music.exs

defmodule Midi do
  use GenServer
  require Logger

  def init(args) do
    {:ok, args}
  end

  def start_link do
    # Logger.info "Available devices: #{inspect PortMidi.devices}"
    {:ok, device} = PortMidi.open(:output, "Renoise MIDI-In")
    tick_period = 50
    Process.send_after(:midi, {:tick}, tick_period)
    GenServer.start_link(__MODULE__, %{
      current_tick: -1,
      # We could write down :os.system_time(:milli_seconds) later
      # to dynamically recompute ticks based on elapsed time
      # and correct for drift
      device: device,
      tick_period: tick_period
    }, name: :midi)
  end

  def handle_info({:tick}, state) do
    # Immediately reschedule the next tick to reduce drift
    Process.send_after(:midi, {:tick}, state.tick_period)
    current_tick = Map.fetch!(state, :current_tick) + 1
    
    show_visual_feedback(current_tick)
    
    play_notes(state.device, current_tick)
    
    {:noreply, %{state | current_tick: current_tick}}
  end

  def handle_info({:note_off, note}, state) do
    PortMidi.write(state.device, {0x90, note, 0})
    {:noreply, state}
  end
  
  def show_visual_feedback(current_tick) do
    if rem(current_tick, 64) == 0 do
      IO.write IO.ANSI.clear <> IO.ANSI.home
    end
    if rem(current_tick, 8) == 0 do
      IO.write IO.ANSI.yellow <> to_string(1 + round(rem(current_tick, 64) / 8)) <> IO.ANSI.default_color
    end
  end
  
  def play_notes(device, current_tick) do
    notes = [0x54]
    delay = 16
    # notes = [0x54, 0x57, 0x5B, 0x60]
    # delay = 4
    volume = 00
    increase = 0
    
    notes = notes ++ Enum.reverse(notes)
    if rem(current_tick, delay) == 0 do
      index = rem(div(current_tick, delay), Enum.count(notes))
      note = Enum.at(notes, index) + increase
      PortMidi.write(device, {0x90, note, volume})
      Process.send_after(:midi, {:note_off, note}, 50 * 2)
    end
  end
end