nixos-config/nixos/components/gui/kmonad.nix

{ config, pkgs, lib, ... }:
{

  options.components.gui.kmonad.enable = lib.mkOption {
    type = lib.types.bool;
    default = config.components.gui.enable;
  };

  config = lib.mkIf (config.components.gui.kmonad.enable) {

    # only needed if you have an UHK
    hardware.keyboard.uhk.enable = true;
    environment.systemPackages = [ pkgs.unstable.uhk-agent ];
    users.users.mainUser.extraGroups = [ "input" ];

    services.xserver = {
      layout = "us";
      xkbOptions = "compose:ralt";
    };

    services.kmonad = {
      enable = true;
      keyboards =
        let
          keyboard = device: leftOfSpace: {
            device = device;
            extraGroups = [ "video" ];
            defcfg = {
              enable = true;
              fallthrough = true;
              allowCommands = true;
            };
            config = ''
              (defsrc
                grv  1    2    3    4    5    6    7    8    9    0    -    =    bspc
                tab  q    w    e    r    t    y    u    i    o    p    [    ]    \
                caps a    s    d    f    g    h    j    k    l    ;    '    ret
                lsft z    x    c    v    b    n    m    ,    .    /    rsft
                ${lib.concatStringsSep " " leftOfSpace}           spc            ralt rmet cmp  rctl
              )

              (defalias sym (layer-toggle symbols))
              (defalias alt (around (layer-toggle alt-qwerty)
                                    (layer-toggle arrows)))

              (deflayer qwerty
                grv  1    2    3    4    5    6    7    8    9    0    -    =    bspc
                tab  q    w    e    r    t    y    u    i    o    p    [    ]    \
                esc  a    s    d    f    g    h    j    k    l    ;    '    ret
                lsft z    x    c    v    b    n    m    ,    .    /    rsft
                lctl lmet @alt           spc            @sym rmet cmp  rctrl
              )

              (deflayer symbols
                _    ½    ²    ³    ⁴    ⁵    ⁶    ⁷    ⁸    ⁹    ∞    _    _    _
                _    _    _    €    _    ™    _    ü    _    ö    _    _    _    _
                caps ä    ß    _    _    _    _    _    _    _    _    _    _
                _    _    _    ¢    _    _    _    _    _    _    _    _
                _    _    _              _              _    _    _    _)

              (deflayer alt-qwerty
                (around lalt grv ) (around lalt 1) (around lalt 2) (around lalt 3) (around lalt 4) (around lalt 5  ) (around lalt 6) (around lalt 7) (around lalt 8) (around lalt 9) (around lalt 0) (around lalt -   ) (around lalt =  ) (around lalt bspc)
                _                  (around lalt q) (around lalt w) (around lalt e) (around lalt r) (around lalt t  ) (around lalt y) (around lalt u) (around lalt i) (around lalt o) (around lalt p) (around lalt [   ) (around lalt ]  ) (around lalt \   )
                _                  (around lalt a) (around lalt s) (around lalt d) (around lalt f) (around lalt g  ) (around lalt h) (around lalt j) (around lalt k) (around lalt l) (around lalt ;) (around lalt '   ) (around lalt ret)
                _                  (around lalt z) (around lalt x) (around lalt c) (around lalt v) (around lalt b  ) (around lalt n) (around lalt m) (around lalt ,) (around lalt .) (around lalt /) (around lalt rsft)
                _                  _                  _                                            (around lalt spc)                                 _               _               _               _
              )

              (deflayer arrows
                _    _    _    _    _    _    _    _    _    _     _    _    _    _
                _    _    _    _    _    _    _    _    up   _     _    _    _    _
                lalt _    _    _    _    _    _    left down right _    _    _
                _    _    _    _    _    _    _    _    _    _     _    _
                _    _    _              _              _    _     _    _)
            '';
          };

          # alt                => alt
          # alt + shift        => alt + shift
          # alt + jkli         => left down right up
          # alt + shift + jkli => alt + left down right up

        in
        {
          nativ = keyboard "/dev/input/by-path/platform-i8042-serio-0-event-kbd" [ "lctl" "lmet" "lalt" ];
          dasKeyboard = keyboard "/dev/input/by-id/usb-Metadot_-_Das_Keyboard_Das_Keyboard-event-kbd" [ "lctl" "lmet" "lalt" ];
          uhk = keyboard "/dev/input/by-id/usb-Ultimate_Gadget_Laboratories_UHK_60_v2-if01-event-kbd" [ "lctl" "lmet" "lalt" ];
        };
    };
  };
}