using System;

​

// Normal number

Console.WriteLine("----------------------------------------");

Console.WriteLine("Normal number");

var countrycd = "27";

var areacd = "62";

var teleno = "123 4567";

Console.WriteLine($"Country: {countrycd}, Area: {areacd}, Tel: {teleno}");

Console.WriteLine(ConvertPhoneNumberDataToString(countrycd, areacd, teleno));

// Leading zero in area code

Console.WriteLine("----------------------------------------");

Console.WriteLine("Leading zero in area code");

areacd = "062";

Console.WriteLine($"Country: {countrycd}, Area: {areacd}, Tel: {teleno}");

Console.WriteLine(ConvertPhoneNumberDataToString(countrycd, areacd, teleno));

// Full number in telno as well and leading zero in area code

Console.WriteLine("----------------------------------------");

Console.WriteLine("Full number in telno as well and leading zero in area code");

teleno = "062 034 7657";

Console.WriteLine($"Country: {countrycd}, Area: {areacd}, Tel: {teleno}");

Console.WriteLine(ConvertPhoneNumberDataToString(countrycd, areacd, teleno));

// Full number in telno as well and leading zero in area code

Console.WriteLine("----------------------------------------");

Console.WriteLine("Full number in telno as well and leading zero in area code");

areacd = "62";

Console.WriteLine($"Country: {countrycd}, Area: {areacd}, Tel: {teleno}");

Console.WriteLine(ConvertPhoneNumberDataToString(countrycd, areacd, teleno));

// Missing country code

Console.WriteLine("----------------------------------------");

Console.WriteLine("Missing country code");

countrycd = "";

Console.WriteLine($"Country: {countrycd}, Area: {areacd}, Tel: {teleno}");

Console.WriteLine(ConvertPhoneNumberDataToString(countrycd, areacd, teleno));

// Null country code

Console.WriteLine("----------------------------------------");

Console.WriteLine("Null country code");

countrycd = null;

Console.WriteLine($"Country: {countrycd}, Area: {areacd}, Tel: {teleno}");

Console.WriteLine(ConvertPhoneNumberDataToString(countrycd!, areacd, teleno));

// Missing country code and area code

Console.WriteLine("----------------------------------------");

Console.WriteLine("Missing country code and area code");

countrycd = "";

areacd = "";

Console.WriteLine($"Country: {countrycd}, Area: {areacd}, Tel: {teleno}");

Console.WriteLine(ConvertPhoneNumberDataToString(countrycd, areacd, teleno));

​

​

​

/// <summary>

/// Fix up phone number as much as we can ...

/// If we have a country code, area code needs it's 0 removed, otherwise, leave the 0

/// Also remove the gaps from them all

/// </summary>

string ConvertPhoneNumberDataToString(string countrycd, string areacd, string teleno)

{

    // Return empty if any of the values are empty

    if (string.IsNullOrWhiteSpace(countrycd) ||

        string.IsNullOrWhiteSpace(areacd) ||

        string.IsNullOrWhiteSpace(teleno)

    )

    {

        return string.Empty;

    }

    // Avoid nulls and trim the spaces

    var telcountrycd = countrycd is null

        ?  string.Empty

        :  countrycd.Trim();

    var telareacd = areacd is null

        ?  string.Empty

        :  areacd.Trim();

    var telno = teleno is null

        ?  string.Empty

        :  teleno.Trim().Replace(" ", "");

    // Clean up leading 0s in the area code

    telareacd = telareacd.StartsWith("0")

        ?  telareacd.Substring(1)

        :  telareacd;

​

    // // Return empty if any of the values are empty

    // if (telcountrycd is "" ||

    //     telareacd is "" ||

    //     telno is ""

    // )

    // {

    //     return string.Empty;

    // }

    // Return the number if it's 10 digits

    if (telno.Length is 10)

    {

        return telno;

    }

​

    // Join the three parts together

    var customertelstring = $"{telcountrycd}{telareacd}{telno}";

    // If we have 9 digits, we need to add a 0 to the front

    // Or, if telcountrycd is 27, we need to replace the 27 with a 0

    if (customertelstring.Length is 9)

    {

        customertelstring = telcountrycd is "27"

            ? customertelstring.Replace("27", "0")

            : $"0{customertelstring}";

    }

    // If there is less than 10 digits, return empty

    return customertelstring.Length < 10

        ?  string.Empty

        :  customertelstring;

}

​