let
  inherit (import ../default.nix { }) pkgs inputs;
  inherit (pkgs) lib;
  inherit (lib) mkOption;
  eval =
    module:
    (lib.evalModules {
      specialArgs = {
        inherit inputs;
      };
      modules = [
        module
        ./data-model.nix
      ];
    }).config;
  nixops4Deployment = inputs.nixops4.modules.nixops4Deployment.default;
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 =
                  { config, ... }:
                  {
                    _class = "fediversity-resource-policy";

                    options = {
                      extra-config = mkOption {
                        description = "Any options from NixOS";
                      };
                      apply = mkOption {
                        type = with types; functionTo raw;
                        default = requests: lib.mkMerge (requests ++ [ config.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 =
                  { config, ... }:
                  {
                    _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;
                      };
                      apply = mkOption {
                        type = with types; functionTo raw; # TODO: splice out the user type from NixOS
                        default =
                          requests:
                          let
                            # Filter out requests that need wheel if policy doesn't allow it
                            validRequests = lib.filterAttrs (_name: req: !req.wheel || config.wheel) requests;
                          in
                          lib.optionalAttrs (validRequests != { }) {
                            ${config.username} = {
                              isNormalUser = true;
                              packages = with lib; concatMap (request: attrValues request.packages) (attrValues validRequests);
                              extraGroups = lib.optional config.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";
                      };
                    };
                  implementation =
                    cfg:
                    lib.optionalAttrs cfg.enable {
                      dummy.login-shell.packages.hello = pkgs.hello;
                    };
                };
              environments.single-nixos-vm =
                { config, ... }:
                {
                  _class = "fediversity-environment";
                  resources.shell.login-shell.username = "operator";
                  implementation =
                    requests:
                    { providers, ... }:
                    {
                      _class = "nixops4Deployment";
                      providers = {
                        inherit (inputs.nixops4.modules.nixops4Provider) local;
                      };
                      resources.the-machine = {
                        _class = "nixops4Resource";
                        type = providers.local.exec;
                        imports = [
                          inputs.nixops4-nixos.modules.nixops4Resource.nixos
                        ];
                        nixos.module =
                          { ... }:
                          {
                            _class = "nixos";
                            users.users = config.resources.shell.login-shell.apply (
                              lib.filterAttrs (_name: value: value ? login-shell) requests
                            );
                          };
                      };
                    };
                };
            };
            options = {
              example-configuration = mkOption {
                type = config.configuration;
                readOnly = true;
                default = {
                  _class = "fediversity-configuration";
                  enable = true;
                  applications.hello.enable = true;
                };
              };
            };
            environments.single-nixos-vm = {

            };
            configurations.example = {
              enable = true;
              applications.hello.enable = 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;
    };
  };
}