{
  description = "Upgrade NixOS system (and/or home-manager) in the background, with notification support";

  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
  inputs.poetry2nix.url = "github:nix-community/poetry2nix";

  outputs = {
    self,
    nixpkgs,
    poetry2nix,
  }: let
    supportedSystems = ["x86_64-linux" "x86_64-darwin" "aarch64-linux" "aarch64-darwin"];
    forAllSystems = nixpkgs.lib.genAttrs supportedSystems;
    pkgs = forAllSystems (system: nixpkgs.legacyPackages.${system});
  in {
    packages = forAllSystems (system: let
      inherit (poetry2nix.lib.mkPoetry2Nix {pkgs = pkgs.${system};}) mkPoetryApplication;
    in {
      default = mkPoetryApplication {
        projectDir = self;
        checkGroups = [];
      };
    });

    apps = forAllSystems (system: {
      default = {
        type = "app";
        program = "${self.packages.${system}.default}/bin/nix-background-upgrade";
      };
    });

    devShells = forAllSystems (system: {
      default = import ./shell.nix {
        pkgs = pkgs.${system};
        inherit (poetry2nix.lib.mkPoetry2Nix {pkgs = pkgs.${system};}) mkPoetryEnv;
      };
    });
  };
}