feat: add --watch option for support hot-plugging keyboards

[tangxinfa]

Use inotify to watch new keyboard devices

[Lenbok]

I'm excited for this, thanks!

I gave this a test but it didn't quite work. Here's what I get when I start it up, then unplug and re-plug my keyboard: (I'm using Ubuntu 18.04, if that helps)

$ sudo xkeysnail --watch ~/.xkeysnail.py

██╗  ██╗██╗  ██╗███████╗██╗   ██╗
╚██╗██╔╝██║ ██╔╝██╔════╝╚██╗ ██╔╝
 ╚███╔╝ █████╔╝ █████╗   ╚████╔╝
 ██╔██╗ ██╔═██╗ ██╔══╝    ╚██╔╝
██╔╝ ██╗██║  ██╗███████╗   ██║
╚═╝  ╚═╝╚═╝  ╚═╝╚══════╝   ╚═╝
  ███████╗███╗   ██╗ █████╗ ██╗██╗
  ██╔════╝████╗  ██║██╔══██╗██║██║
  ███████╗██╔██╗ ██║███████║██║██║
  ╚════██║██║╚██╗██║██╔══██║██║██║
  ███████║██║ ╚████║██║  ██║██║███████╗
  ╚══════╝╚═╝  ╚═══╝╚═╝  ╚═╝╚═╝╚══════╝
                             v0.1.0

No keyboard devices specified via (--devices) option.
xkeysnail picks up keyboard-ish devices from the list below:

---------------------------------------------------------------------------------------------
Device               Name                                Phys
---------------------------------------------------------------------------------------------
/dev/input/event0    Power Button                        PNP0C0C/button/input0
/dev/input/event1    Power Button                        LNXPWRBN/button/input0
/dev/input/event2    Microsoft Microsoft® 2.4GHz Transceiver v9.0 usb-0000:00:1d.0-1.7/input0
/dev/input/event3    Microsoft Microsoft® 2.4GHz Transceiver v9.0 usb-0000:00:1d.0-1.7/input1
/dev/input/event4    Microsoft Microsoft® 2.4GHz Transceiver v9.0 usb-0000:00:1d.0-1.7/input2
/dev/input/event5    Eee PC WMI hotkeys                  eeepc-wmi/input0
/dev/input/event6    HDA Intel PCH Front Mic             ALSA
/dev/input/event7    HDA Intel PCH Rear Mic              ALSA
/dev/input/event8    HDA Intel PCH Line                  ALSA
/dev/input/event9    HDA Intel PCH Line Out Front        ALSA
/dev/input/event10   HDA Intel PCH Line Out Surround     ALSA
/dev/input/event11   HDA Intel PCH Line Out CLFE         ALSA
/dev/input/event12   HDA Intel PCH Line Out Side         ALSA
/dev/input/event13   HDA Intel PCH Front Headphone       ALSA
/dev/input/event14   HDA NVidia HDMI/DP,pcm=3            ALSA
/dev/input/event15   HDA NVidia HDMI/DP,pcm=7            ALSA
/dev/input/event16   HDA NVidia HDMI/DP,pcm=8            ALSA
/dev/input/event17   HDA NVidia HDMI/DP,pcm=9            ALSA
/dev/input/event19   Falbatech The Redox Keyboard        usb-0000:00:1d.0-1.6.1.1/input0
/dev/input/event20   Falbatech The Redox Keyboard        usb-0000:00:1d.0-1.6.1.1/input1
/dev/input/event21   Falbatech The Redox Keyboard        usb-0000:00:1d.0-1.6.1.1/input2
/dev/input/event18   py-evdev-uinput                     py-evdev-uinput

Okay, now enable remapping on the following device(s):

---------------------------------------------------------------------------------------------
Device               Name                                Phys
---------------------------------------------------------------------------------------------
/dev/input/event2    Microsoft Microsoft® 2.4GHz Transceiver v9.0 usb-0000:00:1d.0-1.7/input0
/dev/input/event4    Microsoft Microsoft® 2.4GHz Transceiver v9.0 usb-0000:00:1d.0-1.7/input2
/dev/input/event19   Falbatech The Redox Keyboard        usb-0000:00:1d.0-1.6.1.1/input0

Watching keyboard devices plug in
Device removed: Falbatech The Redox Keyboard
Okay, now enable remapping on the following new device(s):

----------------------------------------------------------------------------------------
Device               Name                                Phys
----------------------------------------------------------------------------------------
/dev/input/event19   Falbatech The Redox Keyboard        usb-0000:00:1d.0-1.6.1.1/input0

Okay, now enable remapping on the following new device(s):

Traceback (most recent call last):
  File "/usr/local/bin/xkeysnail", line 6, in <module>
    cli_main()
  File "/usr/local/lib/python3.6/dist-packages/xkeysnail/__init__.py", line 50, in cli_main
    loop(args.devices, args.watch)
  File "/usr/local/lib/python3.6/dist-packages/xkeysnail/input.py", line 125, in loop
    print_device_list(new_devices)
  File "/usr/local/lib/python3.6/dist-packages/xkeysnail/input.py", line 38, in print_device_list
    print('-' * len(max(device_lines, key=len)))
ValueError: max() arg is an empty sequence

[tangxinfa]

@Lenbok I fixed the problem, please try again, thanks

[Lenbok]

Great, it's now working perfectly in my testing!

[mooz]

Wow, this is great! Thanks!