Nomarchy/modules/home/dock-audio.nix

# Automatic audio-output follow for docks / external monitors (#100).
# WirePlumber's stored default outranks priority.session, and some HDMI
# codecs only expose their usable route after the display hotplug.  The
# Hyprland monitor watcher therefore calls `reprobe monitoradded` for the
# unambiguous physical-plug event: restart the graph (the recovery used by
# the old working flake), wait for it to settle, then explicitly select an
# available dock-class sink.  Ordinary sink changes never select anything,
# so a manual speaker choice sticks until a fresh monitor plug.
{ config, lib, pkgs, ... }:

let
  cfg   = config.nomarchy;
  rules = import ../nixos/dock-audio-rules.nix;
  dockSinkRe = lib.concatStringsSep "|"
    (map (m: lib.removePrefix "~" m."node.name")
      (lib.concatMap (r: r.matches) rules."monitor.alsa.rules"));

  tool = pkgs.writeShellScriptBin "nomarchy-dock-audio" ''
    set -u
    PACTL=${pkgs.pulseaudio}/bin/pactl
    JQ=${pkgs.jq}/bin/jq
    SYSTEMCTL=${pkgs.systemd}/bin/systemctl
    LOGGER=${pkgs.util-linux}/bin/logger
    rt="''${XDG_RUNTIME_DIR:-/run/user/$(id -u)}"
    lock="$rt/nomarchy-dock-audio-reprobe.lock"
    TAB=$(printf '\t')

    log() { "$LOGGER" -t nomarchy-dock-audio -- "$*"; }
    wait_for_pulse() {
      tries=0
      while [ "$tries" -lt 40 ]; do
        "$PACTL" info >/dev/null 2>&1 && return 0
        tries=$((tries+1)); sleep 0.25
      done
      return 1
    }

    # Highest-priority dock-class sink whose active port is not explicitly
    # unavailable.  With pro-audio profiles a sink may have no ports; its
    # existence is then the only availability signal PipeWire exposes.
    dock_sinks() {
      "$PACTL" --format=json list sinks 2>/dev/null \
        | "$JQ" -r --arg re '^(${dockSinkRe})$' '
            [ .[] as $sink
              | $sink
              | select(.name | test($re))
              | select(
                  ((.ports // []) | length) == 0
                  or .active_port == null
                  or ([.ports[]?
                        | select(.name == $sink.active_port)
                        | (.availability // "unknown")][0]
                      // "unknown") != "not available"
                ) ]
            | sort_by(.priority // 0) | reverse[]
            | "\(.name)\t\(.description // .name)"'
    }

    select_first_dock() { # $1 = observable trigger
      trigger="$1"
      candidate=$(dock_sinks | ${pkgs.coreutils}/bin/head -n 1) || candidate=
      if [ -z "$candidate" ]; then
        log "trigger=$trigger result=no-available-dock-sink"
        return 1
      fi
      name=''${candidate%%"$TAB"*}
      desc=''${candidate#*"$TAB"}
      if "$PACTL" set-default-sink "$name" 2>/dev/null; then
        log "trigger=$trigger selected=$name description=$desc"
        ${pkgs.libnotify}/bin/notify-send -a Nomarchy "Audio" \
          "Output → $desc" 2>/dev/null || true
        return 0
      fi
      log "trigger=$trigger result=set-default-failed candidate=$name"
      return 1
    }

    case "''${1:-watch}" in
      candidates)
        dock_sinks ;;
      select)
        wait_for_pulse || { log "trigger=''${2:-manual} result=pulse-unavailable"; exit 1; }
        select_first_dock "''${2:-manual}" ;;
      reprobe)
        trigger="''${2:-monitoradded}"
        # mkdir is the debounce/lock: simultaneous monitoradded events from
        # an MST dock collapse into one graph restart.  Runtime-only state,
        # removed on every exit path.
        if ! ${pkgs.coreutils}/bin/mkdir "$lock" 2>/dev/null; then
          log "trigger=$trigger result=debounced"
          exit 0
        fi
        trap '${pkgs.coreutils}/bin/rmdir "$lock" 2>/dev/null || true' EXIT INT TERM
        log "trigger=$trigger action=reprobe-start"
        sleep 2
        "$SYSTEMCTL" --user restart \
          pipewire.service pipewire-pulse.service wireplumber.service \
          >/dev/null 2>&1 || log "trigger=$trigger action=graph-restart-returned-error"
        if wait_for_pulse; then
          sleep 0.75
          select_first_dock "$trigger" || true
        else
          log "trigger=$trigger result=pulse-did-not-return"
        fi ;;
      watch)
        # Selection is deliberately NOT done at service startup: a restart or
        # relogin while docked must not erase a manual speaker choice.  Only
        # the compositor's fresh monitoradded event calls `reprobe`.
        wait_for_pulse || true
        # A graph restart closes `pactl subscribe`, sometimes with status 0.
        # Always resubscribe; log one concise closure line for diagnosis.
        while :; do
          if LC_ALL=C "$PACTL" subscribe 2>/dev/null \
              | while IFS= read -r line; do
                  case "$line" in
                    *"'new' on sink"*|*"'change' on card"*) : ;;
                  esac
                done
          then status=0; else status=$?; fi
          log "subscription-closed status=$status; retrying"
          sleep 1
          wait_for_pulse || sleep 1
        done ;;
      *)
        echo "usage: nomarchy-dock-audio [watch|candidates|select [trigger]|reprobe [trigger]]" >&2
        exit 64 ;;
    esac
  '';
in
{
  config = lib.mkIf cfg.dockAudio.enable {
    home.packages = [ tool ];
    systemd.user.services.nomarchy-dock-audio = {
      Unit = {
        Description = "Reprobe and select dock/monitor audio on display hotplug";
        After  = [ "graphical-session.target" ];
        PartOf = [ "graphical-session.target" ];
      };
      Service = {
        ExecStart  = "${tool}/bin/nomarchy-dock-audio watch";
        Restart    = "on-failure";
        RestartSec = 2;
      };
      Install.WantedBy = [ "graphical-session.target" ];
    };
  };
}