//
//  Class:			BSMDPopClient
//	Current CLR:	4.0.30319.34209
//	System:			Microsoft Visual Studio 10.0
//	Author:			dani
// 	Created:		6/15/2015 8:43:41 PM
//
//	Copyright (c) 2015 Informatikbüro Daniel Schick. All rights reserved.

using System;
using System.IO;
using log4net;
using System.Security.Cryptography.X509Certificates;
using System.Net.Security;

using MimeKit;
using MailKit.Security;
using MailKit.Net.Pop3;
using MailKit.Net.Smtp;

using EmailValidation;

namespace bsmd.email
{
    public class BSMDPopClient : IDisposable
    {

        #region Fields

        private readonly Pop3Client pop3Client;
        private readonly ILog _log = LogManager.GetLogger(typeof(BSMDPopClient));
        private int currentMail = 0;

        #endregion

        #region Construction / Destruction

        public BSMDPopClient()
        {
            try
            {
                this.pop3Client = new Pop3Client(new MailKitLogger());
                this.pop3Client.ServerCertificateValidationCallback = ValidateServerCertificate;
                bool  useSSL = true;                                
                this.pop3Client.Connect(Properties.Settings.Default.POP3Server, Properties.Settings.Default.POP3Port, useSSL);                
                this.pop3Client.Authenticate(Properties.Settings.Default.POP3User, Properties.Settings.Default.POP3Password);
                this.IsConnected = true;
            }
            catch (Exception ex)
            {
                _log.ErrorFormat("Error connecting to POP3 Server {0}: {1}", Properties.Settings.Default.POP3Server, ex.Message);
                _log.DebugFormat("User:{0} Pw:{1}", Properties.Settings.Default.POP3User, Properties.Settings.Default.POP3Password);
            }
        }

        public void Dispose()
        {
            if (this.pop3Client != null)
            {
                if (this.pop3Client.IsConnected)
                    this.pop3Client.Disconnect(true);
                this.pop3Client.Dispose();
            }
        }

        #endregion

        #region Hack

        /// <summary>
        /// Diese Funktion validiert *jedes* Zertifikat und ist eigentlich scheiße. Das geht nur so im abgeschlossenen BSMD Netz!
        /// </summary>        
        public static bool ValidateServerCertificate(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
        {
            return true;
        }

        #endregion

        #region Properties

        public bool IsConnected { get; } = false;

        #endregion

        #region E-Mail receive helper / convenience funcs

        public bool ReceiveSingleMailText(out string messageId, out string sender, out string subject, out string body)
        {
            messageId = null;
            sender = null;
            subject = null;
            body = null;

            if (!IsConnected) return false;
            int messageCount = this.pop3Client.GetMessageCount();

            if (messageCount > this.currentMail)
            {
                MimeMessage mailMessage = this.pop3Client.GetMessage(this.currentMail);
                if((mailMessage.Sender != null) && EmailValidator.Validate(mailMessage.Sender.Address))
                    sender = mailMessage.Sender.Address;
                if ((sender == null) && mailMessage.From.Count > 0)
                {
                    foreach (MailboxAddress ma in mailMessage.From.Mailboxes)
                    {
                        if(EmailValidator.Validate(ma.Address))
                        {
                            sender = ma.Address;
                            break;
                        }                        
                    }
                }

                body = mailMessage.TextBody;
                messageId = mailMessage.MessageId;
                subject = mailMessage.Subject;
                this.currentMail++; // advance message pointer

                return true;
            }
            else
            {
                return false;
            }
        }

        public bool ReceiveSingleMail(out string attachmentLocalFile, out string messageId, out string sender, out string subject)
        {
            attachmentLocalFile = null;
            messageId = null;
            sender = null;
            subject = null;

            if (!IsConnected) return false;

            int messageCount = this.pop3Client.GetMessageCount();
            if (messageCount > this.currentMail)
            {
                MimeMessage mailMessage = this.pop3Client.GetMessage(this.currentMail);

                if((mailMessage.Sender != null) && EmailValidator.Validate(mailMessage.Sender.Address))               
                    sender = mailMessage.Sender.Address;
                if ((sender == null) && (mailMessage.From.Count > 0))
                {
                    foreach (MailboxAddress ma in mailMessage.From.Mailboxes)
                    {
                        if (EmailValidator.Validate(ma.Address))
                        {
                            sender = ma.Address;
                            break;
                        }
                    }
                }                    

                messageId = mailMessage.MessageId;
                subject = mailMessage.Subject;
                
                foreach (MimeEntity attachment in mailMessage.Attachments)
                {
                    if (attachment is MessagePart rfc822)
                    {
                        string filename = attachment.ContentDisposition?.FileName;
                        if(filename == null)
                        {
                            _log.InfoFormat("attachment {0} has no filename", attachment.ContentId);
                            continue;
                        }
                        _log.InfoFormat("found attachment named {0}, ContentType {1}", filename, attachment.ContentType);                        

                        if (filename.EndsWith(".xls", StringComparison.InvariantCultureIgnoreCase) ||
                            filename.EndsWith(".xlsx", StringComparison.InvariantCultureIgnoreCase))
                        {
                            attachmentLocalFile = Path.Combine(Properties.Settings.Default.ArchiveFolder, filename);
                            using (var stream = File.Create(attachmentLocalFile))
                                rfc822.Message.WriteTo(stream);
                        }                        
                    } 
                    else
                    {
                        var part = (MimePart)attachment;
                        var filename = part.FileName;
                        if (filename != null)
                        {
                            if (filename.EndsWith(".xls", StringComparison.InvariantCultureIgnoreCase) ||
                            filename.EndsWith(".xlsx", StringComparison.InvariantCultureIgnoreCase))
                            {
                                attachmentLocalFile = Path.Combine(Properties.Settings.Default.ArchiveFolder, filename);
                                using (var stream = File.Create(attachmentLocalFile))
                                    part.Content.DecodeTo(stream);
                            }
                        }
                    }
                }                

                this.currentMail++; // advance message pointer

                return true;
            }
            else
            {
                _log.Info("no new mail on server");
                return false;
            }            
        }

        public string GetNameOfFirstMailEmailPDFAttachment(string messageId)
        {
            if (IsConnected)
            {
                int messageCount = this.pop3Client.GetMessageCount();

                // Run through each of these messages and download the headers
                for (int messageIndex = messageCount; messageIndex > 0; messageIndex--)
                {
                    // If the Message ID of the current message is the same as the parameter given, delete that message                    
                    if (this.pop3Client.GetMessage(messageIndex).MessageId.Equals(messageId))
                    {
                        // gefunden, Nachricht laden
                        MimeMessage mailMessage = this.pop3Client.GetMessage(messageIndex);
                        foreach (MimeEntity attachment in mailMessage.Attachments)
                        {
                            if(attachment is MessagePart)
                            {
                                var filename = attachment.ContentDisposition?.FileName;
                                if ((filename != null) && filename.EndsWith(".pdf", StringComparison.OrdinalIgnoreCase))
                                    return attachment.ContentDisposition?.FileName;
                            }                            
                        }
                    }
                }
            }
            return null;
        }

        #endregion

        #region delete designated email

        /// <summary>
        /// deletes message referenced by messageId
        /// </summary>        
        /// <returns>true if successful</returns>
        public bool DeleteMessageByMessageId(string messageId)
        {
            if (!IsConnected) return false;

            // Get the number of messages on the POP3 server
            int messageCount = this.pop3Client.GetMessageCount();

            // Run trough each of these messages and download the headers
            for (int messageItem = (messageCount - 1); messageItem >= 0; messageItem--)
            {
                // If the Message ID of the current message is the same as the parameter given, delete that message
                if (this.pop3Client.GetMessage(messageItem).MessageId.Equals(messageId))
                {
                    // Delete
                    this.pop3Client.DeleteMessage(messageItem);
                    return true;
                }
            }

            // We did not find any message with the given messageId, report this back
            return false;            
        }

        #endregion

        #region MailKit helper / info / logging funcs

        #region SslConnectionInformation

        public static void PrintSslConnectionInfo()
        {
            using (var client = new SmtpClient())
            {
                string host = Properties.Settings.Default.SMTPServer;
                client.Connect(host, 587, SecureSocketOptions.Auto);

                Console.WriteLine($"Negotiated the following SSL options with {host}:");
                Console.WriteLine($"        Protocol Version: {client.SslProtocol}");
                Console.WriteLine($"        Cipher Algorithm: {client.SslCipherAlgorithm}");
                Console.WriteLine($"         Cipher Strength: {client.SslCipherStrength}");
                Console.WriteLine($"          Hash Algorithm: {client.SslHashAlgorithm}");
                Console.WriteLine($"           Hash Strength: {client.SslHashStrength}");
                Console.WriteLine($"  Key-Exchange Algorithm: {client.SslKeyExchangeAlgorithm}");
                Console.WriteLine($"   Key-Exchange Strength: {client.SslKeyExchangeStrength}");

                // Example Log:
                //
                // Negotiated the following SSL options with pop.gmail.com:
                //         Protocol Version: Tls12
                //         Cipher Algorithm: Aes128
                //          Cipher Strength: 128
                //           Hash Algorithm: Sha256
                //            Hash Strength: 0
                //   Key-Exchange Algorithm: 44550
                //    Key-Exchange Strength: 255

                client.Disconnect(true);
            }
        }

        public static void PrintCapabilities()
        {
            using (var client = new Pop3Client())
            {
                client.Connect(Properties.Settings.Default.POP3Server, Properties.Settings.Default.POP3Port, SecureSocketOptions.SslOnConnect);

                if (client.Capabilities.HasFlag(Pop3Capabilities.Sasl))
                {
                    var mechanisms = string.Join(", ", client.AuthenticationMechanisms);
                    Console.WriteLine("The POP3 server supports the following SASL mechanisms: {0}", mechanisms);
                }

                client.Authenticate(Properties.Settings.Default.POP3User, Properties.Settings.Default.POP3Password);

                if (client.Capabilities.HasFlag(Pop3Capabilities.Apop))
                    Console.WriteLine("The server supports APOP authentication.");

                if (client.Capabilities.HasFlag(Pop3Capabilities.Expire))
                {
                    if (client.ExpirePolicy > 0)
                        Console.WriteLine("The POP3 server automatically expires messages after {0} days", client.ExpirePolicy);
                    else
                        Console.WriteLine("The POP3 server will never expire messages.");
                }

                if (client.Capabilities.HasFlag(Pop3Capabilities.LoginDelay))
                    Console.WriteLine("The minimum number of seconds between login attempts is {0}.", client.LoginDelay);

                if (client.Capabilities.HasFlag(Pop3Capabilities.Pipelining))
                    Console.WriteLine("The POP3 server can pipeline commands, so using client.GetMessages() will be faster.");

                if (client.Capabilities.HasFlag(Pop3Capabilities.Top))
                    Console.WriteLine("The POP3 server supports the TOP command, so it's possible to download message headers.");

                if (client.Capabilities.HasFlag(Pop3Capabilities.UIDL))
                    Console.WriteLine("The POP3 server supports the UIDL command which means we can track messages by UID.");

                client.Disconnect(true);
            }
        }

        #endregion


        #endregion

    }
}