{
  config,
  lib,
  allHosts,
  ...
}:
let
  cfg = config.custom.networking.overlay;
in
{
  options.custom.networking.overlay = {
    networkCidr = lib.mkOption {
      type = lib.types.nonEmptyStr;
      default = "10.254.250.0/24";
    };
    networkAddress = lib.mkOption {
      type = lib.types.nonEmptyStr;
      default = cfg.networkCidr |> lib.splitString "/" |> lib.head;
      readOnly = true;
    };
    prefixLength = lib.mkOption {
      type = lib.types.ints.between 0 32;
      default = cfg.networkCidr |> lib.splitString "/" |> lib.last |> lib.toInt;
      readOnly = true;
    };
    domain = lib.mkOption {
      type = lib.types.nonEmptyStr;
      default = "splitleaf.de";
    };
    fqdn = lib.mkOption {
      type = lib.types.nonEmptyStr;
      default = "${config.custom.networking.hostName}.${cfg.domain}";
    };

    address = lib.mkOption {
      type = lib.types.nonEmptyStr;
      default = "";
    };
    cidr = lib.mkOption {
      type = lib.types.nonEmptyStr;
      default = "${cfg.address}/${toString cfg.prefixLength}";
      readOnly = true;
    };
    interface = lib.mkOption {
      type = lib.types.nonEmptyStr;
      default = "nebula";
    };
    systemdUnit = lib.mkOption {
      type = lib.types.nonEmptyStr;
      default = "nebula@mesh.service";
    };

    isLighthouse = lib.mkEnableOption "";

    advertise = {
      address = lib.mkOption {
        type = lib.types.nullOr lib.types.nonEmptyStr;
        default =
          if config.custom.networking.underlay.isPublic then
            config.custom.networking.underlay.address
          else
            null;
      };
      port = lib.mkOption {
        type = lib.types.nullOr lib.types.port;
        default = if cfg.advertise.address != null then config.custom.services.nebula.listenPort else null;
      };
    };

    role = lib.mkOption {
      type = lib.types.enum [
        "client"
        "server"
      ];
    };

    dnsServers = lib.mkOption {
      type = lib.types.anything;
      default =
        allHosts
        |> lib.attrValues
        |> lib.filter (host: host.config.custom.services.recursive-nameserver.enable)
        |> lib.map (
          host:
          "${host.config.custom.networking.overlay.address}:${toString host.config.custom.services.recursive-nameserver.port}"
        );
    };

    implementation = lib.mkOption {
      type = lib.types.enum [ "nebula" ];
      default = "nebula";
    };
  };
}