refactor works on lio host

common/desktop_environment/default.nix

@@ -0,0 +1,30 @@
+{ config, lib, ... }:
+let
+  ccfg = import ../config.nix;
+  cfg = config.${ccfg.custom_config_key}.desktopEnvironment;
+in
+{
+  imports = [
+    ./gnome
+  ];
+  config = {
+    assertions = [
+      (
+        let
+          enabledDEs = lib.filter (x: x.enabled) [
+            {
+              name = "gnome";
+              enabled = cfg.gnome.enable;
+            }
+          ];
+        in
+        {
+          assertion = lib.length enabledDEs <= 1;
+          message =
+            "Only one desktop environment can be enabled at a time. Enabled: "
+            + lib.concatStringsSep ", " (map (x: x.name) enabledDEs);
+        }
+      )
+    ];
+  };
+}