{
  lib,
  soonixSubmodule,
  pipelineSubmodule,
  pkgs,
  ...
}: let
  inherit (lib) mkOption types foldr mapAttrsToList concatLists;
in rec {
  configSubmodule = {
    options = {
      soonix = mkOption {
        description = ''
          Configure the soonix `.gitlab-ci.yml` generation.
        '';
        type = types.submodule soonixSubmodule;
        default = {};
      };
      nixJobsByDefault = mkOption {
        description = ''
          Whether to transform all jobs to nix-configured jobs by default.
          If false, you need to set [`nix.enable`](#pipelinesnamejobsnamenixenable)
          for each job you want to be transformed.
        '';
        type = types.bool;
        default = true;
      };
    };
  };

  nixCiSubmodule = {config, ...}: {
    imports = [(pkgs.path + /nixos/modules/misc/assertions.nix)];
    options = {
      config = mkOption {
        description = ''
          Configuration of Nix-GitLab-CI itself.
        '';
        type = types.submodule configSubmodule;
        default = {};
      };
      pipelines = mkOption {
        description = ''
          Defines all pipelines.
        '';
        type = types.attrsOf (types.submoduleWith {
          modules = [pipelineSubmodule];
          specialArgs.rootConfig = config.config;
        });
        default = {};
      };

      packages = mkOption {
        description = ''
          Final packages for use in CI. (readonly)
        '';
        readOnly = true;
        type = types.attrsOf types.package;
      };
      soonix = mkOption {
        description = ''
          Soonix config for generating `.gitlab-ci.yml`. (readonly)

          See [`config.soonix`](#configsoonix) for configuring this.
        '';
        readOnly = true;
        type = types.attrs;
      };
    };
    config = {
      # Propagate pipeline assertions to the root level
      assertions = concatLists (
        mapAttrsToList (_name: pipeline: pipeline.assertions) config.pipelines
      );
      packages = foldr (pipeline: acc: acc // pipeline) {} (
        map (pipeline: pipeline.packages) (builtins.attrValues config.pipelines)
      );
      soonix = config.config.soonix.finalConfig;
    };
  };
}