MailTool/MailFromWho/Format.cs

using System.Text;
using System.Text.RegularExpressions;

namespace MailFromWho
{
    internal class Format
    {
        private readonly Settings _settings;

        public Format(Settings settings)
        {
            _settings = settings;
        }

        internal void CreateCSV()
        {
            string? line;
            Dictionary<string, List<string>> addresses = new Dictionary<string, List<string>>();

            // Read the file and display it line by line.  
            var inFile = new System.IO.StreamReader(_settings.IntermediateFile);
            using (var outFile = new System.IO.StreamWriter(_settings.CsvFile))
            {
                while ((line = inFile.ReadLine()) != null)
                {
                    char[] quotes = { '\"' };
                    var emailAddress = ExtractEmails(line);
                    if (emailAddress != null)
                    {
                        emailAddress = emailAddress.ToLower();
                        var alias = line.Replace($"<{emailAddress}>", "").Trim().Trim(quotes);
                        if (addresses.ContainsKey(emailAddress))
                        {
                            var aliasses = addresses[emailAddress];
                            if (!aliasses.Contains(alias))
                            {
                                aliasses.Add(alias);
                            }
                        }
                        else
                        {
                            var aliasses = new List<string>();
                            if (!string.IsNullOrEmpty(alias))
                            {
                                aliasses.Add(alias);
                            }
                            addresses.Add(emailAddress, aliasses);
                        }
                    }
                }

                List<KeyValuePair<string, List<string>>> addressList = addresses.ToList();

                addressList.Sort(
                    delegate (KeyValuePair<string, List<string>> pair1,
                    KeyValuePair<string, List<string>> pair2)
                    {
                        var emailRegex = new Regex(@"\w+([-+.]\w+)*@(?<domain>\w+([-.]\w+)*\.\w+([-.]\w+)*)",
                            RegexOptions.IgnoreCase);
                        var domain1 = emailRegex.Match(pair1.Key).Groups["domain"].Value;
                        var domain2 = emailRegex.Match(pair2.Key).Groups["domain"].Value;

                        return domain1.CompareTo(domain2);
                    }
                );

                foreach (var address in addressList)
                {
                    var sb = new StringBuilder(address.Key);
                    foreach (var alias in address.Value)
                    {
                        sb.Append(',').Append(alias);
                    }

                    var outLine = sb.ToString();
                    System.Console.WriteLine(outLine);
                    outFile.WriteLine(outLine);
                }
            }

            inFile.Close();
        }

        public string? ExtractEmails(string lineIn)
        {
            var emailRegex = new Regex(@"\w+([-+.]\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*",
                RegexOptions.IgnoreCase);
            //find items that matches with our pattern
            var emailMatches = emailRegex.Matches(lineIn);

            foreach (Match emailMatch in emailMatches)
            {
                return emailMatch.Value;
            }
            return null;
        }
    }
}