#!/usr/local/bin/ruby
class Date
   attr_reader :year, :month, :day
   
   def initialize(y, m, d)
      if check_date(y, m, d)
         @year, @month, @day = y, m, d
      else
         @year, @month, @day = 2000, 1, 1
      end
   end

   @@mon = [nil,"Jan","Feb","Mar","Apr",
            "May","Jun","Jul","Aug",
            "Sep","Oct","Nov","Dec"]
   @@days = [0, 31, 28, 31, 30, 31, 30,
                31, 31, 30, 31, 30, 31]
   def check_date(y, m, d)
      if m < 1 or m > 12 or 
            d < 0 or d > 31 or y < 0
         false
      elsif d > 0 and d <= @@days[m]
         true
      elsif m == 2 and d == 29 and
           is_leap(y)
         true
      else
         false
      end
   end
   
   def is_leap(y)
      if (y%400 == 0 or
            (y%4 == 0 and y%100 != 0) )
         true
      else
         false
      end
   end
      
   def to_s
      @@mon[@month] + " " + day.to_s +
         ", " + year.to_s
   end
   
   def incr_day
      @day +=1
      if not (@month == 2 and 
              is_leap(@year) and
              @day == 29) and
            @day > @@days[@month]
         @day = 1
         incr_month
      end
   end

   def incr_month
      @month +=1
      if @month > 12
         @month = 1
         incr_year
      end
   end
   
   def incr_year
      @year += 1
   end

end

def test_date(y, m, d)
   date = Date.new(y, m, d)
   print "Start Date:  ",date," "
   date.incr_day
   print "\n   Next day: ", date
   date.incr_day
   print "\n   Next day: ", date
   date.incr_day
   print "\n   Next day: ", date,
      "\n"
end
test_date(2004, 4, 22)
test_date(2000, 2, 28)
test_date(2001, 2, 27)
test_date(2001, 12, 30)