# flake.nix
{
  description = "Dev shell + runnable app for merge_pdfs.py";

  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-24.05";

  outputs = { self, nixpkgs }:
  let
    systems = [ "x86_64-linux" "aarch64-linux" "x86_64-darwin" "aarch64-darwin" ];
    forEachSystem = f: nixpkgs.lib.genAttrs systems (system:
      let
        pkgs = import nixpkgs { inherit system; };
        python = pkgs.python311.withPackages (ps: [ ps.pypdf2 ]);
        # Small wrapper so `nix run` works: it uses the Python with PyPDF2 and your script.
        merge-pdfs = pkgs.writeShellScriptBin "merge-pdfs" ''
          exec ${python}/bin/python ${./merge_pdfs.py} "$@"
        '';
      in f pkgs python merge-pdfs
    );
  in {
    devShells = forEachSystem (pkgs: python: merge-pdfs: {
      default = pkgs.mkShell {
        packages = [
          python            # Python 3.11 with PyPDF2
          pkgs.ruff         # optional: linter
          pkgs.pyright      # optional: type checker
        ];
        shellHook = ''
          echo "✅ Dev shell ready. Try:"
          echo "  python merge_pdfs.py output.pdf a.pdf b.pdf"
        '';
      };
    });

    # `nix run` makes it easy to use from anywhere:
    apps = forEachSystem (pkgs: python: merge-pdfs: {
      default = {
        type = "app";
        program = "${merge-pdfs}/bin/merge-pdfs";
      };
    });

    # expose the tiny wrapper as a package if you want `nix build .#merge-pdfs`
    packages = forEachSystem (pkgs: python: merge-pdfs: {
      default = merge-pdfs;
      merge-pdfs = merge-pdfs;
    });
  };
}