nixos/xscreensaver: add service to handle events

nix/nixosModules/common/xscreensaver.nix

@@ -0,0 +1,48 @@
+#
+# This module provides a service react to xscreensaver events
+#
+{
+  config,
+  lib,
+  ...
+}: let
+  cfg = config.services.xscreensaver;
+in {
+  options = {
+    services.xscreensaver.hooks = lib.mkOption {
+      type = with lib.types; attrsOf str;
+      description = "An attrset of events mapped a block of shell command to be run";
+      default = {};
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    systemd.user.services = {
+      "xscreensaver-hooks" = {
+        description = "Run commands on xscreensaver events";
+        after = ["graphical-session.target" "xscreensaver.service"];
+        partOf = ["graphical-session.target"];
+        wantedBy = ["graphical-session.target"];
+        script = let
+          handlers =
+            lib.concatMapAttrsStringSep "\n" (event: action: ''
+              "${event}")
+                      ( ${action}
+                      )
+                      ;;
+            '')
+            cfg.hooks;
+        in ''
+          xscreensaver-command -watch | while read event rest; do
+            case $event in
+              ${handlers}
+            esac
+          done
+        '';
+        path = [
+          cfg.package # contains xscreensaver-command
+        ];
+      };
+    };
+  };
+}