uno-q-audio-synth/scripts/midi-bridge.py

#!/usr/bin/env python3
"""Bridge raw MIDI device to Pd via UDP. Auto-detects gadget vs host mode.

Sends parsed MIDI messages as Pd-style 'midi status data1 data2;' strings
to UDP ports for Pd (8081) and LED matrix visualization (8082).

Writes metrics to /tmp/midi-stats.json for prometheus-exporter to collect.
"""
import os, socket, time, select, pathlib, json, threading

PD_HOST = os.environ.get("MIDI_BRIDGE_HOST", "127.0.0.1")
PD_PORT = int(os.environ.get("MIDI_BRIDGE_PORT", "8081"))
VIZ_PORT = int(os.environ.get("VIZ_PORT", "8082"))
STATS_FILE = os.environ.get("MIDI_STATS_FILE", "/tmp/midi-stats.json")
STATS_INTERVAL = 2.0

midi_notes_on = 0
midi_notes_off = 0
midi_messages_total = 0
midi_errors = 0
last_status = 0
last_note = 0
last_velocity = 0
last_time = 0.0
_stats_lock = threading.Lock()


def _find_midi_dev():
    """Auto-detect rawmidi device. Preference: gadget f_midi > env override > host mode."""
    dev = os.environ.get("MIDI_BRIDGE_DEV")
    if dev:
        return dev
    cards = pathlib.Path("/proc/asound").glob("card*")
    for card_dir in cards:
        cmi = card_dir / "id"
        if cmi.exists() and "midi" in cmi.read_text().strip():
            card_num = card_dir.name.replace("card", "")
            midi_dev = f"/dev/snd/midiC{card_num}D0"
            if os.path.exists(midi_dev):
                return midi_dev
    rawdevs = sorted(pathlib.Path("/dev/snd").glob("midiC?D0"))
    if rawdevs:
        return str(rawdevs[0])
    return "/dev/snd/midiC0D0"


def midi_msg(status, data1, data2=None):
    if data2 is not None:
        return f"midi {status} {data1} {data2};"
    return f"midi {status} {data1};"


def _open_midi():
    midi_dev = _find_midi_dev()
    while not os.path.exists(midi_dev):
        time.sleep(0.5)
        midi_dev = _find_midi_dev()
    fd = os.open(midi_dev, os.O_RDWR | os.O_NONBLOCK)
    os.set_blocking(fd, False)
    return fd


def _flush(sock, buf):
    global midi_notes_on, midi_notes_off, midi_messages_total, midi_errors
    global last_status, last_note, last_velocity, last_time

    status = buf[0]
    if (buf[0] & 0xF0) == 0xF0:
        return
    status = (status & 0xF0) | 0
    data1 = buf[1]
    data2 = buf[2] if len(buf) >= 3 else None
    msg = midi_msg(status, data1, data2)
    sock.sendto(msg.encode(), (PD_HOST, PD_PORT))
    sock.sendto(msg.encode(), (PD_HOST, VIZ_PORT))

    with _stats_lock:
        midi_messages_total += 1
        last_status = status
        last_note = data1
        last_velocity = data2 if data2 is not None else 0
        last_time = time.time()
        msg_type = status & 0xF0
        if msg_type == 0x90 and (data2 or 0) > 0:
            midi_notes_on += 1
        elif msg_type == 0x80 or (msg_type == 0x90 and (data2 or 0) == 0):
            midi_notes_off += 1


def _write_stats():
    try:
        with open(STATS_FILE, "w") as f:
            json.dump({
                "midi_messages_total": midi_messages_total,
                "midi_notes_on_total": midi_notes_on,
                "midi_notes_off_total": midi_notes_off,
                "midi_errors_total": midi_errors,
                "midi_last_status": last_status,
                "midi_last_note": last_note,
                "midi_last_velocity": last_velocity,
                "midi_last_time_unix": last_time,
            }, f)
    except OSError:
        pass


def main():
    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    running = True
    last_stats_write = time.monotonic()

    while running:
        try:
            fd = _open_midi()
            poll = select.poll()
            poll.register(fd, select.POLLIN)
            buf = bytearray()
            while running:
                now = time.monotonic()

                # Write stats periodically
                if now - last_stats_write >= STATS_INTERVAL:
                    with _stats_lock:
                        _write_stats()
                    last_stats_write = now

                try:
                    events = poll.poll(100)
                    for f, flags in events:
                        if flags & select.POLLIN:
                            data = os.read(fd, 1024)
                            if not data:
                                continue
                            for byte in data:
                                if byte & 0x80:
                                    if len(buf) > 0 and buf[0] >= 0x80:
                                        _flush(sock, buf)
                                    buf = bytearray([byte])
                                else:
                                    buf.append(byte)
                                    if len(buf) >= 3 and (buf[0] & 0xE0) in (0x80, 0x90, 0xA0, 0xB0, 0xE0):
                                        _flush(sock, buf)
                                        buf = bytearray()
                                    elif len(buf) >= 2 and (buf[0] & 0xE0) in (0xC0, 0xD0):
                                        _flush(sock, buf)
                                        buf = bytearray()
                    if not events:
                        time.sleep(0.01)
                except OSError as e:
                    if e.errno == 19:
                        os.close(fd)
                        time.sleep(1)
                        break
                    raise
                except BlockingIOError:
                    pass
        except KeyboardInterrupt:
            running = False

    sock.close()


if __name__ == "__main__":
    main()