way-displays-stateful: add module

Author: mightyiam

modules/modules.nix

@@ -471,6 +471,7 @@ let
       ./services/unison.nix
       ./services/vdirsyncer.nix
       ./services/volnoti.nix
+      ./services/way-displays-stateful.nix
       ./services/way-displays.nix
       ./services/wayvnc.nix
       ./services/window-managers/awesome.nix

modules/services/way-displays-stateful.nix

@@ -0,0 +1,45 @@
+{
+  lib,
+  pkgs,
+  config,
+  ...
+}:
+let
+  cfg = config.services.way-displays-stateful;
+in
+{
+  meta.maintainers = [ lib.maintainers.mightyiam ];
+
+  options.services.way-displays-stateful = {
+    enable = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      description = ''
+        A stateful way-displays setup where the configuration file is not linked to the store.
+        This allows using `way-displays --set <arguments>` and then `way-displays --write`.
+
+        A way-displays service is _not_ started automatically. Instead, a window manager should execute `systemctl --user start "way-displays@$XDG_VTNR".service` on startup.
+      '';
+    };
+    package = lib.mkPackageOption pkgs "way-displays" { };
+  };
+
+  config = {
+    assertions = [
+      (lib.hm.assertions.assertPlatform "services.way-displays-stateful" pkgs lib.platforms.linux)
+    ];
+
+    home.packages = [ cfg.package ];
+
+    systemd.user.services."way-displays@" = {
+      Unit.Description = "way-displays XDG_VTNR=%i";
+
+      Service = {
+        Environment = "XDG_VTNR=%i";
+        ExecStart = lib.getExe cfg.package;
+        Restart = "on-failure";
+        RestartSec = "10";
+      };
+    };
+  };
+}