{ lib, config, pkgs, inputs, ... }:

with lib;
with lib.plusultra;
let
  cfg = config.plusultra.services.vault-agent;

  # nixos-vault-service places generated files here:
  # https://github.com/DeterminateSystems/nixos-vault-service/blob/45e65627dff5dc4bb40d0f2595916f37e78959c1/module/helpers.nix#L4
  secret-files-root = "/tmp/detsys-vault";
  environment-files-root = "/run/keys/environment";

  create-environment-files-submodule = service-name: types.submodule ({ name, ... }: {
    options = {
      text = mkOpt (types.nullOr types.str) null "An inline template for Vault to template.";
      source = mkOpt (types.nullOr types.path) null "The file with environment variables for Vault to template.";
      path = mkOption {
        readOnly = true;
        type = types.str;
        description = "The path to the environment file.";
        default = "${environment-files-root}/${service-name}/${name}.EnvFile";
        defaultText = "${environment-files-root}/<service-name>/<template-name>.EnvFile";
      };
    };
  });

  secret-files-submodule = types.submodule ({ name, ... }: {
    options = {
      text = mkOpt (types.nullOr types.str) null "An inline template for Vault to template.";
      source = mkOpt (types.nullOr types.path) null "The file for Vault to template.";
      permissions = mkOpt types.str "0400" "The octal mode of this file.";
      change-action = mkOpt (types.nullOr (types.enum [ "restart" "stop" "none" ])) null "The action to take when secrets change.";
      path = mkOption {
        readOnly = true;
        type = types.str;
        description = "The path to the secret file.";
        default = "${secret-files-root}/${name}";
      };
    };
  });


  services-submodule =
    types.submodule
      ({ name, config, ... }: {
        options = {
          enable = mkBoolOpt true "Whether to enable Vault Agent for this service.";
          settings = mkOpt types.attrs { } "Vault Agent configuration.";
          secrets = {
            environment = {
              force = mkOpt types.bool false "Whether or not to force the use of Vault Agent's environment files.";
              change-action = mkOpt (types.enum [ "restart" "stop" "none" ]) "restart" "The action to take when secrets change.";
              templates = mkOpt (types.attrsOf (create-environment-files-submodule name)) { } "Environment variable files for Vault to template.";
              template = mkOpt (types.nullOr (types.either types.path types.str)) null "An environment variable template.";
              paths = mkOption {
                readOnly = true;
                type = types.listOf types.str;
                description = "Paths to all of the environment files";
                default =
                  if config.secrets.environment.template != null then
                    [ "${environment-files-root}/${name}/EnvFile" ]
                  else
                    (
                      mapAttrsToList
                        (template-name: value: value.path)
                        config.secrets.environment.templates
                    );
              };
            };

            file = {
              change-action = mkOpt (types.enum [ "restart" "stop" "none" ]) "restart" "The action to take when secrets change.";
              files = mkOption {
                description = "Secret files to template.";
                default = { };
                type = types.attrsOf secret-files-submodule;
              };
            };
          };
        };
      });
in
{
  # imports = [
  #   inputs.vault-service.nixosModules.nixos-vault-service
  # ];

  options.plusultra.services.vault-agent = {
    enable = mkEnableOption "Vault Agent";

    settings = mkOpt types.attrs { } "Default Vault Agent configuration.";

    services = mkOption {
      description = "Services to install Vault Agent into.";
      default = { };
      type = types.attrsOf services-submodule;
    };
  };

  config = mkIf cfg.enable {
    assertions = flatten (mapAttrsToList
      (service-name: service:
        (mapAttrsToList
          (template-name: template:
            {
              assertion = (template.source != null && template.text == null) || (template.source == null && template.text != null);
              message = "plusultra.services.vault-agent.services.${service-name}.secrets.environment.templates.${template-name} must set either `source` or `text`.";
            }
          )
          service.secrets.environment.templates)
        ++
        (mapAttrsToList
          (file-name: file:
            {
              assertion = (file.source != null && file.text == null) || (file.source == null && file.text != null);
              message = "plusultra.services.vault-agent.services.${service-name}.secrets.file.files.${file-name} must set either `source` or `text`.";
            }
          )
          service.secrets.file.files)
      )
      cfg.services);

    systemd.services = mapAttrs
      (service-name: value: mkIf value.secrets.environment.force {
        serviceConfig.EnvironmentFile = mkForce value.secrets.environment.paths;
      })
      cfg.services;

    detsys.vaultAgent = {
      defaultAgentConfig = cfg.settings;

      systemd.services = mapAttrs
        (service-name: value: {
          inherit (value) enable;

          agentConfig = value.settings;

          environment = {
            changeAction = value.secrets.environment.change-action;

            templateFiles = mapAttrs
              (template-name: value: {
                file =
                  if value.source != null then
                    value.source
                  else
                    pkgs.writeText "${service-name}-${template-name}-env-template" value.text;
              })
              value.secrets.environment.templates;

            template =
              if (builtins.isPath value.secrets.environment.template) || (builtins.isNull value.secrets.environment.template) then
                value.secrets.environment.template
              else
                pkgs.writeText "${service-name}-env-template" value.secrets.environment.template;
          };

          secretFiles = {
            defaultChangeAction = value.secrets.file.change-action;

            files = mapAttrs
              (file-name: value: {
                changeAction = value.change-action;
                template = value.text;
                templateFile = value.source;
                perms = value.permissions;
              })
              value.secrets.file.files;
          };
        })
        cfg.services;
    };
  };
}