using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        var phone1 = "9012345678x123";

        var phone2 = "9012345678";

        Console.WriteLine("Phone Link: {0}", FormatPhoneLink(phone1));

        Console.WriteLine("Phone Display: {0}", FormatPhoneDisplay(phone1));

        Console.WriteLine();

        Console.WriteLine();

        Console.WriteLine("Phone Link: {0}", FormatPhoneLink(phone2));

        Console.WriteLine("Phone Display: {0}", FormatPhoneDisplay(phone2));

    }

    private static string FormatPhoneLink(string value)

    {

        var phoneWithExtensionPattern = @"^(\d{3})(\d{3})(\d{4})x(\d{1,5})$";

        var phoneWithoutExtensionPattern = @"^(\d{3})(\d{3})(\d{4})$";

        if (Regex.IsMatch(value, phoneWithExtensionPattern))

        {

            return Regex.Replace(value, phoneWithExtensionPattern, "tel:+1-$1-$2-$3;ext=$4");

        }

        else if (Regex.IsMatch(value, phoneWithoutExtensionPattern))

        {

            return Regex.Replace(value, phoneWithoutExtensionPattern, "tel:+1-$1-$2-$3");

        }

        return value;

    }

    private static string FormatPhoneDisplay(string value)

    {

        var phoneWithExtensionPattern = @"^(\d{3})(\d{3})(\d{4})x(\d{1,5})$";

        var phoneWithoutExtensionPattern = @"^(\d{3})(\d{3})(\d{4})$";

        if (Regex.IsMatch(value, phoneWithExtensionPattern))

        {

            return Regex.Replace(value, phoneWithExtensionPattern, "($1) $2-$3 x $4");

        }

        else if (Regex.IsMatch(value, phoneWithoutExtensionPattern))

        {

            return Regex.Replace(value, phoneWithoutExtensionPattern, "($1) $2-$3");

        }

        return value;

    }

}