{
  config,
  lib,
  ...
}:
with lib;
let
  cfg = config.modules.shell;
  zshCfg = config.modules.zsh;
in
{
  options.modules.shell = {
    defaultShell = mkOption {
      type = types.enum [
        "bash"
        "zsh"
      ];
      default = "zsh";
      description = ''
        The default shell to use for your user account.
      '';
    };
  };

  config.assertions = []
    ++ (if cfg.defaultShell == "zsh"
          then [{
            assertion = zshCfg.enable;
            message = "You have selected zsh as the default shell, but you haven't enabled it in your configuration.\n\nPlease enable it by adding `modules.zsh.enable = true`.";
          }]
        else []);
}