{
  lib,
  soonixSubmodule,
  pipelineSubmodule,
  ...
}: let
  inherit (lib) mkOption types foldr;
in rec {
  autoChecksSubmodule = {
    options = {
      enable = mkOption {
        description = ''
          Auto-generate CI jobs from [`checks`](#checks).

          Each check becomes a job that runs `nix build .#checks.<system>.<name>`.
        '';
        type = types.bool;
        default = false;
      };
      stage = mkOption {
        description = ''
          Stage to assign to auto-generated check jobs.
        '';
        type = types.str;
        default = "test";
      };
      tags = mkOption {
        description = ''
          Tags to assign to auto-generated check jobs.
        '';
        type = types.listOf types.str;
        default = [];
      };
      pipeline = mkOption {
        description = ''
          Name of the pipeline to add auto-generated check jobs to.
        '';
        type = types.str;
        default = "default";
      };
    };
  };

  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;
      };
      autoChecks = mkOption {
        description = ''
          Auto-generate CI jobs from flake checks.

          See [`config.autoChecks`](#configautochecks) for configuration options.
        '';
        type = types.submodule autoChecksSubmodule;
        default = {};
      };
    };
  };

  nixCiSubmodule = {config, ...}: let
    system = config.system;
  in {
    options = {
      system = mkOption {
        description = ''
          System identifier (e.g. `"x86_64-linux"`).
          Used when building checks with `nix build .#checks.<system>.<name>`.
          Set automatically by `flakeModule` or `cilib.mkCI`.
        '';
        type = types.str;
      };
      checks = mkOption {
        description = ''
          Nix flake checks to optionally auto-generate CI jobs from.

          Each attribute must be a derivation. The attribute name becomes the CI job name.
          Requires [`config.autoChecks.enable`](#configautochecksenable) to take effect.
        '';
        type = types.attrsOf types.package;
        default = {};
      };
      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;
            rootChecks = config.checks;
            rootAutoChecks = config.config.autoChecks;
            inherit system;
          };
        });
        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 = {
      packages = foldr (pipeline: acc: acc // pipeline) {} (
        map (pipeline: pipeline.packages) (builtins.attrValues config.pipelines)
      );
      soonix = config.config.soonix.finalConfig;
    };
  };
}