using System;

using System.Text;

using System.Collections.Generic;

using System.Linq;

using System.Threading.Tasks;

using System.Linq;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main(){

         var phone = new PhoneNumber("47128696097");

        Console.WriteLine(phone.Number);

    Console.WriteLine(IsValidPhoneNumber(phone.Number));

    Console.WriteLine(GetFormattedPhoneNumber(phone.Number));

    }

        private static bool IsValidPhoneNumber(string phoneNumber)

        {

            var minimumPhoneLength = 5;

            var regexCharsToStrip = new Regex("(?:[^0-9]|(?<=['\"])s)", RegexOptions.CultureInvariant | RegexOptions.Compiled);

            var rawNumber = regexCharsToStrip.Replace(phoneNumber, string.Empty);

​

            return !string.IsNullOrWhiteSpace(phoneNumber)

                && !string.IsNullOrEmpty(rawNumber)

                && rawNumber.Length >= minimumPhoneLength;

        }

        private static string GetFormattedPhoneNumber(string phoneNumber)

        {

            phoneNumber = phoneNumber.Trim();

            var phoneInfo = new PhoneNumber(phoneNumber);

​

            if (string.IsNullOrWhiteSpace(phoneInfo.Number))

            {

                return string.Empty;

            }

​

            var stringBuilder = new StringBuilder();

​

            if (phoneInfo.HasExtension)

            {

                stringBuilder.Append(phoneInfo.Extension + " ");

            }

​

            if (phoneInfo.HasAreaCode)

            {

                stringBuilder.Append(phoneInfo.AreaCode + " ");

            }

​

            var number = phoneInfo.Number.Replace(" ", string.Empty);

​

            if (phoneInfo.HasExtension && number.Length == 9)

            {

                stringBuilder.Append($"{number.Substring(0, 3)} " +

                        $"{number.Substring(3, 3)} {phoneNumber.Substring(6, 3)}");

            }

            else if (phoneInfo.HasAreaCode && number.Length == 8)

            {

                stringBuilder.Append($"{number.Substring(0, 4)} {number.Substring(4, 4)}");

            }

            else if (number[0] == '0' && number.Length == 10)

            {

                stringBuilder.Append($"{number.Substring(0, 2)} " +

                    $"{phoneNumber.Substring(2, 3)} " +

                    $"{phoneNumber.Substring(5, 3)} " +

                    $"{phoneNumber.Substring(8, 3)}");

            }

            else

            {

                stringBuilder.Append(phoneInfo.Number);

            }

​

            return stringBuilder.ToString();

        }

    internal class PhoneNumber

    {

        public PhoneNumber(string phoneNumber)

        {

            Number = phoneNumber;

            Extension = ExtractPhoneExtension(phoneNumber);

            AreaCode = ExtractPhoneAreaCode(phoneNumber);

​

            if (HasExtension)

            {

                Number = Number.Replace(Extension, string.Empty).Trim();

            }

​

            if (HasAreaCode)

            {

                Number = Number.Replace(AreaCode, string.Empty).Trim();

            }

        }

​

        public string Extension { get; }

        public bool HasExtension => !string.IsNullOrEmpty(Extension);

        public string AreaCode { get; }

        public bool HasAreaCode => !string.IsNullOrEmpty(AreaCode);

        public string Number { get; }

​

        private static string ExtractPhoneExtension(string phoneNumber)

        {

            if (phoneNumber == null)

            {

                return null;

            }

​

            if (phoneNumber[0] == '+' && phoneNumber.Length > 3)

            {

                return phoneNumber.Substring(0, 3);

            }

​

            return null;

        }

        private static string ExtractPhoneAreaCode(string phoneNumber)

        {

            if (phoneNumber == null)

            {

                return null;

            }

​

            var regex = new Regex(@"^(\(\d.\))", RegexOptions.CultureInvariant | RegexOptions.Compiled);

            var matches = regex.Match(phoneNumber);

​

            if (matches.Success && matches.Groups.Count >= 1)

            {

                return matches.Groups[0].Value;

            }

​

            return null;

        }

    }

}

​

​