Updated repo to make it a Nix Flake

flake.nix

@@ -0,0 +1,36 @@
+{
+  description = "An Invoice Ninja package and a module which can be added to a NixOS configuration";
+
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-24.11";
+
+  outputs =
+    { self, nixpkgs, nix, }:
+    let
+      systems = [ "x86_64-linux" ];
+      forEachSystem = nixpkgs.lib.genAttrs systems;
+
+      overlayList = [ self.overlays.default ];
+
+      pkgsBySystem = forEachSystem (
+        system:
+        import nixpkgs {
+          inherit system;
+          overlays = overlayList;
+        }
+      );
+
+    in
+    rec {
+
+      # A Nixpkgs overlay that provides a 'Invoice Ninja' package.
+      overlays.default = final: prev: { invoice-ninja = final.callPackage ./package.nix { }; };
+
+      packages = forEachSystem (system: {
+        invoice-ninja = pkgsBySystem.${system}.invoice-ninja;
+        default = pkgsBySystem.${system}.invoice-ninja;
+      });
+
+      nixosModules = import ./nixos-module { overlays = overlayList; };
+
+    };
+}

nixos-module/default.nix

@@ -0,0 +1,11 @@
+{ overlays }:
+
+{
+  invoice-ninja = import ./invoice-ninja.nix
+  overlayNixpkgsForThisInstance = 
+    { pkgs, ... }: {
+      nixpkgs = {
+        inherit overlays;
+      };
+    };
+};

nixos-module/invoice-ninja.nix

@@ -10,7 +10,7 @@ let
   cfg = config.services.invoice-ninja;
   user = cfg.user;
   group = cfg.group;
-  invoice-ninja = pkgs.callPackage ../../../../pkgs/by-name/in/invoice-ninja/package.nix {
+  invoice-ninja = pkgs.callPackage ../package.nix {
     inherit (cfg) dataDir runtimeDir;
   };
   configFormat = pkgs.formats.keyValue { };