modularize desktop components

modules/desktop/dm/default.nix

@@ -0,0 +1,39 @@
+{ config, lib, ... }:
+
+let
+  cfg = config.desktop.dm;
+in
+{
+  options.desktop.dm = with lib; {
+    name = mkOption {
+      type = types.nullOr (types.enum ["sddm" "gdm"]);
+      default = null;
+      description = "The display manager to use.";
+    };
+    autologin = mkOption {
+      type = types.nullOr types.str;
+      default = null;
+      description = "The autologin username or null for no autologin.";
+    };
+    wayland = mkOption {
+      type = types.bool;
+      default = false;
+      description = "Enable wayland";
+    };
+  };
+
+  imports = [
+    ./gdm.nix
+    ./sddm.nix
+  ];
+
+  config = {
+    services.xserver.enable = true;
+    services.xserver = {
+      layout = "de";
+      xkbVariant = "";
+    };
+    services.xserver.displayManager.autoLogin.enable = (cfg.autologin != null);
+    services.xserver.displayManager.autoLogin.user = cfg.autologin;
+  };
+}

modules/desktop/dm/gdm.nix

@@ -0,0 +1,12 @@
+{ lib, config, ... }:
+let
+  cfg = config.desktop.dm;
+in
+{
+  config = lib.mkIf (cfg.name == "gdm") {
+    services.xserver.displayManager.gdm = {
+      enable = true;
+      wayland = cfg.wayland;
+    };
+  };
+}

modules/desktop/dm/sddm.nix

@@ -0,0 +1,13 @@
+{ lib, config, ... }:
+
+let
+  cfg = config.desktop.dm;
+in
+{
+  config = lib.mkIf (cfg.name == "sddm") {
+    services.xserver.displayManager.sddm = {
+      enable = true;
+      wayland.enable = cfg.wayland;
+    };
+  };
+}