Class for dealing with Swedish personal identity numbers.

SwedishPersonalIdentityNumber.cs

public class SwedishPersonalIdentityNumber
{
	/// <summary>
	/// Pattern for finding common ways of writing a Swedish personal identity number. It is forgiving and will match the format rather than valid numbers.
	///
	/// Illustrating how it works:
	/// ((19)99)(06)(01)(-)((01)|(TF))(1)(1)
	/// </summary>
	private const string RegexPattern = @"^(?<year>((19)|(20))?(\d\d))(?<month>[01]\d)(?<day>\d\d)(?<flag>[-]|[\+])?(?<county>(\d\d)|(TF))(?<gender>\d)(?<checksum>\d)$";

	public int BirthYear { get; set; }
	public int BirthMonth { get; set; }
	public int BirthDay { get; set; }

	public int CountyCode { get; set; }
	public int GenderCode { get; set; }
	public int Checksum { get; set; }

	public bool IsCoordinationNumber { get; set; }
	public bool IsTemporaryNumber { get; set; }

	public DateTime Birthdate
	{
		get
		{	
			return new DateTime(this.BirthYear, this.BirthMonth, this.BirthDay);
		}

		set
		{
			this.BirthYear = value.Year;
			this.BirthMonth = value.Month;
			this.BirthDay = value.Day;
		}
	}

	public int Age
	{
		get
		{
			var birthdate = this.Birthdate;
			var today = DateTime.Today;
			var result = today.Year - birthdate.Year;

			if (today.Month < birthdate.Month || (today.Month == birthdate.Month && today.Day < birthdate.Day))
			{
				result--;
			}

			return result;
		}
	}

	public SwedishPersonalIdentityNumber()
	{
		this.Birthdate = DateTime.MinValue;
	}

	public SwedishPersonalIdentityNumber(string swedishPersonalIdentityNumber)
		: this()
	{
		var match = Regex.Match(swedishPersonalIdentityNumber.Trim(), RegexPattern);

		if (match.Success == false)
		{
			throw new FormatException("The provided personal identity number is not a valid Swedish personal identity number.");
		}

		this.BirthMonth = Convert.ToInt32(match.Groups["month"].Value);
		this.BirthDay = Convert.ToInt32(match.Groups["day"].Value);

		if (this.BirthDay > 60)
		{
			// For coordination numbers, the day part is added with 60, so we deduct 60.
			this.IsCoordinationNumber = true;
			this.BirthDay = this.BirthDay - 60;
		}

		this.BirthYear = ParseBirthYear(match.Groups["year"].Value, this.BirthMonth, this.BirthDay, match.Groups["flag"] != null ? match.Groups["flag"].Value : null);

		// For temporary numbers, the county part is "TF"
		if (match.Groups["county"].Value == "TF")
		{
			this.IsTemporaryNumber = true;
			this.CountyCode = 0;
		}
		else
		{
			this.CountyCode = Convert.ToInt32(match.Groups["county"].Value);
		}

		this.GenderCode = Convert.ToInt32(match.Groups["gender"].Value);
		this.Checksum = Convert.ToInt32(match.Groups["checksum"].Value);
	}

	private int ParseBirthYear(string birthYear, int month, int day, string flag)
	{
		if (birthYear.Length == 4)
		{
			// String contains full year.
			return Convert.ToInt32(birthYear);
		}
		else
		{
			// String contains partial year.
			var currentDate = DateTime.Today;
			var birthdayThisYear = new DateTime(currentDate.Year, month, day);

			// Convert the two digit year to four digits.
			//

			// Create an object with Swedish culture information.
			var swedishCultureInfo = new CultureInfo("sv-SE");

			// Set the maximum possible year we can convert to. If this years birthday has occurred, last year will be the maximum year.
			swedishCultureInfo.Calendar.TwoDigitYearMax = birthdayThisYear > currentDate ? currentDate.Year - 1 : currentDate.Year;

			if (flag == "+")
			{
				// If the flag is a plus symbol, that means the birthyear is at least 100 years ago. So we can safely remove 100 years from the maximum possible year.
				swedishCultureInfo.Calendar.TwoDigitYearMax -= 100;
			}

			// Calculate the result.
			return swedishCultureInfo.Calendar.ToFourDigitYear(Convert.ToInt32(birthYear));
		}
	}

	#region ToString Methods
	public override string ToString()
	{
		return this.ToString("yymmdd-nnnn");
	}

	public string ToLongString(bool useFlag = true)
	{
		return this.ToString(useFlag ? "yyyymmdd-nnnn" : "yyyymmddnnnn");
	}

	public string ToString(string format)
	{
		var result = format;

		result = result.Replace("yyyy", this.Birthdate.ToString("yyyy"));
		result = result.Replace("yyy", this.Birthdate.ToString("yyy"));
		result = result.Replace("yy", this.Birthdate.ToString("yy"));
		result = result.Replace("mm", this.Birthdate.ToString("MM"));
		result = result.Replace("m", this.Birthdate.ToString("M"));
		result = result.Replace("dd", string.Format("{0:D2}", this.IsCoordinationNumber ? this.BirthDay + 60 : this.BirthDay));
		result = result.Replace("d", string.Format("{0}", this.IsCoordinationNumber ? this.BirthDay + 60 : this.BirthDay));
		result = result.Replace("-", this.Age > 99 ? "+" : "-");
		result = result.Replace("nnnn", string.Format(this.IsTemporaryNumber ? "TF{1}{2}" : "{0:D2}{1}{2}", this.CountyCode, this.GenderCode, this.Checksum));

		return result;
	}
	#endregion

	#region Static Methods
	public static SwedishPersonalIdentityNumber Parse(string s)
	{
		return new SwedishPersonalIdentityNumber(s);
	}

	public static bool Validate(string s)
	{
		var match = Regex.Match(s.Trim(), RegexPattern);

		return match.Success;
	}
	#endregion
}