require 'date'
class Date
  def nth_weekday(nth,day_of_week)
    nth = nth + 1
    last = nth == 6
    nth = 5 if last
    date = Date.civil(self.year,self.month)
    current_week_day = date.cwday
    day_of_week = 7 if day_of_week == 0
    nth -= 1 if day_of_week >= current_week_day
    offset = (7*nth - (current_week_day - day_of_week))
    new_date = date + (7*nth - (current_week_day - day_of_week))
    return new_date if new_date.month == date.month
    return last ? new_date - 7 : nil
  end
end

puts Date.today.nth_weekday(3,3).strftime('%A %B %d, %Y')
puts Date.today.nth_weekday(4,3).strftime('%A %B %d, %Y')
puts Date.today.nth_weekday(6,3).strftime('%A %B %d, %Y')