nixos:
{ ipAddress ? null
, enableVpn ? false
, vpnConnectTo ? ""
, vpnRsaPrivateKeyFile ? null
, vpnEd25519PrivateKeyFile ? null
, configuration # see: configuration.nix(5)
}:
assert enableVpn -> builtins.isString ipAddress;
assert enableVpn -> builtins.isString vpnRsaPrivateKeyFile;
assert enableVpn -> builtins.isString vpnEd25519PrivateKeyFile;
let
  vpnExtraConfig = if enableVpn then ''
    ConnectTo = ${vpnConnectTo}
    Ed25519PrivateKeyFile = "${vpnEd25519PrivateKeyFile}"
    PrivateKeyFile = "${vpnRsaPrivateKeyFile}"
  '' else "";
  defaults = {
    boot.cleanTmpDir = true;
    #networking.interfaces.simatime-vpn = [{ ipv4.address = ipAddress; }];
    nix.binaryCaches = [ "https://cache.nixos.org" ];
    nix.gc.automatic = true;
    nix.gc.dates = "Sunday 02:15";
    nix.maxJobs = 1; # "auto";
    nix.optimise.automatic = true;
    nix.optimise.dates = [ "Sunday 02:30" ];
    security.sudo.wheelNeedsPassword = false;
    services.clamav.daemon.enable = true; # security
    services.clamav.updater.enable = true; # security
    services.fail2ban.enable = true; # security
    services.openssh.enable = true;
    services.openssh.openFirewall = true;
    services.openssh.forwardX11 = true;
    services.openssh.passwordAuthentication = false;
    services.tinc.networks.simatime-vpn.extraConfig = vpnExtraConfig;
    services.tinc.networks.simatime-vpn.debugLevel = 3;
    services.tinc.networks.simatime-vpn.interfaceType = "tap";
    services.tinc.networks.simatime-vpn.hosts = import ./vpnHosts.nix;
    system.autoUpgrade.channel = "https://nixos.org/channels/nixos-19.09";
    system.autoUpgrade.dates = "03:00";
    system.autoUpgrade.enable = true;
    users.motd = "\n\n\twelcome to the simatime network\n\n\n";
    users.users =  import ./users.nix;
    users.mutableUsers = false;
  };
  os = nixos {
    system = "x86_64-linux";
    configuration = (defaults // configuration);
  };
in {
   system = os.system;
   vm = os.vm;
}