nix/hm: add systemd.target in home-manager (#532)

* nix: add systemd.target

* fix: format

* Update README.md

* Update hm-module.nix

cf2b1d8405/example-units/hyprpaper.service (L19)

* fix

* Update README.md

README.md

@@ -213,7 +213,10 @@ For NixOS users, a home manager module is also available.
 ```nix
 programs.caelestia = {
   enable = true;
-  systemd.enable = false; # if you prefer starting from your compositor
+  systemd = {
+    enable = false; # if you prefer starting from your compositor
+    target = "graphical-session.target";
+  };
   settings = {
     bar.status = {
       showBattery = false;

nix/hm-module.nix

@@ -25,6 +25,13 @@ in {
           default = true;
           description = "Enable the systemd service for Caelestia shell";
         };
+        target = mkOption {
+          type = types.str;
+          description = ''
+            The systemd target that will automatically start the Caelestia shell.
+          '';
+          default = "graphical-session.target";
+        };
       };
       settings = mkOption {
         type = types.attrsOf types.anything;
@@ -65,8 +72,8 @@ in {
       systemd.user.services.caelestia = lib.mkIf cfg.systemd.enable {
         Unit = {
           Description = "Caelestia Shell Service";
-          After = ["graphical-session.target"];
-          PartOf = ["graphical-session.target"];
+          After = [cfg.systemd.target];
+          PartOf = [cfg.systemd.target];
           X-Restart-Triggers = lib.mkIf (cfg.settings != {}) [
             "${config.xdg.configFile."caelestia/shell.json".source}"
           ];
@@ -86,7 +93,7 @@ in {
         };
 
         Install = {
-          WantedBy = ["graphical-session.target"];
+          WantedBy = [cfg.systemd.target];
         };
       };