nix flake complete, added alternative data storage option

flake.nix

@@ -1,5 +1,5 @@
 {
-  description = "Install main.py to data directory with dependencies";
+  description = "py2fa-gtk packaged the Nix way";
 
   inputs.nixpkgs.url = "github:nixos/nixpkgs/nixos-25.11";
 
@@ -7,11 +7,8 @@
     let
       system = "x86_64-linux";
       pkgs = nixpkgs.legacyPackages.${system};
-      packageName = "py2fa-gtk";
-      scriptSource = ./src/main.py;
 
-      # 1. Define Python environment
-      python = pkgs.python312.withPackages (ps: with ps; [
+      pythonEnv = pkgs.python312.withPackages (ps: with ps; [
         cryptography 
         opencv-python 
         pygobject3 
@@ -19,52 +16,51 @@
         pyzbar
       ]);
 
-      # 2. Define libraries for ZBar (shared object)
-      zbarLibs = [ pkgs.zbar ];
+      runtimeLibs = with pkgs; [ 
+        gtk3 
+        zbar 
+        gobject-introspection
+      ];
 
     in
     {
       packages.${system}.default = pkgs.stdenv.mkDerivation {
-        name = packageName;
+        name = "py2fa-gtk";
         
-        nativeBuildInputs = [ pkgs.wrapGAppsHook3 ];
+        src = ./src; 
 
-        buildInputs = with pkgs; [
-          gtk3
-          pango
-          gdk-pixbuf
-          atk
-          cairo
-          gobject-introspection
-          # Python env included here so the wrapper knows about it
-          python
-        ] ++ zbarLibs;
+        nativeBuildInputs = [
+          pkgs.wrapGAppsHook3
+          pkgs.makeWrapper
+        ];
 
-        dontUnpack = true;
+        buildInputs = runtimeLibs ++ [ pythonEnv ];
+
+        dontBuild = true;
 
         installPhase = ''
-          mkdir -p $out/bin
+          runHook preInstall
 
-          cat > $out/bin/${packageName} <<EOF
-#!/bin/sh
-export LD_LIBRARY_PATH="${pkgs.lib.makeLibraryPath zbarLibs}:\$LD_LIBRARY_PATH"
+          # A. Create standard directory structure in the Nix Store
+          mkdir -p $out/bin $out/share/py2fa-gtk
           
-TARGET_DIR="\$HOME/.local/share/${packageName}"
-TARGET_FILE="\$TARGET_DIR/main.py"
+          # B. Copy the python script to the store (Read-Only)
+          cp main.py $out/share/py2fa-gtk/main.py
 
-mkdir -p "\$TARGET_DIR"
+          # 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 ]}"
 
-if [ ! -f "\$TARGET_FILE" ]; then
-  echo "Installing main.py to \$TARGET_FILE..."
-  cp "${scriptSource}" "\$TARGET_FILE"
-  chmod +w "\$TARGET_FILE"
-fi
-
-exec ${python}/bin/python3 "\$TARGET_FILE" "\$@"
-EOF
-          
-          chmod +x $out/bin/${packageName}
+          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).
       };
     };
 }