{ config, lib, ... }:
let
  metadataType =
    with lib;
    submodule {
      options = {
        description = {
          type = with types; nullOr str;
          default = null;
        };
        # other metadata (look it up)
      };
    };
  inner = with lib; {
    # source: https://wiki.nixos.org/wiki/Flakes#Output_schema
    checks = mkOption {
      # NOTE: this is different from the flakes themselves -- this version accepts
      # anything (not just a derivation):
      # - for a derivation type, the behavior is the same
      # - for a non-derivation type, expression gets deep-evaluated instead
      type = with types; attrsOf types.raw;
      description = "Evaluated by `nix flake check`";
      default = { };
    };
    packages = mkOption {
      type = with types; attrsOf package;
      description = "Executed by `nix build .#<name>`";
      default = { };
    };
    apps = mkOption {
      description = "Executed by `nix run .#<name>`";
      type =
        with types;
        attrsOf (submodule {
          options = {
            program = mkOption1 {
              description = "An executable to run";
              type = pathInStore;
            };
            meta = mkOption {
              description = "The executable metadata";
              type = metadataType;
              default = { };
            };
          };
        });
      default = { };
    };
  };
  # decorates the inner options with additinal "forSystem" option used to specialize on the
  # system
  forSystem =
    with lib;
    inner:
    inner
    // {
      forSystem = mkOption {
        description = "flake outputs only present at a specific system";
        type = attrsOf (submodule {
          options = inner;
        });
      };
    };
  # decorates the inner options with additinal "raw" option used to expose other unchecked
  # flake outputs verbatim
  raw =
    with lib;
    inner:
    inner
    // {
      raw = mkOption {
        description = "flake outputs only present at a specific system";
        type = attrsOf (submodule {
          options = inner;
        });
      };
    };
in
{
  # options = (passthru (forSystem (passthru inner)));
  options = inner // {
    __check = {
      type = lib.types.listOf lib.types.raw;
      default =
        (builtins.attrValues config.check)
        // (builtins.attrValues config.packages)
        // (builtins.attrValues config.apps);
    };
  };
}