{ lib, ... }:
  let
    inherit (lib)
      mkOption
      types
    ;
  in {
    options = {
      valhalla = mkOption {
        type = types.submodule (
          { extendModules, ... }:
            let
              osVariant = extendModules {
                modules = [
                  ({ config, ... }: {
                    options = {
                      config = mkOption {
                        type = types.attrs;
                        description = "The configuration of the Operating System.";
                        default = builtins.removeAttrs config ["_module" "config" "linux" "windows"];
                        visible = false;
                      };
                    };
                  })
                ];
              };

              linuxVariant = osVariant.extendModules {
                modules = [
                  ({ ... }: {
                    options = {
                      secureBoot = mkOption {
                        type = types.bool;
                        description = "A value indicating whether the system supports Secure Boot.";
                        default = false;
                      };
                    };
                  })
                ];
              };

              windowsVariant = osVariant.extendModules { };
            in {
              options = {
                linux = mkOption {
                  inherit (linuxVariant) type;
                  description = "The options for setting up Linux.";
                  default = {};
                  visible = "shallow";
                };

                windows = mkOption {
                  inherit (windowsVariant) type;
                  description = "The options for setting up Windows.";
                  default = {};
                  visible = "shallow";
                };
              };
            });

        description = "Configuration for PortValhalla.";
        default = {};
      };
    };
  }