{
  description = "A Python Project Template.";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
  };

  outputs =
    {
      self,
      nixpkgs,
      ...
    }@inputs:
    let
      supportedSystems = [ "x86_64-linux" ];
      forAllSystems = nixpkgs.lib.genAttrs supportedSystems;
      pkgs = forAllSystems (system: nixpkgs.legacyPackages.${system});
    in
    {
      # `nix build`
      packages = forAllSystems (system: rec {
        default = cloudns;
        cloudns = pkgs.${system}.callPackage ./nix/package.nix { src = ./.; };
      });

      # `nix develop`
      devShells = forAllSystems (system: rec {
        default = venv;

        venv = pkgs.${system}.mkShell {
          shellHook = ''
            if [ ! -d .venv/ ]; then
              echo "Creating Virtual Environment..."
              ${pkgs.${system}.python3}/bin/python3 -m venv .venv
            fi

            alias activate='source .venv/bin/activate'

            echo "Entering Virtual Environment..."
            source .venv/bin/activate
          '';
        };
      });

      # NixOS Module
      nixosModules.default = import ./nix/module.nix inputs;
    };
}