added enables to modules and made base module that imports all other modules

modules/default.nix

@@ -0,0 +1,8 @@
+{...}: {
+  imports = [
+    ./hardware.nix
+    ./users.nix
+    ./desktop.nix
+    ./nix-development.nix
+  ];
+}

modules/desktop.nix

@@ -1,41 +1,55 @@
-{pkgs, ...}: {
-  services = {
-    # Enable CUPS to print documents.
-    printing.enable = true;
+{
+  lib,
+  pkgs,
+  config,
+  ...
+}: {
+  options.host.desktop.enable = lib.mkEnableOption "should desktop configuration be enabled";
 
-    xserver = {
-      # Enable the X11 windowing system.
-      enable = true;
+  config = lib.mkMerge [
+    {
+      host.desktop.enable = lib.mkDefault true;
+    }
+    (lib.mkIf config.host.desktop.enable {
+      services = {
+        # Enable CUPS to print documents.
+        printing.enable = true;
 
-      # Enable the GNOME Desktop Environment.
-      displayManager.gdm.enable = true;
-      desktopManager = {
-        gnome.enable = true;
+        xserver = {
+          # Enable the X11 windowing system.
+          enable = true;
+
+          # Enable the GNOME Desktop Environment.
+          displayManager.gdm.enable = true;
+          desktopManager = {
+            gnome.enable = true;
+          };
+
+          # Get rid of xTerm
+          desktopManager.xterm.enable = false;
+          excludePackages = [pkgs.xterm];
+        };
+
+        pipewire = {
+          enable = true;
+          alsa.enable = true;
+          alsa.support32Bit = true;
+          pulse.enable = true;
+
+          # If you want to use JACK applications, uncomment this
+          #jack.enable = true;
+
+          # use the example session manager (no others are packaged yet so this is enabled by default,
+          # no need to redefine it in your config for now)
+          #media-session.enable = true;
+        };
       };
 
-      # Get rid of xTerm
-      desktopManager.xterm.enable = false;
-      excludePackages = [pkgs.xterm];
-    };
+      # Enable sound with pipewire.
+      hardware.pulseaudio.enable = false;
 
-    pipewire = {
-      enable = true;
-      alsa.enable = true;
-      alsa.support32Bit = true;
-      pulse.enable = true;
-
-      # If you want to use JACK applications, uncomment this
-      #jack.enable = true;
-
-      # use the example session manager (no others are packaged yet so this is enabled by default,
-      # no need to redefine it in your config for now)
-      #media-session.enable = true;
-    };
-  };
-
-  # Enable sound with pipewire.
-  hardware.pulseaudio.enable = false;
-
-  # enable RealtimeKit for pulse audio
-  security.rtkit.enable = true;
+      # enable RealtimeKit for pulse audio
+      security.rtkit.enable = true;
+    })
+  ];
 }

modules/nix-development.nix

@@ -1,14 +1,25 @@
 {
-  inputs,
+  lib,
+  config,
   pkgs,
+  inputs,
   ...
 }: {
-  nix = {
-    nixPath = ["nixpkgs=${inputs.nixpkgs}"];
-  };
+  options.host.nix-development.enable = lib.mkEnableOption "should desktop configuration be enabled";
 
-  environment.systemPackages = with pkgs; [
-    # nix langauge server
-    nixd
+  config = lib.mkMerge [
+    {
+      host.nix-development.enable = lib.mkDefault true;
+    }
+    (lib.mkIf config.host.nix-development.enable {
+      nix = {
+        nixPath = ["nixpkgs=${inputs.nixpkgs}"];
+      };
+
+      environment.systemPackages = with pkgs; [
+        # nix langauge server
+        nixd
+      ];
+    })
   ];
 }