正则验证日期

/// <summary>
        /// check date is validate
        /// </summary>
        /// <param name="input"></param>
        /// <returns></returns>
        private bool isValidateDate(string input)
        {
            string pattern = "^(?:19|20)[0-9]{2}[- /](?:(?:(?:0?[13578]|1[02])[- /](?:0?[1-9]|[12][0-9]|3[01]))|(?:(?:0?[2469]|11)[- /](0?[1-9]|[12][0-9]|30)))$";
            if (input.Trim().Length == 0)
            {
                return true;
            }
            if (Regex.IsMatch(input, pattern))
            {
                string[] dates = input.Split(new char[]{'-', '/'});
                int year = int.Parse(dates[0]);
                int month = int.Parse(dates[1]);
                int day = int.Parse(dates[2]);
    
                if (month == 2)
                {
                    if (DateTime.IsLeapYear(year))
                    {
                        if (day >= 30)
                        {
                            return false;
                        }
                    }
                    else 
                    {
                        if (day >= 29)
                        {
                            return false;
                        }
                    }
                }
                return true;
            }
            return false;
        }