#!/usr/bin/env python3
# Listen to the Logitech H390 inline volume/mute buttons (they arrive as HID
# keyboard events on the BOARD, since the headset is plugged into the board) and
# apply them to the headset PipeWire sink. Headless => no desktop consumes these,
# so without this daemon the inline buttons do nothing.
import glob, os, re, struct, subprocess, time

RUNTIME = "/run/user/1000"
USER = "callrec"
HSSINK = "alsa_output.usb-Logi_USB_Headset_Logi_USB_Headset-00.analog-stereo"
DEV_NAME_RE = re.compile(r"Logi USB Headset", re.I)

# linux input_event (64-bit): struct timeval(2*long) + u16 type + u16 code + s32 value
EV_FMT = "llHHi"
EV_SIZE = struct.calcsize(EV_FMT)
EV_KEY = 0x01
KEY_MUTE, KEY_VOLUMEDOWN, KEY_VOLUMEUP = 113, 114, 115

def pactl(*args):
    subprocess.run(["sudo", "-u", USER, "env", f"XDG_RUNTIME_DIR={RUNTIME}",
                    "pactl", *args], check=False,
                   stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)

def find_event_device():
    # match the event handler of the input device whose Name contains "Logi USB
    # Headset" and that reports key events (EV=... has bit 1). Parse
    # /proc/bus/input/devices so we survive event-number changes across reboots.
    try:
        blocks = open("/proc/bus/input/devices").read().split("\n\n")
    except OSError:
        return None
    for b in blocks:
        if not DEV_NAME_RE.search(b):
            continue
        m = re.search(r"Handlers=.*?(event\d+)", b)
        if m:
            return "/dev/input/" + m.group(1)
    return None

def run():
    dev = None
    while True:
        path = find_event_device()
        if not path or not os.path.exists(path):
            time.sleep(2); continue
        try:
            dev = open(path, "rb", buffering=0)
        except OSError:
            time.sleep(2); continue
        try:
            while True:
                data = dev.read(EV_SIZE)
                if not data or len(data) < EV_SIZE:
                    break
                _, _, etype, code, value = struct.unpack(EV_FMT, data)
                if etype != EV_KEY or value == 0:      # key release => ignore
                    continue
                if code == KEY_VOLUMEUP:
                    pactl("set-sink-volume", HSSINK, "+4%")
                elif code == KEY_VOLUMEDOWN:
                    pactl("set-sink-volume", HSSINK, "-4%")
                elif code == KEY_MUTE and value == 1:
                    pactl("set-sink-mute", HSSINK, "toggle")
        except OSError:
            pass
        finally:
            try: dev.close()
            except Exception: pass
        time.sleep(1)   # device vanished (unplug/reboot) -> re-find

if __name__ == "__main__":
    run()