{
  lib,
  config,
  helpers,
  ...
}:
with lib; rec {
  mkExtension = {
    name,
    defaultPackage,
    extensionName ? name,
    settingsOptions ? {},
    settingsExample ? null,
    extraOptions ? {},
    imports ? [],
    optionsRenamedToSettings ? [],
    extraConfig ? cfg: {},
  }: {
    # TODO remove this once all deprecation warnings will have been removed.
    imports = let
      basePluginPath = ["plugins" "telescope" "extensions" name];
      settingsPath = basePluginPath ++ ["settings"];
    in
      imports
      ++ (
        map
        (
          option: let
            optionPath =
              if isString option
              then [option]
              else option; # option is already a path (i.e. a list)

            optionPathSnakeCase = map helpers.toSnakeCase optionPath;
          in
            mkRenamedOptionModule
            (basePluginPath ++ optionPath)
            (settingsPath ++ optionPathSnakeCase)
        )
        optionsRenamedToSettings
      );

    options.plugins.telescope.extensions.${name} =
      {
        enable = mkEnableOption "the `${name}` telescope extension";

        package = helpers.mkPackageOption name defaultPackage;

        settings = helpers.mkSettingsOption {
          description = "settings for the `${name}` telescope extension.";
          options = settingsOptions;
          example = settingsExample;
        };
      }
      // extraOptions;

    config = let
      cfg = config.plugins.telescope.extensions.${name};
    in
      mkIf cfg.enable
      (
        mkMerge [
          {
            extraPlugins = [cfg.package];

            plugins.telescope = {
              enabledExtensions = [extensionName];
              settings.extensions.${extensionName} = cfg.settings;
            };
          }
          (extraConfig cfg)
        ]
      );
  };

  mkModeMappingsOption = mode: defaults:
    mkOption {
      type = with helpers.nixvimTypes; attrsOf strLuaFn;
      default = {};
      description = ''
        Keymaps in ${mode} mode.

        Default:
        ```nix
          ${defaults}
        ```
      '';
      apply = mapAttrs (_: helpers.mkRaw);
    };

  mkMappingsOption = {
    insertDefaults,
    normalDefaults,
  }: {
    i = mkModeMappingsOption "insert" insertDefaults;
    n = mkModeMappingsOption "normal" normalDefaults;
  };
}