accommodation.rb

def pending_total
  if not_needed?
    0.00
  else
    # everyone gets the member pricing
    daily_rate = ACCOMMODATION_RATES[room_type][:member]
    departure_date = departure.to_date
    arrival_date = arrival.to_date
    total_days = departure_date - arrival_date
    before_discounted_days = [[start_date - arrival_date, 3].min, 0].max
    after_discounted_days = [[departure_date - end_date, 3].min, 0].max
    discounted_days = before_discounted_days + after_discounted_days
    (discounted_days * DISCOUNT_RATE) + ((total_days - discounted_days) * daily_rate)
  end
end

registration.rb

  def accommodation_total
    accommodation ? accommodation.total + discounted_stay_price : 0.0
  end

  def discounted_stay_price
    discounted_additional_days * DISCOUNTED_STAY_RATE
  end

  def customer_stay_duration
    (departure - arrival).to_i
  end

  def discounted_additional_days
    additional_days > MAX_DISCOUNTED_DAYS ? MAX_DISCOUNTED_DAYS : additional_days
  end

  def additional_days
    (location_duration - customer_stay_duration).to_i
  end

  def location_duration
    (location.end_date - location.start_date).to_i
  end