refactor: modularize greeter

hosts/callisto/configuration.nix

@@ -27,6 +27,7 @@
     theming = {
       enable = true;
     };
+    desktop.greeter.enable = true;
   };
 
   boot = {

modules/linux/greeter/default.nix

@@ -1,5 +1,31 @@
-{ pkgs, ... }:
 {
+  pkgs,
+  lib,
+  config,
+  ...
+}:
+let
+  cfg = config.liminalOS.desktop.greeter;
+in
+{
+  options.liminalOS.desktop.greeter = {
+    enable = lib.mkOption {
+      type = lib.types.bool;
+      default = config.liminalOS.desktop.enable;
+      description = ''
+        Whether to enable and set up tui-greet, the default greeter for liminalOS.
+      '';
+    };
+    command = lib.mkOption {
+      type = lib.types.str;
+      default = if config.liminalOS.desktop.enable then "Hyprland" else "";
+      description = ''
+        Command for the greeter to execute to launch the desktop. If the liminalOS Hyprland Desktop is enabled, defaults to `Hyprland`.
+      '';
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
     services.greetd = {
       enable = true;
       settings = {
@@ -22,4 +48,5 @@
       TTYVHangup = true;
       TTYVTDisallocate = true;
     };
+  };
 }