Improve displayManager options

hosts/vm/default.nix

@@ -13,6 +13,7 @@
   ];
 
   modules.hyprland.enable = true;
+  modules.displayManager.displayManager = "gdm";
 
   modules.zsh.enable = true;
   modules.shell.defaultShell = "zsh";

hosts/vm/variables.nix

@@ -1,5 +0,0 @@
-{
-  # Set Display Manager
-  # 'gdm', 'sddm'
-  displayManager = "sddm";
-}

modules/core/default.nix

@@ -1,20 +1,13 @@
 {
-  host,
   ...
-}: let
-  vars = import ../../hosts/${host}/variables.nix;
-in {
+}:
+{
   imports = [
+    ./gdm.nix
     ./hyprland.nix
     ./packages.nix
+    ./sddm.nix
     ./system.nix
     ./user.nix
-  ]
-  ++ (
-    if vars.displayManager == "gdm"
-    then [ ./gdm.nix ]
-    else if vars.displayManager == "sddm"
-    then [ ./sddm.nix ]
-    else []
-  );
+  ];
 }

modules/core/gdm.nix

@@ -1,9 +1,17 @@
 {
+  config,
+  lib,
   ...
 }:
+with lib;
+let
+  cfg = config.modules.displayManager;
+in
 {
-  services.xserver.displayManager.gdm = {
-    enable = true;
-    wayland.enable = true;
+  config = mkIf (cfg.displayManager == "gdm") {
+    services.xserver.displayManager.gdm = {
+      enable = true;
+      wayland = true;
+    };
   };
 }

modules/core/sddm.nix

@@ -1,12 +1,20 @@
 {
+  config,
+  lib,
   ...
 }:
+with lib;
+let
+  cfg = config.modules.displayManager;
+in
 {
-  services.displayManager.sddm = {
-    enable = true;
-    wayland.enable = true;
-  };
+  config = mkIf (cfg.displayManager == "sddm") {
+    services.displayManager.sddm = {
+      enable = true;
+      wayland.enable = true;
+    };
 
-  # To prevent getting stuck at shutdown
-  systemd.extraConfig = "DefaultTimeoutStopSec=10s";
+    # To prevent getting stuck at shutdown
+    systemd.extraConfig = "DefaultTimeoutStopSec=10s";
+  };
 }

modules/options/default.nix

@@ -3,6 +3,7 @@
 }:
 {
   imports = [
+    ./displayManager.nix
     ./hyprland.nix
     ./shell.nix
     ./zsh.nix

modules/options/displayManager.nix

@@ -0,0 +1,23 @@
+{
+  config,
+  lib,
+  ...
+}:
+with lib;
+let
+  cfg = config.modules.displayManager;
+in
+{
+  options.modules.displayManager = {
+    displayManager = mkOption {
+      type = types.enum [
+        "gdm"
+        "sddm"
+      ];
+      default = "sddm";
+      description = ''
+        The display manager to use.
+      '';
+    };
+  };
+}