class SourceSet {

    public Set<String> getResources(Difficulty difficulty) {
        if (difficulties.has(difficulty.toString())) {
            Type setType = new TypeToken<Set<String>>() {
            }.getType();
            JsonElement element = difficulties.get(difficulty.toString());
            return new Gson().fromJson(element, setType);
        } else {
            return Collections.emptySet();
        }
    }

    public  SourceSet(String resourceFile);

}