Move the function to generate the store path into lib.

flake.nix

@@ -6,7 +6,14 @@
   };
 
   outputs = { self, nixpkgs, flake-utils }: {
-    serviceConfig =
+    serviceConfig = self.lib.makeServiceConfig
+      [
+        "service-1"
+        "service-2"
+      ];
+
+    lib = {
+      makeServiceConfig = serviceNames:
         let
           system = flake-utils.lib.system.x86_64-linux;
           lib = nixpkgs.lib;
@@ -18,11 +25,7 @@
           services = lib.flip lib.genAttrs
             (serviceName:
               nixosConfig.config.systemd.units."${serviceName}.service".unit)
-          # TODO: generate this list from the config instead of hard coding
-          [
-            "service-1"
-            "service-2"
-          ];
+            serviceNames;
         in
         nixpkgs.legacyPackages.${system}.writeTextFile {
           name = "services";
@@ -30,4 +33,5 @@
           text = lib.generators.toJSON { } services;
         };
     };
+  };
 }