{ lib, ... }:

let
  cfg = config.networking;
in

{
  options = {
    # from https://github.com/NixOS/nixpkgs/blob/799ba5bffed04ced7067a91798353d360788b30d/nixos/modules/tasks/network-interfaces.nix

    networking.hostName = mkOption {
      default = config.system.nixos.distroId;
      defaultText = literalExpression "config.system.nixos.distroId";
      type = types.strMatching
        "^$|^[[:alnum:]]([[:alnum:]_-]{0,61}[[:alnum:]])?$";
    };

    networking.fqdn = mkOption {
      readOnly = true;
      type = types.str;
      default = if (cfg.hostName != "" && cfg.domain != null)
        then "${cfg.hostName}.${cfg.domain}"
        else throw ''
          The FQDN is required but cannot be determined. Please make sure that
          both networking.hostName and networking.domain are set properly.
        '';
      defaultText = literalExpression ''"''${networking.hostName}.''${networking.domain}"'';
      description = ''
        The fully qualified domain name (FQDN) of this host. It is the result
        of combining `networking.hostName` and `networking.domain.` Using this
        option will result in an evaluation error if the hostname is empty or
        no domain is specified.

        Modules that accept a mere `networking.hostName` but prefer a fully qualified
        domain name may use `networking.fqdnOrHostName` instead.
      '';
    };

  };
}