module JSONAPI::Resources::FiltersDsl

def filters(*filter_names)
  @filters ||= []
  @filters.concat(filter_names.map(&:to_sym))
  @filters.uniq!
end

def permitted_filters
  declared_filters = instance_variable_defined?(:@filters)
  filter_list = @filters || []
  if !declared_filters &&
     superclass != JSONAPI::Resource &&
     superclass.respond_to?(:permitted_filters)
    filter_list = superclass.permitted_filters + filter_list
  end
  filter_list.uniq
end

def permitted_filters_through
  relationship_names
end