#!/usr/bin/env bash
# Record what an application plays, with no sound card present.
#
#   audio-capture start                 bring up a null sink named `cap`
#   audio-capture record OUT.wav &      record from it until killed
#   audio-capture run OUT.wav -- CMD…   start, run CMD, stop, leave OUT.wav
#
# A null sink is a real device as far as the application is concerned: the
# emulator and Godot open it exactly as they would hardware, and its monitor
# source is what `parec` reads. This is the difference between "the file decodes"
# and "the game played this" -- the second is a measurement, the first is not.
#
# Nothing here says the audio SOUNDS right; it says what was emitted. A human
# listening still answers something none of this does.
set -euo pipefail

SINK="${SYLPH_SINK:-cap}"

ensure_daemon() {
  pulseaudio --check 2>/dev/null || pulseaudio --start --exit-idle-time=-1 2>/dev/null || true
  for _ in $(seq 30); do pactl info >/dev/null 2>&1 && return 0; sleep 0.2; done
  echo "audio-capture: no PulseAudio daemon" >&2; return 1
}

case "${1:-}" in
  start)
    ensure_daemon
    pactl list short sinks | grep -q "^[0-9]*[[:space:]]*$SINK[[:space:]]" \
      || pactl load-module module-null-sink sink_name="$SINK" \
           sink_properties=device.description="$SINK" >/dev/null
    pactl set-default-sink "$SINK"
    echo "audio-capture: sink '$SINK' ready; point apps at it with PULSE_SINK=$SINK"
    ;;
  record)
    out="${2:?usage: audio-capture record OUT.wav}"
    ensure_daemon
    exec parec -d "${SINK}.monitor" --file-format=wav "$out"
    ;;
  run)
    out="${2:?usage: audio-capture run OUT.wav -- COMMAND...}"; shift 2
    [ "${1:-}" = "--" ] && shift
    "$0" start
    parec -d "${SINK}.monitor" --file-format=wav "$out" & rec=$!
    # Kill the recorder on any exit path, or a failed run leaves it holding the
    # monitor and the next capture silently records nothing.
    trap 'kill "$rec" 2>/dev/null || true' EXIT
    PULSE_SINK="$SINK" "$@" || true
    sleep 1; kill "$rec" 2>/dev/null || true; wait "$rec" 2>/dev/null || true
    trap - EXIT
    if [ -s "$out" ]; then
      dur=$(ffprobe -v error -show_entries format=duration -of csv=p=0 "$out" 2>/dev/null || echo "?")
      echo "audio-capture: $out (${dur}s)"
      # Silence is the failure that looks like success: a WAV of the right
      # length, full of zeroes, because the app opened a different sink.
      peak=$(ffmpeg -hide_banner -i "$out" -af astats=measure_perchannel=none -f null - 2>&1 \
               | grep -m1 "Peak level" || true)
      echo "            ${peak:-no level measured}"
      case "$peak" in *"-inf"*) echo "            WARNING: silent -- did the app use this sink?" ;; esac
    else
      echo "audio-capture: nothing recorded" >&2; exit 1
    fi
    ;;
  *) sed -n '2,12p' "$0" | sed 's/^# \{0,1\}//' ;;
esac