{
  inputs = {
    flake-utils.url = "github:numtide/flake-utils";
    nixpkgs.url = "github:nixos/nixpkgs/staging-next";
    nixpkgsMaster.url = "github:NixOS/nixpkgs/master";

    nur.url = "github:nix-community/NUR";

    home-manager = {
      url = "github:nix-community/home-manager/release-22.05";
      inputs.nixpkgs.follows = "nixpkgs";
    };

    nix-pre-commit-hooks = {
      url = "github:cachix/pre-commit-hooks.nix/master";
      inputs.flake-utils.follows = "flake-utils";
    };

    sops-nix = {
      url = "github:Mic92/sops-nix";
      inputs.nixpkgs.follows = "nixpkgs";
    };

    krops = {
      url = "github:Mic92/krops";
      inputs = {
        flake-utils.follows = "flake-utils";
        nixpkgs.follows = "nixpkgs";
      };
    };
  };
  outputs =
    { self
    , nixpkgs
    , flake-utils
    , krops
    , home-manager
    , nur
    , nix-pre-commit-hooks
    , ...
    }@inputs: flake-utils.lib.eachSystem [
      "x86_64-linux"
    ]
      (system:
      let
        pkgs = import nixpkgs { inherit system; };
        inherit (pkgs) lib;
      in
      {
        checks = {
          pre-commit-check = nix-pre-commit-hooks.lib.${system}.run {
            src = self;
            hooks = {
              black.enable = true;
              nixpkgs-fmt.enable = true;
              shellcheck.enable = true;
            };
          };
        };
        devShell = pkgs.mkShell {
          buildInputs = (with pkgs; [
            black
            just
            nixpkgs-fmt
            shellcheck
            sops
            ssh-to-age
          ]);

          shellHook = ''
            ${self.checks.${system}.pre-commit-check.shellHook}
          '';
        };

        apps = lib.mapAttrs
          (name: program: { type = "app"; program = toString program; })
          (flake-utils.lib.flattenTree {
            deploy = lib.recurseIntoAttrs (lib.mapAttrs
              (hostname: machine:
                let
                  inherit (krops.packages.${system}) writeCommand;
                  inherit (krops) lib;
                in
                writeCommand "deploy-${hostname}" {
                  target = lib.mkTarget "root@${machine.config.deployment.targetHost}" // {
                    extraOptions = [
                      # force allocation of tty to allow aborting with ^C and to show build progress
                      "-t"
                    ];
                  };
                  source = lib.evalSource (lib.singleton {
                    config.file = {
                      path = toString ./.;
                      useChecksum = true;
                    };
                  });
                  command = targetPath: ''
                    nixos-rebuild switch --flake ${targetPath}/config -L --keep-going
                  '';
                }
              )
              self.nixosConfigurations);

            showKeyFingerprint = pkgs.writeShellScript "show-key-fingerprint" ''
              ${pkgs.gnupg}/bin/gpg --with-fingerprint --with-colons --show-key "keys/''${1}.asc" | awk -F: '$1 == "fpr" { print $10; exit }'
            '';
          });

      }) // {
      overlay = import ./pkgs;

      nixosConfigurations = nixpkgs.lib.mapAttrs
        (hostname: { system
                   , extraModules ? [ ]
                   , targetHost ? hostname
                   , nixpkgs ? inputs.nixpkgs
                   }: nixpkgs.lib.nixosSystem rec {
          inherit system;
          specialArgs = { inherit self system; };

          modules = [
            (./hosts + "/${hostname}/configuration.nix")

            ./modules

            {
              _module.args.inputs = inputs;
            }

            # deployment settings
            ({ lib, ... }: {
              options.deployment = {
                targetHost = lib.mkOption {
                  type = lib.types.str;
                  readOnly = true;
                  internal = true;
                };
              };
              config.deployment = {
                inherit targetHost;
              };
            })
          ] ++ [{
            nixpkgs.overlays = [ nur.overlay ];
          }] ++ [
            home-manager.nixosModules.home-manager
          ] ++ (with inputs; [
            sops-nix.nixosModules.sops
          ]) ++ extraModules;
        })
        (import ./hosts inputs);
    };
}