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;
  nixops4Deployment = inputs.nixops4.modules.nixops4Deployment.default;
  inherit (inputs.nixops4.lib) mkDeployment;
in
{
  _class = "nix-unit";

  test-eval = {
    /**
      This tests a very simple arrangement that features all ingredients of the Fediversity business logic:
      application, resource, environment, deployment; and wires it all up in one end-to-end exercise.
      - The dummy resource is a login shell made available for some user.
      - The dummy application is `hello` that requires a shell to be deployed.
      - The dummy environment is a single NixOS VM that hosts one login shell, for the operator.
      - The dummy configuration enables the `hello` application.
      This will produce a NixOps4 deployment for a NixOS VM with a login shell for the operator and `hello` available.
    */
    expr =
      let
        fediversity = eval (
          { config, ... }:
          {
            config = {
              resources.login-shell = {
                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;
                      };
                    };
                    config = {
                      resource-type = types.raw; # TODO: splice out the user type from NixOS
                      apply =
                        requests:
                        let
                          # Filter out requests that need wheel if policy doesn't allow it
                          validRequests = lib.filterAttrs (
                            _name: req: !req.login-shell.wheel || config.wheel
                          ) requests.resources;
                        in
                        lib.optionalAttrs (validRequests != { }) {
                          ${config.username} = {
                            isNormalUser = true;
                            packages =
                              with lib;
                              attrValues (concatMapAttrs (_name: request: request.login-shell.packages) validRequests);
                            extraGroups = lib.optional config.wheel "wheel";
                          };
                        };
                    };
                  };
              };
              applications.hello =
                { ... }:
                {
                  description = ''Command-line tool that will print "Hello, world!" on the terminal'';
                  module =
                    { ... }:
                    {
                      options.enable = lib.mkEnableOption "Hello in the shell";
                    };
                  implementation = cfg: {
                    input = cfg;
                    output = lib.optionalAttrs cfg.enable {
                      resources.hello.login-shell.packages.hello = pkgs.hello;
                    };
                  };
                };
              environments.single-nixos-vm =
                { config, ... }:
                {
                  resources.operator-environment.login-shell.username = "operator";
                  implementation = requests: {
                    input = requests;
                    output =
                      { providers, ... }:
                      {
                        providers = {
                          inherit (inputs.nixops4.modules.nixops4Provider) local;
                        };
                        resources.the-machine = {
                          type = providers.local.exec;
                          imports = [
                            inputs.nixops4-nixos.modules.nixops4Resource.nixos
                          ];
                          nixos.module =
                            { ... }:
                            {
                              users.users = config.resources.operator-environment.login-shell.apply (
                                lib.filterAttrs (_name: value: value ? login-shell) requests
                              );
                            };
                        };
                      };
                  };
                };
            };
            options = {
              example-configuration = mkOption {
                type = config.configuration;
                readOnly = true;
                default = {
                  enable = true;
                  applications.hello.enable = true;
                };
              };
              example-deployment = mkOption {
                type = types.submodule nixops4Deployment;
                readOnly = true;
                default = config.environments.single-nixos-vm.deployment config.example-configuration;
              };
            };
          }
        );
        resources = fediversity.applications.hello.resources fediversity.example-configuration.applications.hello;
        hello-shell = resources.resources.hello.login-shell;
        environment = fediversity.environments.single-nixos-vm.resources.operator-environment.login-shell;
        result = mkDeployment {
          modules = [
            (fediversity.environments.single-nixos-vm.deployment fediversity.example-configuration)
          ];
        };

      in
      {
        number-of-resources = with lib; length (attrNames fediversity.resources);
        inherit (fediversity) example-configuration;
        hello-package-exists = hello-shell.packages ? hello;
        wheel-required = hello-shell.wheel;
        wheel-allowed = environment.wheel;
        operator-shell =
          let
            operator = (environment.apply resources).operator;
          in
          {
            inherit (operator) isNormalUser;
            packages = map (p: "${p.pname}") operator.packages;
            extraGroups = operator.extraGroups;
          };
        deployment = {
          inherit (result) _type;
          deploymentFunction = lib.isFunction result.deploymentFunction;
          getProviders = lib.isFunction result.getProviders;
        };
      };
    expected = {
      number-of-resources = 1;
      example-configuration = {
        enable = true;
        applications.hello.enable = true;
      };
      hello-package-exists = true;
      wheel-required = false;
      wheel-allowed = false;
      operator-shell = {
        isNormalUser = true;
        packages = [ "hello" ];
        extraGroups = [ ];
      };
      deployment = {
        _type = "nixops4Deployment";
        deploymentFunction = true;
        getProviders = true;
      };
    };
  };
}