From c9160efd8169760283d8bb5aa7f16162bc85833f Mon Sep 17 00:00:00 2001
From: r-vdp <ramses@well-founded.dev>
Date: Fri, 18 Oct 2024 11:18:39 +0200
Subject: [PATCH] nixos/kmonad: init

---
 nixos/modules/module-list.nix              |   1 +
 nixos/modules/services/hardware/kmonad.nix | 190 +++++++++++++++++++++
 2 files changed, 191 insertions(+)
 create mode 100644 nixos/modules/services/hardware/kmonad.nix

diff --git a/nixos/modules/module-list.nix b/nixos/modules/module-list.nix
index 6ac03cca94e9..c66b916d7d74 100644
--- a/nixos/modules/module-list.nix
+++ b/nixos/modules/module-list.nix
@@ -593,6 +593,7 @@
   ./services/hardware/irqbalance.nix
   ./services/hardware/joycond.nix
   ./services/hardware/kanata.nix
+  ./services/hardware/kmonad.nix
   ./services/hardware/lcd.nix
   ./services/hardware/libinput.nix
   ./services/hardware/lirc.nix
diff --git a/nixos/modules/services/hardware/kmonad.nix b/nixos/modules/services/hardware/kmonad.nix
new file mode 100644
index 000000000000..bc1b5409f9dd
--- /dev/null
+++ b/nixos/modules/services/hardware/kmonad.nix
@@ -0,0 +1,190 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+
+let
+  cfg = config.services.kmonad;
+
+  # Per-keyboard options:
+  keyboard =
+    { name, ... }:
+    {
+      options = {
+        name = lib.mkOption {
+          type = lib.types.str;
+          example = "laptop-internal";
+          description = "Keyboard name.";
+        };
+
+        device = lib.mkOption {
+          type = lib.types.path;
+          example = "/dev/input/by-id/some-dev";
+          description = "Path to the keyboard's device file.";
+        };
+
+        extraGroups = lib.mkOption {
+          type = lib.types.listOf lib.types.str;
+          default = [ ];
+          description = ''
+            Extra permission groups to attach to the KMonad instance for
+            this keyboard.
+
+            Since KMonad runs as an unprivileged user, it may sometimes
+            need extra permissions in order to read the keyboard device
+            file.  If your keyboard's device file isn't in the input
+            group you'll need to list its group in this option.
+          '';
+        };
+
+        defcfg = {
+          enable = lib.mkEnableOption ''
+            Automatically generate the defcfg block.
+
+            When this is option is set to true the config option for
+            this keyboard should not include a defcfg block.
+          '';
+
+          compose = {
+            key = lib.mkOption {
+              type = lib.types.nullOr lib.types.str;
+              default = "ralt";
+              description = "The (optional) compose key to use.";
+            };
+
+            delay = lib.mkOption {
+              type = lib.types.int;
+              default = 5;
+              description = "The delay (in milliseconds) between compose key sequences.";
+            };
+          };
+
+          fallthrough = lib.mkEnableOption "Re-emit unhandled key events.";
+
+          allowCommands = lib.mkEnableOption "Allow keys to run shell commands.";
+        };
+
+        config = lib.mkOption {
+          type = lib.types.lines;
+          description = "Keyboard configuration.";
+        };
+      };
+
+      config = {
+        name = lib.mkDefault name;
+      };
+    };
+
+  # Create a complete KMonad configuration file:
+  mkCfg =
+    keyboard:
+    let
+      defcfg = ''
+        (defcfg
+          input  (device-file "${keyboard.device}")
+          output (uinput-sink "kmonad-${keyboard.name}")
+          ${
+            lib.optionalString (keyboard.defcfg.compose.key != null) ''
+              cmp-seq ${keyboard.defcfg.compose.key}
+              cmp-seq-delay ${toString keyboard.defcfg.compose.delay}
+            ''
+          }
+          fallthrough ${lib.boolToString keyboard.defcfg.fallthrough}
+          allow-cmd ${lib.boolToString keyboard.defcfg.allowCommands}
+        )
+      '';
+    in
+    pkgs.writeTextFile {
+      name = "kmonad-${keyboard.name}.cfg";
+      text = lib.optionalString keyboard.defcfg.enable (defcfg + "\n") + keyboard.config;
+      checkPhase = "${cfg.package}/bin/kmonad -d $out";
+    };
+
+  # Build a systemd path config that starts the service below when a
+  # keyboard device appears:
+  mkPath =
+    keyboard:
+    let
+      name = "kmonad-${keyboard.name}";
+    in
+    lib.nameValuePair name {
+      description = "KMonad trigger for ${keyboard.device}";
+      wantedBy = [ "paths.target" ];
+      pathConfig = {
+        Unit = "${name}.service";
+        PathExists = keyboard.device;
+      };
+    };
+
+  # Build a systemd service that starts KMonad:
+  mkService =
+    keyboard:
+    let
+      cmd = [
+        (lib.getExe cfg.package)
+        "--input"
+        ''device-file "${keyboard.device}"''
+      ] ++ cfg.extraArgs ++ [ "${mkCfg keyboard}" ];
+    in
+    lib.nameValuePair "kmonad-${keyboard.name}" {
+      description = "KMonad for ${keyboard.device}";
+      script = lib.escapeShellArgs cmd;
+      unitConfig = {
+        # Control rate limiting.
+        # Stop the restart logic if we restart more than
+        # StartLimitBurst times in a period of StartLimitIntervalSec.
+        StartLimitIntervalSec = 2;
+        StartLimitBurst = 5;
+      };
+      serviceConfig = {
+        Restart = "always";
+        # Restart at increasing intervals from 2s to 1m
+        RestartSec = 2;
+        RestartSteps = 30;
+        RestartMaxDelaySec = "1min";
+        Nice = -20;
+        DynamicUser = true;
+        User = "kmonad";
+        Group = "kmonad";
+        SupplementaryGroups = [
+          # These ensure that our dynamic user has access to the device node
+          config.users.groups.input.name
+          config.users.groups.uinput.name
+        ] ++ keyboard.extraGroups;
+      };
+    };
+in
+{
+  options.services.kmonad = {
+    enable = lib.mkEnableOption "KMonad: An advanced keyboard manager.";
+
+    package = lib.mkPackageOption pkgs "kmonad" { };
+
+    keyboards = lib.mkOption {
+      type = lib.types.attrsOf (lib.types.submodule keyboard);
+      default = { };
+      description = "Keyboard configuration.";
+    };
+
+    extraArgs = lib.mkOption {
+      type = lib.types.listOf lib.types.str;
+      default = [ ];
+      example = [
+        "--log-level"
+        "debug"
+      ];
+      description = "Extra arguments to pass to KMonad.";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    hardware.uinput.enable = true;
+
+    systemd = {
+      paths = lib.mapAttrs' (_: mkPath) cfg.keyboards;
+      services = lib.mapAttrs' (_: mkService) cfg.keyboards;
+    };
+  };
+}