nixos/networkd-dispatcher: add rules option

nixos/modules/services/networking/networkd-dispatcher.nix

@@ -3,8 +3,11 @@
 with lib;
 
 let
+
   cfg = config.services.networkd-dispatcher;
+
 in {
+
   options = {
     services.networkd-dispatcher = {
 
@@ -14,14 +17,49 @@ in {
         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.
+              '';
+            };
+          };
+        });
       };
 
     };
@@ -30,34 +68,31 @@ in {
   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 - -"
-      ];
-
     };
 
-
   };
 }