{
  description = "ZUGFeRD REST API Service";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    flake-utils.url = "github:numtide/flake-utils";

    m3ta-nixpkgs.url = "git+https://code.m3ta.dev/m3tam3re/nixpkgs";
    agents = {
      url = "git+https://code.m3ta.dev/m3tam3re/AGENTS";
      flake = false;
    };
  };

  outputs = {
    self,
    nixpkgs,
    flake-utils,
    m3ta-nixpkgs,
    agents,
  }:
    {
      nixosModules.default = import ./nix/module.nix;
    }
    // flake-utils.lib.eachDefaultSystem (system: let
      pkgs = nixpkgs.legacyPackages.${system};
      pythonPackages = pkgs.python311Packages;

      # factur-x package - not available in nixpkgs, so we package it inline
      factur-x = pythonPackages.buildPythonPackage rec {
        pname = "factur_x";
        version = "3.8";
        format = "pyproject";

        src = pythonPackages.fetchPypi {
          inherit pname version;
          hash = "sha256-/pNY5w09pxcGAFFh3USTkLlkGr+JOTUqhglYzNMByks=";
        };

        nativeBuildInputs = with pythonPackages; [
          hatchling
          hatch-requirements-txt
        ];

        dependencies = with pythonPackages; [pypdf lxml];

        pythonRelaxDeps = true;

        meta = {
          description = "Python library to generate and read Factur-X invoices";
          license = pkgs.lib.licenses.mit;
        };
      };

      zugferd-service = pythonPackages.buildPythonApplication {
        pname = "zugferd-service";
        version = "1.0.0";
        pyproject = true;
        src = ./.;

        pythonRelaxDeps = true;

        build-system = [pythonPackages.hatchling];

        dependencies = with pythonPackages; [
          fastapi
          uvicorn
          pydantic
          python-multipart
          factur-x
          pypdf
          lxml
        ];

        nativeCheckInputs = with pythonPackages; [
          pytestCheckHook
          pytest-asyncio
          httpx
        ];

        passthru = {mainProgram = "zugferd-service";};

        meta = {
          description = "REST API for ZUGFeRD invoice extraction";
          license = pkgs.lib.licenses.mit;
        };
      };

      m3taLib = m3ta-nixpkgs.lib.x86_64-linux;
      rules = m3taLib.opencode-rules.mkOpencodeRules {
        inherit agents;
        languages = ["python"];
      };
    in {
      packages.default = zugferd-service;
      packages.zugferd-service = zugferd-service;

      devShells.default = pkgs.mkShell {
        packages = [
          (pkgs.python311.withPackages (ps:
            with ps; [
              fastapi
              uvicorn
              pydantic
              python-multipart
              pypdf
              lxml
              pytest
              pytest-asyncio
              httpx
              factur-x
              # factur-x - install via pip if not available
            ]))
          pkgs.python311Packages.pip
        ];

        inherit (rules) instructions;
        shellHook = ''
          ${rules.shellHook}
        '';
      };
    });
}