From 954598068ac5ebaa65915e08e25842cc582b39bf Mon Sep 17 00:00:00 2001
From: Yan Lin <github@yanlincs.com>
Date: Sat, 1 Nov 2025 22:30:07 +0100
Subject: [PATCH] add a module for automatically disable internal keyboard

---
 hosts/nixos/thinkpad/system.nix |  9 ++++
 modules/disable-keyboard.nix    | 73 +++++++++++++++++++++++++++++++++
 2 files changed, 82 insertions(+)
 create mode 100644 modules/disable-keyboard.nix

diff --git a/hosts/nixos/thinkpad/system.nix b/hosts/nixos/thinkpad/system.nix
index 7fae1c4..3665b1e 100644
--- a/hosts/nixos/thinkpad/system.nix
+++ b/hosts/nixos/thinkpad/system.nix
@@ -7,6 +7,7 @@
     ../../../modules/desktop.nix
     ../../../modules/wireguard.nix
     ../../../modules/login-display.nix
+    ../../../modules/disable-keyboard.nix
   ];
 
   # Bootloader - standard UEFI setup
@@ -242,12 +243,20 @@
             capslock = "leftcontrol";
             # Map Right Control to Caps Lock
             rightcontrol = "capslock";
+            # Map Left Alt to Super (Windows key)
+            leftalt = "leftmeta";
           };
         };
       };
     };
   };
 
+  # Disable internal keyboard when HHKB-Hybrid_1 is connected
+  services.disable-keyboard = {
+    enable = true;
+    externalKeyboardName = "HHKB-Hybrid_1";
+  };
+
   # Apply XKB config to console (TTY) as well
   console.useXkbConfig = true;
 
diff --git a/modules/disable-keyboard.nix b/modules/disable-keyboard.nix
new file mode 100644
index 0000000..66c167c
--- /dev/null
+++ b/modules/disable-keyboard.nix
@@ -0,0 +1,73 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.services.disable-keyboard;
+in
+
+{
+  options.services.disable-keyboard = {
+    enable = mkEnableOption "automatically disable internal keyboard when specific external keyboard is connected";
+
+    externalKeyboardName = mkOption {
+      type = types.str;
+      default = "";
+      example = "HHKB-Hybrid_1";
+      description = ''
+        The name of the external keyboard that triggers disabling the internal keyboard.
+        This should match the ATTRS{name} value shown in udevadm info or Bluetooth device settings.
+        Use `libinput list-devices` or `udevadm monitor` to find the exact name.
+      '';
+    };
+
+    internalKeyboardName = mkOption {
+      type = types.str;
+      default = "AT Translated Set 2 keyboard";
+      description = ''
+        The name of the internal keyboard to disable.
+        Default is "AT Translated Set 2 keyboard" which is standard for most laptops.
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+    # Install evtest package for grabbing keyboard input
+    environment.systemPackages = [ pkgs.evtest ];
+
+    # Systemd service to grab (disable) the internal keyboard
+    systemd.services.disable-keyboard = {
+      description = "Disable internal keyboard (${cfg.internalKeyboardName}) using evtest";
+      serviceConfig = {
+        Type = "simple";
+        # Wait for device to be ready, then find and grab the internal keyboard
+        ExecStartPre = "${pkgs.coreutils}/bin/sleep 2";
+        ExecStart = pkgs.writeShellScript "disable-keyboard" ''
+          # Find the event device for the internal keyboard
+          INTERNAL_KB_EVENT=$(${pkgs.gnugrep}/bin/grep -l "${cfg.internalKeyboardName}" /sys/class/input/event*/device/name 2>/dev/null | ${pkgs.gnused}/bin/sed 's|/sys/class/input/\(.*\)/device/name|/dev/input/\1|' | head -n1)
+
+          if [ -z "$INTERNAL_KB_EVENT" ]; then
+            echo "Internal keyboard '${cfg.internalKeyboardName}' not found"
+            exit 1
+          fi
+
+          echo "Disabling internal keyboard: $INTERNAL_KB_EVENT"
+          # Use evtest --grab to exclusively grab the device (prevents events from reaching the system)
+          exec ${pkgs.evtest}/bin/evtest --grab "$INTERNAL_KB_EVENT" > /dev/null 2>&1
+        '';
+        Restart = "on-failure";
+        RestartSec = "5s";
+      };
+      wantedBy = [];  # Don't start automatically on boot, only via udev trigger
+    };
+
+    # udev rules to detect external keyboard connection/disconnection
+    services.udev.extraRules = ''
+      # When the specified external keyboard connects, start the disable service
+      ACTION=="add", SUBSYSTEM=="input", ENV{ID_INPUT_KEYBOARD}=="1", ATTRS{name}=="${cfg.externalKeyboardName}", TAG+="systemd", ENV{SYSTEMD_WANTS}="disable-keyboard.service"
+
+      # When the external keyboard disconnects, stop the service (re-enable internal keyboard)
+      ACTION=="remove", SUBSYSTEM=="input", ENV{ID_INPUT_KEYBOARD}=="1", ATTRS{name}=="${cfg.externalKeyboardName}", RUN+="${pkgs.systemd}/bin/systemctl stop disable-keyboard.service"
+    '';
+  };
+}