nixos-config/modules/themes/default.nix

{ config, options, lib, pkgs, ... }:

with lib;

let
  cfg = config.modules.themes;
  my = import ../../lib {
    inherit pkgs;
    lib = lib;
  };
in {
  assertions = [{
    assertion = my.countAttrs (_: x: x.enable) cfg < 2;
    message = "Can't have more than one theme enabled at a time";
  }];

  imports = [ ./fair-and-square ];
}