{ lib, ... }:
  let
    inherit (lib)
      mkOption
      mkEnableOption
      mkIf
      types
    ;

    winType = types.submodule (
      { config, ... }: {
        options = {
          dualboot = {
            enable = mkEnableOption "dual boot";

            linuxPercentage = mkOption {
              type = types.number;
              description = "The percentage of the disk size reserved for Linux.";
            };
          };
        };

        config = {
          dualboot.linuxPercentage = mkIf (!config.dualboot.enable) 0;
        };
      });
  in {
    options = {
      valhalla = {
        windows = mkOption {
          type = winType;
          description = "The options for setting up Windows.";
          default = {};
        };
      };
    };
  }