{ config, pkgs, lib, ... }:

let
  # Filter interfaces that have a specific speed set
  speedInterfaces = lib.filter (i: i.speed != null) config.vars.interfaces;
  
  # Find the interface designated as the "primary" (first one with an IP) for the gateway
  # If none have IPs, we just pick the first interface in the list
  primaryInterface = lib.findFirst (i: i.ip != null) (lib.head config.vars.interfaces) config.vars.interfaces;

in
{
  networking.hostName = config.vars.hostname;
  networking.hostId = config.vars.hostid;
  
  # Global DNS settings
  networking.nameservers = [ "192.168.178.10" "9.9.9.9" ];
  
  # Default Gateway
  networking.defaultGateway = {
    address = "192.168.178.1";
    interface = primaryInterface.name;
  };

  # 1. Generate Static IP Configurations
  networking.interfaces = lib.listToAttrs (map (iface: {
    name = iface.name;
    value = {
      # If an IP is provided, use it. Otherwise empty list.
      ipv4.addresses = if iface.ip != null then [{
        address = iface.ip;
        prefixLength = iface.prefixLength;
      }] else [];

      # Logic: If we have a static IP, disable DHCP. If no IP, enable DHCP.
      useDHCP = (iface.ip == null);
    };
  }) config.vars.interfaces);


  # 2. Systemd Service for Link Speed
  systemd.services.force-interface-speeds = lib.mkIf (speedInterfaces != []) {
    description = "Force link speed on configured interfaces";
    wantedBy = [ "network-pre.target" ];
    before = [ "network-pre.target" ];
  serviceConfig = {
    Type = "oneshot";
    ExecStart = pkgs.writeShellScript "force-interface-speeds" (
      lib.concatMapStringsSep "\n" (iface: ''
        ${pkgs.ethtool}/bin/ethtool -s ${iface.name} speed ${toString iface.speed} duplex full autoneg on
        ${pkgs.ethtool}/bin/ethtool --set-eee ${iface.name} eee off || true
        '') speedInterfaces
      );
    };
  };
}