Gfrktyl

I have a small C# program that validates Swedish social security numbers 'Personnummer', https://en.wikipedia.org/wiki/Personal_identity_number_(Sweden)

I chose to use Regex as there are many different ways it can be input

using System;

using System.Globalization;

using System.Linq;

using System.Text.RegularExpressions;



namespace Personnummer

{

    /// <summary>

    /// Class used to verify Swedish social security numbers.

    /// </summary>

    public static class Personnummer

    {

        private static readonly Regex regex;

        private static readonly CultureInfo cultureInfo;



        static Personnummer()

        {

            cultureInfo = new CultureInfo("sv-SE");

            regex       = new Regex(@"(d{2}){0,1}(d{2})(d{2})(d{2})([-|+]{0,1})?(d{3})(d{0,1})");

        }



        /// <summary>

        /// Calculates the checksum value of a given digit-sequence as string by using the luhn/mod10 algorithm.

        /// </summary>

        /// <param name="value">Sequense of digits as a string.</param>

        /// <returns>Resulting checksum value.</returns>

        private static int Luhn(string value)

        {

            // Luhm algorithm doubles every other number in the value.

            // To get the correct checksum digit we aught to append a 0 on the sequence.

            // If the result becomes a two digit number, subtract 9 from the value.

            // If the total sum is not a 0, the last checksum value should be subtracted from 10.

            // The resulting value is the check value that we use as control number.



            // The value passed is a string, so we aught to get the actual integer value from each char (i.e., subtract '0' which is 48).

            int t = value.ToCharArray().Select(d => d - 48).ToArray();

            int sum = 0;

            int temp;

            for (int i = t.Length; i -->0; )

            {

                temp = t[i];

                sum += (i % 2 == t.Length % 2) 

                    ? ((temp * 2) % 10) + temp / 5 

                    : temp;

            }



            return sum % 10;

        }



        /// <summary>

        /// Function to make sure that the passed year, month and day is parseable to a date.

        /// </summary>

        /// <param name="year">Years as string.</param>

        /// <param name="month">Month as int.</param>

        /// <param name="day">Day as int.</param>

        /// <returns>Result.</returns>

        private static bool TestDate(string year, int month, int day)

        {

            try

            {

                DateTime dt = new DateTime(cultureInfo.Calendar.ToFourDigitYear(int.Parse(year)), month, day);

                return true;

            }

            catch

            {

                return false;

            }

        }



        /// <summary>

        /// Validate Swedish social security number.

        /// </summary>

        /// <param name="value">Value as string.</param>

        /// <returns>Result.</returns>

        public static bool Valid(string value)

        {

            MatchCollection matches = regex.Matches(value);



            if (matches.Count < 1 || matches[0].Groups.Count < 7)

            {

                return false;

            }



            GroupCollection groups = matches[0].Groups;

            int month, day, check;

            string yStr;

            try

            {

                yStr  = (groups[2].Value.Length == 4) ? groups[2].Value.Substring(2) : groups[2].Value;

                month = int.Parse(groups[3].Value);

                day   = int.Parse(groups[4].Value);

                check = int.Parse(groups[7].Value);

            }

            catch

            {

                // Could not parse. So invalid.

                return false;

            }



            bool valid = Luhn($"{yStr}{groups[3].Value}{groups[4].Value}{groups[6].Value}{check}") == 0;

            return valid && (TestDate(yStr, month, day) || TestDate(yStr, month, day - 60));

        }



        /// <summary>

        /// Validate Swedish social security number.

        /// </summary>

        /// <param name="value">Value as long.</param>

        /// <returns>Result.</returns>

        public static bool Valid(long value)

        {

            return Valid(value.ToString());

        }



    }

}