{ config, lib, pkgs, ... }:

with lib;

let

  ladspaPath = "${pkgs.ladspaPlugins}/lib/ladspa";

  jackScript = pkgs.writeShellScriptBin "jack" (lib.fileContents <assets/jack.sh>);

  queueElement = {
    options = {
      plugin = mkOption {
        type        = with types; str;
        description = "file name without suffix of the plugin";
      };
      label = mkOption {
        type        = with types; str;
        description = "label of the queue element (needs to be correct)";
      };
      control = mkOption {
        type        = with types; listOf str;
        description = "parameter of plugin";
      };
    };
  };

  sinkElement = {
    options = {
      name = mkOption {
        type        = with types; str;
        description = "name of the sink";
      };
      queue = mkOption {
        type        = with types; listOf (submodule queueElement);
        description = "queues";
      };
    };
  };

  cfg = config.system.custom.audio;

in {

  options.system.custom.audio = {
    enable = mkEnableOption "use PluseAudio";
    sinks  = mkOption {
      type        = with types; listOf (submodule sinkElement);
      description = "list of sinks";
    };
  };

  config = mkIf cfg.enable {

    # add virtual midi module
    # -----------------------
    boot = {
      # to route midi signals
      # between bitwig and vcvrack
      kernelModules = [ "snd_virmidi" ];
      # index=-2  prevents from beeing recognised as the default
      #           audio device
      # midi_devs limit the number of midi devices.
      extraModprobeConfig = "options snd-virmidi index=-2 midi_devs=1";
    };

    # LADSPA
    # ------
    programs.bash.interactiveShellInit = /* sh */ ''
    # set ladspa library path
    # about testing the plugins check analyseplugin command
    export LADSPA_PATH=${ladspaPath}
    '';
    programs.zsh.interactiveShellInit = /* sh */ ''
    # set ladspa library path
    # about testing the plugins check analyseplugin command
    export LADSPA_PATH=${ladspaPath}
    '';

    # PulseAudio
    # ----------

    # because of systemWide ensure main user is in audio group
    system.custom.mainUser.extraGroups = [ "audio" ];

    hardware.pulseaudio = {
      enable  = true;

      # all in audio group can do audio
      systemWide = true;

      package = pkgs.pulseaudioFull;

      extraConfig = ''

      # automatically switch to newly-connected devices
      load-module module-switch-on-connect

      # http://plugin.org.uk/ladspa-swh/docs/ladspa-swh.html
      # https://gavv.github.io/articles/pulseaudio-under-the-hood/#ladspa-plugin-sink
      ${builtins.toString (flip map cfg.sinks (sink : ''
        # ladspa sink : ${sink.name}
        # -------------
        ${builtins.toString (flip imap0 (reverseList sink.queue) (index : queua:
        let
          sinkName        = suffix : "${sink.name}${builtins.toString suffix}";
          sinkValue       = "sink_name=${sinkName index}";
          sinkDescription = "sink_properties=device.description=${sinkName index}-${queua.label}";
          masterValue     = if (index == 0) then "" else "master=${sinkName (index - 1)}";
          pluginValue     = "plugin=${ladspaPath}/${queua.plugin}";
          labelValue      = "label=${queua.label}";
          controlValue    = "control=${builtins.toString (foldl (a: b: "${a},${b}") (head queua.control) (tail queua.control))}";
        in ''
          # ${sinkName index} : ${queua.label}
          load-module module-ladspa-sink ${sinkValue} ${sinkDescription} ${masterValue} ${pluginValue} ${labelValue} ${controlValue}
        ''))}
      ''))}
    '';
    };

    # Packages needed
    # ---------------
    environment.systemPackages = with pkgs ; [

      jackScript

      # Music making
      jack2Full
      alsaUtils
      patchage
      zynaddsubfx

      # qjackctl


      # LADSPA
      # ------
      ladspaPlugins
      ladspa-sdk

      # PulseAudio control
      # ------------------
      pavucontrol
      lxqt.pavucontrol-qt

    ];

  };

}