using System;

using System.Text.RegularExpressions;

public class Program

{

    public static string AnonymiseEmail(string email)

    {

        if (string.IsNullOrEmpty(email) || !email.Contains("@") || !email.Contains(".") || email.Contains(" "))

            return email;

​

        //Récupère la partie avant le @ (sans le @)

        string user = email.Substring(0, email.LastIndexOf("@"));

        if (!string.IsNullOrEmpty(user) && user.Length > 3)

        {

            string patternUser = @"(?<=[\w\.]{2})[\w\.\@]*(?=[\w\.]{1})";

            user = Regex.Replace(user, patternUser, m => new string('*', m.Length));

        }

        Console.WriteLine($"user = {user}");

​

        string domain = ExtractDomain(email);

        if (!string.IsNullOrEmpty(domain) && domain.Length > 5)

        {

            string patternDomain = @"(?<=@[\w\-\._]{2})[\w\-\._]*(?=[\w\-_]{1})";

            domain = Regex.Replace(domain, patternDomain, m => new string('*', m.Length));

        }

        Console.WriteLine($"domain = {domain}");

​

        bool domainHasExtension = email.LastIndexOf(".") > email.LastIndexOf("@");

        string extension = domainHasExtension

            ? email.Substring(email.LastIndexOf(".") + 1, email.Length - email.LastIndexOf(".") - 1)

            : string.Empty;

        Console.WriteLine($"extension = {extension}");

​

        return $"{user}{domain}{extension}";

    }

​

    private static string ExtractDomain(string email)

    {

        int lastArobaseIndex = email.LastIndexOf("@");

        int lengthOfDomainToken = email.LastIndexOf(".") - lastArobaseIndex + 1;

​

        return lengthOfDomainToken >= 0

            ? email.Substring(lastArobaseIndex, lengthOfDomainToken)

            : email.Substring(lastArobaseIndex);

    }

    public static void Main()

    {

        // Cas pourris

        // - Pas de point dans l'extension

        // - Plusieurs "@" ? (possible ou interdit RFC ?)

        // TODO

        // - Tester le nombre de points avant/après "@" ?

        //  => Si aucun point dans le domaine, on renvoie quoi ?

        //var result = AnonymiseEmail("toto.partie_pas_du_tout_anonymisee@domaine_sans_point");

        var result = AnonymiseEmail("plusieurs@arobase@dans@local.part@domaine_sans_point");

        Console.WriteLine("");

        Console.WriteLine($"result = {result}");

    }

}