Paginated mapping to json

helper.rb

def mapping_for_js(resource, options={})
  resource_name = resource.is_a?(ActiveRecord::Relation) ? 
    resource.name.tableize : resource.class.to_s.underscore

  payload = {
    resource_name => JSON.parse(resource.to_json(options[:to_json]))
  }

  # only merge if paginated
  payload.merge!(:paginate => {
    :total_entries => resource.total_entries,
    :prev_page     => resource.previous_page,
    :next_page     => resource.next_page,
    :page          => resource.current_page,
    :total_pages   => resource.total_pages,
    :per_page      => resource.per_page
  }) if (resource.try(:per_page) rescue false)
  # TODO more solid way to ensure this is a paginated object to use with 
  # either via kamamri and will_paginate
  # though 'per_page' is probably a solid sign it does


  payload = payload.to_json if options[:force_to_json]

  unless options[:instance_name].blank?
    var_name = "@#{options[:instance_name]}"

    # if we are setting instance variable, we also want to send that back 
    # as the return
    instance_variable_set var_name, payload
    return instance_variable_get var_name
  end

  payload
end