{ hostName, config, lib, ... }:

let
  upstreamInterfaces =
    lib.filterAttrs (_: { upstream, ... }: upstream != null)
      config.site.hosts.${hostName}.interfaces;
  firstUpstreamInterface =
    if builtins.length (builtins.attrNames upstreamInterfaces) > 0
    then builtins.head (
      builtins.attrNames upstreamInterfaces
    )
    else null;
in
{
  systemd.network.networks = builtins.mapAttrs (_: { upstream, ... }: {
    DHCP = "yes";

    extraConfig = ''
      [CAKE]
      Parent = root
      # DOCSIS overhead
      OverheadBytes = 18
      Bandwidth = ${toString upstream.upBandwidth}K
    '';
  }) upstreamInterfaces;

  networking.nat = lib.optionalAttrs (firstUpstreamInterface != null) {
    enable = true;
    internalInterfaces = [ "core" ];
    externalInterface = firstUpstreamInterface;
    forwardPorts = config.site.hosts.${hostName}.forwardedPorts;
  };
}