common/PendingEmails/AppSettings.cs

namespace PendingEmails
{
    using System.Collections.Generic;
    using System.Configuration;
    using System.IO;
    using System.Linq;

    public static partial class Program
    {
        public class AppSettings
        {
            public static string LogFolder { get; private set; }

            public static string MSSQLConnectionString { get; private set; }

            public static string Sender { get; private set; }

            public static string ExcludeRecipients { get; private set; }

            public static string SMTPHost { get; private set; }

            public static int SMTPPort { get; private set; }

            public static string SMTPUsername { get; private set; }

            public static string SMTPPassword { get; private set; }

            public static int Interval { get; private set; }

            public static bool TryLoadExeConfiguration(out ICollection<string> errors)
            {
                errors = new HashSet<string>();

                var exeFileInfo = new FileInfo(typeof(Program).Assembly.Location);
                var settings = ConfigurationManager
                    .OpenExeConfiguration(exeFileInfo.FullName)
                    ?.AppSettings
                    ?.Settings;
                var loaded = true;

                if (settings is null)
                {
                    errors.Add($"{exeFileInfo.Name} nicht gefunden.");

                    loaded = false;
                }
                else
                {
                    var keys = settings.AllKeys;

                    LogFolder = exeFileInfo.Directory.FullName;

                    if (!keys.Any(x => x == nameof(LogFolder)))
                    {
                        errors.Add($"{nameof(LogFolder)} nicht definiert in die {exeFileInfo.Name}.");
                        errors.Add($"{LogFolder} wird benutzt.");
                    }
                    else
                    {
                        LogFolder = settings[nameof(LogFolder)]?.Value;
                    }

                    if (!keys.Any(x => x == nameof(MSSQLConnectionString)))
                    {
                        errors.Add($"{nameof(MSSQLConnectionString)} nicht definiert in die {exeFileInfo.Name}.");

                        loaded = false;
                    }
                    else
                    {
                        MSSQLConnectionString = settings[nameof(MSSQLConnectionString)]?.Value;
                    }

                    if (!keys.Any(x => x == nameof(Sender)))
                    {
                        errors.Add($"{nameof(Sender)} nicht definiert in die {exeFileInfo.Name}.");

                        loaded = false;
                    }
                    else
                    {
                        Sender = settings[nameof(Sender)]?.Value;
                    }

                    if (!keys.Any(x => x == nameof(ExcludeRecipients)))
                    {
                        errors.Add($"{nameof(ExcludeRecipients)} nicht definiert in die {exeFileInfo.Name}.");
                    }
                    else
                    {
                        ExcludeRecipients = settings[nameof(ExcludeRecipients)]?.Value;
                    }

                    if (!keys.Any(x => x == nameof(SMTPHost)))
                    {
                        errors.Add($"{nameof(SMTPHost)} nicht definiert in die {exeFileInfo.Name}.");

                        loaded = false;
                    }
                    else
                    {
                        SMTPHost = settings[nameof(SMTPHost)]?.Value;
                    }

                    if (!keys.Any(x => x == nameof(SMTPPort)))
                    {
                        errors.Add($"{nameof(SMTPPort)} nicht definiert in die {exeFileInfo.Name}.");

                        loaded = false;
                    }
                    else if (!int.TryParse($"{settings[nameof(SMTPPort)]?.Value}", out var smtpPort))
                    {
                        errors.Add($"{nameof(SMTPPort)} ist ungültig.");

                        loaded = false;
                    }
                    else
                    {
                        SMTPPort = smtpPort;
                    }

                    if (!keys.Any(x => x == nameof(SMTPUsername)))
                    {
                        errors.Add($"{nameof(SMTPUsername)} nicht definiert in die {exeFileInfo.Name}.");
                    }
                    else
                    {
                        SMTPUsername = settings[nameof(SMTPUsername)]?.Value;
                    }

                    if (!keys.Any(x => x == nameof(SMTPPassword)))
                    {
                        errors.Add($"{nameof(SMTPPassword)} nicht definiert in die {exeFileInfo.Name}.");
                    }
                    else
                    {
                        SMTPPassword = settings[nameof(SMTPPassword)]?.Value;
                    }

                    Interval = 600_000;

                    if (!keys.Any(x => x == nameof(Interval)))
                    {
                        errors.Add($"{nameof(Interval)} nicht definiert in die {exeFileInfo.Name}.");
                    }
                    else if (!int.TryParse($"{settings[nameof(Interval)]?.Value}", out var interval))
                    {
                        errors.Add($"{nameof(Interval)} ist ungültig.");
                    }
                    else
                    {
                        Interval = interval;
                    }
                }

                return loaded;
            }
        }
    }
}