meta: Make system module customizable

modules/system.nix

@@ -1,15 +1,36 @@
-{ pkgs, ... }:
+{ pkgs, lib, config, ... }:
 
 let
+  inherit (lib) mkOption;
+  inherit (lib.types) str listOf;
   inherit (pkgs.nixVersions) nix_2_19;
 
-  # TODO: Make these variables options
+  cfg = config.modules.system;
-  timeZone = "America/New_York";
-  defaultLocale = "ja_JP.UTF-8";
-  supportedLocales = [ "ja_JP.UTF-8/UTF-8" "en_US.UTF-8/UTF-8" "fr_FR.UTF-8/UTF-8" ];
-  stateVersion = "22.11";
 in
 {
+  options.modules.system = {
+    timeZone = mkOption {
+      type = str;
+      default = "America/New_York";
+    };
+
+    defaultLocale = mkOption {
+      type = str;
+      default = "ja_JP.UTF-8";
+    };
+
+    supportedLocales = mkOption {
+      type = listOf str;
+      default = [ "ja_JP.UTF-8/UTF-8" "en_US.UTF-8/UTF-8" "fr_FR.UTF-8/UTF-8" ];
+    };
+
+    stateVersion = mkOption {
+      type = str;
+      default = "22.11";
+    };
+  };
+
+  config = {
     boot = {
       tmp.cleanOnBoot = true;
 
@@ -46,14 +67,15 @@ in
     };
 
     time = {
-    inherit timeZone;
+      inherit (cfg) timeZone;
     };
 
     i18n = {
-    inherit defaultLocale supportedLocales;
+      inherit (cfg) defaultLocale supportedLocales;
     };
 
     system = {
-    inherit stateVersion;
+      inherit (cfg) stateVersion;
+    };
   };
 }