -> nil
    end
  end

  @doc """
  Start a countdown.

  Inputs:
    * interval = duration of countdown in minutes
    * announce_every = interval (in minutes) to announce remaining time
    * speak = do you want the announcement to be audible? (only works on Mac)
  """
  def start(interval \\ 15, announce_every \\ 5, speak \\ false)
  def start(interval, announce_every, speak) do
    IO.puts("Pomodoro timer set for #{interval} minute(s) has begun...")

    timer = Stream.resource(
      fn -> interval * 60 end,
      fn
        0 -> {:halt, 0}
        time_remaining ->
          sleep(1)
          {[announce_time(time_remaining, announce_every * 60)], time_remaining - 1}
      end,
      fn _ -> nil end
    )
    |> Stream.each(&IO.puts/1)

    case speak do
      true -> timer |> Stream.each(&Pomodoro.say/1) |> Enum.to_list
      false -> timer |> Enum.to_list
    end
  end

end