module Aging

# File lib/aging.rb, line 7
def count_year
  # alias self
  from_date = self
  klass = self.class
  to_date = klass.today
  # TODO: error
  raise if to_date < from_date

  birthday_in_this_year = klass.new(
    to_date.year,
    from_date.month,
    from_date.day
  )

  if to_date < birthday_in_this_year
    # before
    to_date.year - from_date.year - 1
  else
    # after
    to_date.year - from_date.year
  end
end