ruby quarter hour range method

time_helper.rb

module TimeHelper
  def quarter_hour_range(timestamp)
    array = timestamp.to_a

    # 1-4th qurater of a hour
    quarter = ((array[1] % 60) / 15.0).ceil - 1
    # 0/15/30/45 start of a quarter
    start_minute = (quarter * 15) % 60
    end_minute = (start_minute + 15) % 60

    array[0] = 0 # set seconds to zero
    array[1] = start_minute
    start_time = Time.zone.local(*array)

    array[1] = end_minute
    end_time = Time.zone.local(*array) - 1.second
    end_time = start_time.end_of_hour if end_minute.zero?

    (start_time..end_time)
  end
end