class Time

def days_in_month(month, year = now.year)

If no year is specified, it will use the current year.
Return the number of days in the given month. 
def days_in_month(month, year = now.year)
  if month == 2 && ::Date.gregorian_leap?(year)
    29
  else
    COMMON_YEAR_DAYS_IN_MONTH[month]
  end
end