let
  inherit (import ../default.nix { }) pkgs inputs;
  inherit (pkgs) lib;
  inherit (lib) mkOption types;
  eval =
    module:
    (lib.evalModules {
      specialArgs = {
        inherit inputs;
      };
      modules = [
        module
        ./data-model.nix
      ];
    }).config;
in
{
  _class = "nix-unit";

  test-eval = {
    expr =
      let
        fediversity = eval (
          { config, ... }:
          {
            _class = "fediversity-settings";
            config = {
              resources.nixos-configuration = {
                description = "An entire NixOS configuration";
                request =
                  { ... }:
                  {
                    _class = "fediversity-resource-request";
                    options.config = mkOption {
                      description = "Any options from NixOS";
                    };
                  };

                policy =
                  { ... }:
                  {
                    _class = "fediversity-resource-policy";

                    options = {
                      extra-config = mkOption {
                        description = "Any options from NixOS";
                      };
                    };
                    config = {
                      resource-type = types.raw; # TODO: what's the type of a NixOS configuration?
                      apply = policy: requests: lib.mkMerge (requests ++ [ policy.extra-config ]);
                    };
                  };
              };
              resources.login-shell = {
                _class = "fediversity-resource";
                description = "The operator needs to be able to log into the shell";
                request =
                  { ... }:
                  {
                    _class = "fediversity-resource-request";
                    options = {
                      wheel = mkOption {
                        description = "Whether the login user needs root permissions";
                        type = types.bool;
                        default = false;
                      };
                      packages = mkOption {
                        description = "Packages that need to be available in the user environment";
                        type = with types; attrsOf package;
                      };
                    };
                  };
                policy =
                  { ... }:
                  {
                    _class = "fediversity-resource-policy";
                    options = {
                      username = mkOption {
                        description = "Username for the operator";
                        type = types.str; # TODO: use the proper constraints from NixOS
                      };
                      wheel = mkOption {
                        description = "Whether to allow login with root permissions";
                        type = types.bool;
                        default = false;
                      };
                    };
                    config = {
                      resource-type = types.raw; # TODO: splice out the user type from NixOS
                      apply =
                        policy: requests:
                        let
                          # Filter out requests that need wheel if policy doesn't allow it
                          validRequests = lib.filterAttrs (_name: req: !req.wheel || policy.wheel) requests;
                        in
                        lib.optionalAttrs (validRequests != { }) {
                          ${policy.username} = {
                            isNormalUser = true;
                            packages = with lib; concatMap (request: attrValues request.packages) (attrValues validRequests);
                            extraGroups = lib.optional policy.wheel "wheel";
                          };
                        };
                    };
                  };
              };
              applications.hello =
                { ... }:
                {
                  _class = "fediversity-application";
                  description = ''Command-line tool that will print "Hello, world!" on the terminal'';
                  module =
                    { ... }:
                    {
                      _class = "fediversity-application-config";
                      options = {
                        enable = lib.mkEnableOption "Hello in the shell";
                      };
                    };
                  resources =
                    cfg:
                    lib.optionalAttrs cfg.enable {
                      hello.login-shell.packages = {
                        inherit (pkgs) hello;
                      };
                    };
                };
              environments.single-nixos-vm = environment: {
                _class = "fediversity-environment";
                resources.shell.login-shell = {
                  username = "operator";
                  wheel = false; # FIXME: default needs the type uncommented
                };
                implementation = requests: {
                  _class = "nixos";
                  users.users = (
                    config.resources.login-shell.policy.apply environment.config.resources.shell.login-shell (
                      lib.concatMapAttrs (
                        _application: resources:
                        lib.mapAttrs (_k: lib.getAttr "login-shell") (
                          lib.filterAttrs (_name: value: value ? login-shell) resources
                        )
                      ) requests
                    )
                  );
                };
              };
            };
            options = {
              example-configuration = mkOption {
                type = config.configuration;
                readOnly = true;
                default = {
                  _class = "fediversity-configuration";
                  enable = true;
                  applications.hello.enable = true;
                };
              };
              example-deployment = mkOption {
                type = types.raw;
                readOnly = true;
                default = config.environments.single-nixos-vm.deployment config.example-configuration;
              };
            };
          }
        );
      in
      {
        inherit (fediversity)
          example-configuration
          ;
        num-packages = lib.lists.length fediversity.example-deployment.users.users.operator.packages;
      };
    expected = {
      example-configuration = {
        enable = true;
        applications.hello.enable = true;
      };
      num-packages = 1;
    };
  };
}