{ overlay }:

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

with lib;
{
  options.services.madd-client = {
    enable = mkEnableOption "MADD client";
    endpoint = mkOption {
      type = types.str;
      description = "Endpoint for MADD client to connect to.";
    };
    interface = mkOption {
      type = types.str;
      default = "eth0";
      description = "Network interface to use for MADD client.";
    };
    priv-key-file = mkOption {
      type = types.str;
      default = "/etc/ssh/ssh_host_ed25519_key";
      description = "Path to the private SSH key file identifying this machine.";
    };
    pub-key-file = mkOption {
      type = types.str;
      default = "${config.services.madd-client.priv_key_file}.pub";
      description = "Path to the public SSH key file identifying this machine.";
    };
    hostname = mkOption {
      type = types.str;
      default = config.networking.hostName;
      description = "Hostname to use for MADD client.";
    };
  };

  options.services.madd-server = {
    enable = mkEnableOption "MADD server";
  };

  config = {
    nixpkgs.overlays = [ overlay ];
  }
  // (
    let
      cfg = config.services.madd-client;
    in
    optionalAttrs config.madd-client.enable {
      systemd.services.madd-client = {
        description = "MADD Client Service";
        wantedBy = [ "multi-user.target" ];
        before = [ "network-pre.target" ];
        requires = [ "network-pre.target" ];
        script = ''
          ${pkgs.iproute2}/bin/ip -4 monitor address label dev "${cfg.interface}" | while read -r event; do
            if [[ $event == \[ADDR\]* ]]; then
              ipv4=$(${pkgs.iproute2}/bin/ip -4 addr show dev "${cfg.interface}" | grep -Po 'inet \K[\d.]+')
              if [ -n "$ipv4" ]; then

                export MADD_ENDPOINT="${cfg.endpoint}"
                export MADD_PRIV_KEY="${cfg.priv-key-file}"
                export MADD_PUB_KEY="${cfg.pub-key-file}"
                export MADD_HOSTNAME="${cfg.hostname}"
                export MADD_IP="$ipv4"

                ${pkgs.madd-client}/bin/madd-client
              fi
          done
        '';
      };
    }
  )
  // (optionalAttrs config.madd-server.enable {
  });
}