query.rb

module Analytic

  class Query < OpenStruct
    SPECIAL = {
      'start-index' => 'start_index',
      'max-results' => 'max_results',
      'start_index' => 'start-index',
      'max_results' => 'max-results'
    }

    def to_params
      hash = to_h.delete_if { |k,v| v.nil? }
      hash.deep_transform_keys! do |key|
        SPECIAL.fetch(key.to_s, key.to_s.camelize(:lower))
      end
      hash
    end

    def to_json(*)
      to_h.to_json
    end

    def checksum(digest = Digest::SHA256)
      params = to_params.sort_by { |k, v| k }.map { |row| row.join('=') }
      digest.new.hexdigest(params.join('&'))
    end
  end

end

# irb(main):001:0> q=Analytic::Query.new
#   => #<Analytic::Query>
# irb(main):002:0> q.web_property_id = 1
#   => 1
# irb(main):003:0> q.to_params
#   => {"webPropertyId"=>1}
# irb(main):004:0> q.start_index = 1
#   => 1
# irb(main):005:0> q.to_params
#   => {"webPropertyId"=>1, "start-index"=>1}