rhythm_clock.rb

require 'chronic'

class RhythmClock
  def initialize wake, sleep
    @begin = wake
    @end = sleep
  end

# returns integer in range (0, 100]
  def now(time=DateTime.now)
    elapsed = daysecs(time) - daysecs(@begin)
    awake_period = daysecs(@end) - daysecs(@begin)
    (100 * elapsed / awake_period.to_f).to_i
  end

  private
  def daysecs time
    seconds = 0
    seconds += time.hour * 60 * 60
    seconds += time.min  * 60
    seconds += time.sec
    seconds
  end
end

def main
  wake_up_time = Chronic.parse('6 am')
  sleep_time = Chronic.parse('10 pm')
  rc = RhythmClock.new wake_up_time, sleep_time
  while true
    puts rc.now
    sleep 1
  end
end

main()