{
  description = "py2fa-gtk packaged the Nix way";

  inputs.nixpkgs.url = "github:nixos/nixpkgs/nixos-25.11";

  outputs = { self, nixpkgs }:
    let
      system = "x86_64-linux";
      pkgs = nixpkgs.legacyPackages.${system};

      pythonEnv = pkgs.python312.withPackages (ps: with ps; [
        cryptography 
        opencv-python 
        pygobject3 
        pyotp 
        pyzbar
      ]);

      runtimeLibs = with pkgs; [ 
        gtk3 
        zbar 
        gobject-introspection
      ];

    in
    {
      packages.${system}.default = pkgs.stdenv.mkDerivation {
        name = "py2fa-gtk";
        
        src = ./src; 

        nativeBuildInputs = [
          pkgs.wrapGAppsHook3
          pkgs.makeWrapper
        ];

        buildInputs = runtimeLibs ++ [ pythonEnv ];

        dontBuild = true;

        installPhase = ''
          runHook preInstall

          # A. Create standard directory structure in the Nix Store
          mkdir -p $out/bin $out/share/py2fa-gtk
          
          # B. Copy the python script to the store (Read-Only)
          cp main.py $out/share/py2fa-gtk/main.py

          # C. Create the binary executable
          # We wrap the python executable. 
          # 1. We tell it to run our specific script.
          # 2. We inject the ZBar library path so pyzbar works.
          makeWrapper ${pythonEnv}/bin/python3 $out/bin/py2fa-gtk \
            --add-flags "$out/share/py2fa-gtk/main.py" \
            --prefix LD_LIBRARY_PATH : "${pkgs.lib.makeLibraryPath [ pkgs.zbar ]}"

          runHook postInstall
        '';

        # wrapGAppsHook runs automatically after installPhase.
        # It will see the binary in $out/bin/py2fa-gtk and double-wrap it
        # to inject XDG_DATA_DIRS and GI_TYPELIB_PATH (fixing Pango/GTK).
      };
    };
}