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

    cfg = config.valhalla;
    capitalize = (import ../text.nix { inherit lib; }).capitalize;
  in {
    options = {
      valhalla = {
        users = mkOption {
          type = types.attrsOf (types.submodule (
            { ... }: {
              options = {
                displayName = mkOption {
                  type = types.nullOr types.str;
                  description = "The human-readable name of the user.";
                  default = null;
                };

                mailAddress = mkOption {
                  type = types.nullOr types.str;
                  description = "The mail address of the user.";
                  default = null;
                };

                groups = mkOption {
                  type = types.listOf types.str;
                  description = "The additional groups of the user.";
                  default = [];
                };
              };
            }));
          description = "The users to create on the machine.";
          default = {};
        };

        linux.users = mkOption {
          type = types.attrsOf (types.submodule {
            options = {
              defaultShell = mkOption {
                type = types.nullOr types.str;
                description = "The default shell of the user.";
                default = null;
              };
            };
          });
        };

        windows.users = mkOption {
          type = types.attrsOf (types.submodule {
            options = {
              microsoftAccount = mkOption {
                type = types.bool;
                description = "A value indicating whether this user is a Microsoft Account.";
                default = false;
              };
            };
          });
        };
      };
    };

    config = {
      valhalla.windows.users = lib.mkForce (lib.attrsets.concatMapAttrs (
        name: options: {
            ${capitalize name} = options // {
              groups = [];
            };
          }) cfg.users);
    };
  }