{ ipv4
, ipv6
, config
, optionalString
, concatStringsSep
, mapAttrsToList
, ...
}:
let
  port = 721;
  hosts = {
    cherry = "10.123.42.29";
    cream = "10.123.42.27";
    robi = "10.123.42.123";
    sternchen = "10.123.42.25";
    sterni = "10.123.42.24";
  };
  network = "secret";
in
{
  sops.secrets.tinc_ed25519_key = { };

  services.tinc.networks = {
    ${network} = {
      ed25519PrivateKeyFile = config.sops.secrets.tinc_ed25519_key.path;
      extraConfig = ''
        LocalDiscovery = yes
        Port = ${toString port}
      '';
      hostSettings = {
        sternchen = {
          subnets = [{ address = hosts.sternchen; }];
          settings.Ed25519PublicKey = "Z567IKl00Kw5JFBNwMvjL33QYe2hRoNtQcNIDFRPReB";
        };
        cream = {
          subnets = [{ address = hosts.cream; }];
          settings.Ed25519PublicKey = "Y/YRA90mAlNEmdhUWlUTHjjsco6d6hlvW11sPtarIdL";
        };
        cherry = {
          subnets = [{ address = hosts.cherry; }];
          settings.Ed25519PublicKey = "BsPIrZjbzn0aryC0HO3OXSb4oFCMmzNDmMDQmxUXUuC";
        };
        sterni = {
          subnets = [{ address = hosts.sterni; }];
          settings.Ed25519PublicKey = "r6mRDc814z2YtyG9ev/XXV2SgquqWR8n53V13xNXb7O";
        };
        robi = {
          addresses = [{ address = "144.76.13.147"; port = port; }];
          subnets = [{ address = hosts.robi; }];
          settings.Ed25519PublicKey = "bZUbSdME4fwudNVbUoNO7PpoOS2xALsyTs81F260KbL";
        };
      };
    };
  };

  systemd.network.enable = true;
  systemd.network.networks.${network}.extraConfig = ''
    [Match]
    Name = tinc.${network}
    [Link]
    # tested with `ping -6 turingmachine.r -s 1378`, not sure how low it must be
    MTUBytes=1377
    [Network]
    ${optionalString (ipv4 != null) "Address=${ipv4}/24"}
    ${optionalString (ipv6 != null) "Address=${ipv6}/28"}
    RequiredForOnline = no
    LinkLocalAddressing = no
  '';

  networking.extraHosts = concatStringsSep "\n" (mapAttrsToList (name: ip: "${ip} ${name}.${network}") hosts);

  services.openssh.knownHosts = {
    "cream.${network}" = {
      hostNames = [ "cream.${network}" hosts.cream ];
      publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIConHiCL7INgAhuN6Z9TqP0zP+xNpdV7+OHwUca4IRDD";
    };
    "sternchen.${network}" = {
      hostNames = [ "sterni.${network}" hosts.sterni ];
      publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAILriD/0+65L1mkbjKENwpvB3wUMXz/rEf9J8wuJjJa0q";
    };
    "sterni.${network}" = {
      hostNames = [ "sterni.${network}" hosts.sterni ];
      publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIEQRH4gzT4vWSx3KN80ePPYhSPZRUae/qSyEym6pJTht";
    };
    "robi" = {
      hostNames = [ "robi.${network}" hosts.robi ];
      publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIK2PGX6cZuBUGX4VweMzi0aRh4uQ61yngCzZGcK3w5XV";
    };
  };

}