fix erratic volume wheel on mouse with python-evdev and its uinput module

mousewheel_fixer.py

import evdev
import evdev.ecodes as e

device_name =  "Areson SPEEDLINK SCELUS Consumer Control"

TURN_AROUND_TIME = 0.2

devices = [evdev.InputDevice(p) for p in evdev.list_devices()]
right_ones = [d for d in devices if d.name == device_name]

if not right_ones:
    raise Exception(f"Could not find a device matching {device_name}")

if len(right_ones) > 1:
    raise Exception(f"Found more than one device matching {device_name}: {right_ones}")

mydev = right_ones[0]

with mydev.grab_context():
    output_dev = evdev.uinput.UInput.from_device(mydev)

    last_timestamp_by_keycode = {}
    last_timestamp_by_keycode[e.KEY_VOLUMEUP] = 0
    last_timestamp_by_keycode[e.KEY_VOLUMEDOWN] = 0

    current_key_state_by_keycode = {}
    current_key_state_by_keycode[e.KEY_VOLUMEUP] = 0
    current_key_state_by_keycode[e.KEY_VOLUMEDOWN] = 0

    output_dev.write(e.EV_KEY, e.KEY_VOLUMEUP, 0)
    output_dev.write(e.EV_KEY, e.KEY_VOLUMEDOWN, 0)

    for orig_event in mydev.read_loop():
        event = evdev.util.categorize(orig_event)
        # forward everything we don't care about through
        if not isinstance(event, evdev.events.KeyEvent):
            output_dev.write_event(orig_event)
            continue

        if event.scancode not in [e.KEY_VOLUMEUP, e.KEY_VOLUMEDOWN]:
            output_dev.write_event(orig_event)
            continue

        if event.keystate == 0:
            # allow through a release event if we think the key
            # is currently not released
            if current_key_state_by_keycode[event.scancode] != 0:
                current_key_state_by_keycode[event.scancode] = 0
                output_dev.write_event(orig_event)
            continue

        if event.keystate == 2:
            print("did not expect a keystate of 2, ignoring this event!", event)
            continue

        # we have a down event of one of the two keys
        # if it's been half a second since the last event, let it through
        most_recent_event_timestamp = max(last_timestamp_by_keycode.values())
        elapsed = orig_event.timestamp() - most_recent_event_timestamp
        print("last event was ", elapsed, " seconds ago.")
        if elapsed > TURN_AROUND_TIME:
            last_timestamp_by_keycode[event.scancode] = orig_event.timestamp()
            current_key_state_by_keycode[event.scancode] = event.keystate
            output_dev.write_event(orig_event)
            print("letting through ", event)
            continue
        else:
            if last_timestamp_by_keycode[event.scancode] == most_recent_event_timestamp:
                last_timestamp_by_keycode[event.scancode] = orig_event.timestamp()
                current_key_state_by_keycode[event.scancode] = event.keystate
                output_dev.write_event(orig_event)
                print("letting through! ", event)
                continue
            else:
                print("apparently wrong direction! ", event)

        print("event made it through the filter and was not accepted: ", event)