{

  inputs = {
    naersk.url = "github:nmattia/naersk/master";
    naersk.inputs.nixpkgs.follows = "nixpkgs";
    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
    utils.url = "github:numtide/flake-utils";
  };

  outputs = { self, nixpkgs, utils, naersk }:
    utils.lib.eachDefaultSystem (system:
      let
        pkgs = import nixpkgs { inherit system; };
        naersk-lib = pkgs.callPackage naersk { };
      in {

        defaultPackage = naersk-lib.buildPackage {
          src = ./.;
          buildInputs = with pkgs; [ pkg-config openssl ];
        };

        defaultApp = utils.lib.mkApp { drv = self.defaultPackage."${system}"; };

        devShell = with pkgs;
          mkShell {
            buildInputs = [
              # rust
              cargo
              cargo-watch
              rustc
              rust-analyzer
              rustfmt
              rustPackages.clippy

              # system
              pkg-config
              openssl
              cmake

              # dhall
              dhall
              dhall-json

              jo
            ];
            RUST_LOG = "info";
            RUST_SRC_PATH = rustPlatform.rustLibSrc;
          };

        nixosModules.bot = { config, lib, ... }: {
          options.within.services.mara-bot.enable =
            lib.mkEnableOption "enable Mara bot";

          config = lib.mkIf config.within.services.mara-bot.enable {
            users.groups.mara-bot = { };

            users.users.mara-bot = {
              createHome = true;
              isSystemUser = true;
              home = "/var/lib/mara-bot";
              group = "mara-bot";
            };

            systemd.services.mara-bot = {
              wantedBy = [ "multi-user.target" ];
              environment.RUST_LOG = "tower_http=debug,info";
              unitConfig.ConditionPathExists = "/var/lib/mara-bot/config.yaml";
              serviceConfig = {
                User = "mara-bot";
                Group = "mara-bot";
                Restart = "always";
                WorkingDirectory = "/var/lib/mara-bot";
                ExecStart = "${self.defaultPackage."${system}"}/bin/mara";
              };
            };
          };
        };
      });
}