nixos/networkd-dispatcher: add rules option

with lib;

let

  cfg = config.services.networkd-dispatcher;

in {

  options = {

    services.networkd-dispatcher = {

        for usage.

      '');

      scriptDir = mkOption {

        type = types.path;

        default = "/var/lib/networkd-dispatcher";

        description = mdDoc ''

          This directory is used for keeping various scripts read and run by

          networkd-dispatcher. See [https://gitlab.com/craftyguy/networkd-dispatcher](upstream instructions)

          for directory structure and script usage.

      rules = mkOption {

        default = {};

        example = lib.literalExpression ''

          { "restart-tor" = {

              onState = ["routable" "off"];

              script = '''

                #!''${pkgs.runtimeShell}

                if [[ $IFACE == "wlan0" && $AdministrativeState == "configured" ]]; then

                  echo "Restarting Tor ..."

                  systemctl restart tor

                fi

                exit 0

              ''';

            };

          };

        '';

        description = lib.mdDoc ''

          Declarative configuration of networkd-dispatcher rules. See

          [https://gitlab.com/craftyguy/networkd-dispatcher](upstream instructions)

          for an introduction and example scripts.

        '';

        type = types.attrsOf (types.submodule {

          options = {

            onState = mkOption {

              type = types.listOf (types.enum [

                "routable" "dormant" "no-carrier" "off" "carrier" "degraded"

                "configuring" "configured"

              ]);

              default = null;

              description = lib.mdDoc ''

                List of names of the systemd-networkd operational states which

                should trigger the script. See <https://www.freedesktop.org/software/systemd/man/networkctl.html>

                for a description of the specific state type.

              '';

            };

            script = mkOption {

              type = types.lines;

              description = lib.mdDoc ''

                Shell commands executed on specified operational states.

              '';

            };

          };

        });

      };

    };

  };

  config = mkIf cfg.enable {

    systemd = {

      packages = [ pkgs.networkd-dispatcher ];

      services.networkd-dispatcher = {

        wantedBy = [ "multi-user.target" ];

        # Override existing ExecStart definition

        serviceConfig.ExecStart = [

        serviceConfig.ExecStart = let

          scriptDir = pkgs.symlinkJoin {

            name = "networkd-dispatcher-script-dir";

            paths = lib.mapAttrsToList (name: cfg:

              (map(state:

                pkgs.writeTextFile {

                  inherit name;

                  text = cfg.script;

                  destination = "/${state}.d/${name}";

                  executable = true;

                }

              ) cfg.onState)

            ) cfg.rules;

          };

        in [

          ""

          "${pkgs.networkd-dispatcher}/bin/networkd-dispatcher -v --script-dir ${cfg.scriptDir} $networkd_dispatcher_args"

          "${pkgs.networkd-dispatcher}/bin/networkd-dispatcher -v --script-dir ${scriptDir} $networkd_dispatcher_args"

        ];

      };

      # Directory structure required according to upstream instructions

      # https://gitlab.com/craftyguy/networkd-dispatcher

      tmpfiles.rules = [

        "d '${cfg.scriptDir}'               0750 root root - -"

        "d '${cfg.scriptDir}/routable.d'    0750 root root - -"

        "d '${cfg.scriptDir}/dormant.d'     0750 root root - -"

        "d '${cfg.scriptDir}/no-carrier.d'  0750 root root - -"

        "d '${cfg.scriptDir}/off.d'         0750 root root - -"

        "d '${cfg.scriptDir}/carrier.d'     0750 root root - -"

        "d '${cfg.scriptDir}/degraded.d'    0750 root root - -"

        "d '${cfg.scriptDir}/configuring.d' 0750 root root - -"

        "d '${cfg.scriptDir}/configured.d'  0750 root root - -"

      ];

    };

  };

}