kaminari + JSON API pagination helper

paginate.rb

def paginate(scope, default_per_page = 20)
  collection = scope.page(params[:page]).per((params[:per_page] || default_per_page).to_i)

  current, total, per_page = collection.current_page, collection.total_pages, collection.limit_value

  render json: [{
    pagination: {
      current:  current,
      previous: (current > 1 ? (current - 1) : nil),
      next:     (current == total ? nil : (current + 1)),
      per_page: per_page,
      pages:    total,
      count:    collection.total_count
    }
  }, collection]
end