// This is a custom transport agent for sender based re-routing, created by Martin Tuescher
// As it is here, it needs a Send Connector configured to route mails to override domains that has equal or lower costs than the Default Send Connector for "*".

using System;
using System.IO;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Diagnostics;
using System.Configuration.Install;
using System.ComponentModel;
using Microsoft.Win32;

using Microsoft.Exchange.Data.Transport;
using Microsoft.Exchange.Data.Transport.Email;
using Microsoft.Exchange.Data.Transport.Smtp;
using Microsoft.Exchange.Data.Transport.Routing;
using Microsoft.Exchange.Data.Common;

namespace Microsoft.Exchange.SBR
{
    /// <summary>
    /// Run when installing the assembly, this function sets up the required 
    /// application event logging registry keys
    /// </summary>
    [RunInstaller(true)]
    public class SbrRoutingAgentEventLogInstaller : Installer
    {
        private EventLogInstaller SbrEventLogInstaller;

        public SbrRoutingAgentEventLogInstaller()
        {
            SbrEventLogInstaller = new EventLogInstaller();			// Create an instance of an EventLogInstaller.
            SbrEventLogInstaller.Source = "Microsoft.Exchange.SBR";	// Set the source name of the event log.
            SbrEventLogInstaller.Log = "Application";				// Set the event log that the source writes entries to.
            Installers.Add(SbrEventLogInstaller);					// Add routingeventLogInstaller to the Installer collection.

            RegistryKey newRegKey = Registry.LocalMachine.CreateSubKey("System\\CurrentControlSet\\Services\\MSExchangeSbrAgent\\Diagnostics");
            newRegKey.SetValue("General", 0);
        }
    }

    public sealed class SbrRoutingAgentFactory : RoutingAgentFactory
    {
        public override RoutingAgent CreateAgent(SmtpServer server)
        {
            RoutingAgent myAgent = new OwnRoutingAgent();
            return myAgent;
        }
    }

    public class OwnRoutingAgent : RoutingAgent
    {
        private int eventLogLevel = -1;     // Don't log if the proper keys aren't setup because this could cause problems later.
        private RegistryKey eventLogRegKey; // This is a member in case we want to add registry monitoring

        private Dictionary<String, String> _RoutingTable;
        private String OverrideSettingsFileName = Environment.GetEnvironmentVariable("ExchangeInstallPath", EnvironmentVariableTarget.Machine) + @"TransportRoles\agents\Custom\Microsoft.Exchange.SBR.OverrideSettings.config";

        private Dictionary<String, String> _InternalDomains;
        private String InternalDomainsFileName = Environment.GetEnvironmentVariable("ExchangeInstallPath", EnvironmentVariableTarget.Machine) + @"TransportRoles\agents\Custom\Microsoft.Exchange.SBR.InternalDomains.config";

        private String[] _IgnoreAuthAsValues;
        private String IgnoreAuthAsFileName = Environment.GetEnvironmentVariable("ExchangeInstallPath", EnvironmentVariableTarget.Machine) + @"TransportRoles\agents\Custom\Microsoft.Exchange.SBR.IgnoreAuthAs.config";

        public OwnRoutingAgent()
        {
            this.eventLogRegKey = Registry.LocalMachine.OpenSubKey("SYSTEM\\CurrentControlSet\\services\\MSExchangeSbrAgent\\Diagnostics");	// Read EventLogLevel from Registry
            if (this.eventLogRegKey != null)
            {
                if (eventLogRegKey.GetValue("General") != null)
                {
                    this.eventLogLevel = ((int)eventLogRegKey.GetValue("General"));

                    if (eventLogLevel >= 6) EventLog.WriteEntry("Microsoft.Exchange.SBR", "Event logging set to level " + this.eventLogLevel.ToString() + ".");
                }
            }

            //subscribe to different events
            base.OnResolvedMessage += new ResolvedMessageEventHandler(OwnRoutingAgent_OnResolvedMessage);

            _IgnoreAuthAsValues = File
                                  .ReadAllLines(IgnoreAuthAsFileName)
                                  .Where(line => !String.IsNullOrEmpty(line))
                                  .Where(line => !line.StartsWith("#"))
                                  .Select(line => line.ToLower())
                                  .ToArray();   // assumes line has 1 element, no error check

            _InternalDomains = File
                              .ReadAllLines(InternalDomainsFileName)
                              .Where(line => !String.IsNullOrEmpty(line))
                              .Where(line => !line.StartsWith("#"))
                              .Select(line => line.ToLower())
                              .Select(line => line.Split(';'))
                              .ToDictionary(items => items[0], items => items[1]); // assumes line has 2 elements, no error check

            _RoutingTable = File
                           .ReadAllLines(OverrideSettingsFileName)
                           .Where(line => !String.IsNullOrEmpty(line))
                           .Where(line => !line.StartsWith("#"))
                           .Select(line => line.ToLower())
                           .Select(line => line.Split(';'))
                           .ToDictionary(items => items[0], items => items[1]); // assumes line has 2 elements, no error check
        }

        private void OwnRoutingAgent_OnResolvedMessage(ResolvedMessageEventSource source, QueuedMessageEventArgs e)
        {
            try
            {
                var routingOverrideDomainPart = "";
                var senderFullEmailAddress = e.MailItem.FromAddress.ToString().ToLower();   // get full sender email address
                var senderOnlyDomainPart = e.MailItem.FromAddress.DomainPart.ToLower();     // get domain part of sender email address
                var emailMessageId = e.MailItem.Message.MessageId.ToString();
                var emailMessageSubject = e.MailItem.Message.Subject.ToString();
                Microsoft.Exchange.Data.Mime.Header emailMessageOrgAuthAs;
                emailMessageOrgAuthAs = e.MailItem.Message.MimeDocument.RootPart.Headers.FindFirst("X-MS-Exchange-Organization-AuthAs");

                if (eventLogLevel >= 4) EventLog.WriteEntry("Microsoft.Exchange.SBR", "Entering OnResolved for message " + emailMessageId + " (\"" + emailMessageSubject + "\").", EventLogEntryType.Information, 1);

                if (!_IgnoreAuthAsValues.Contains(emailMessageOrgAuthAs.Value.ToString().ToLower()))
                {
                    // X-MS-Exchange-Organization-AuthAs value not found in ignore table (typically "Internal") so we start processing the mail
                    if (eventLogLevel >= 5) EventLog.WriteEntry("Microsoft.Exchange.SBR", "\"X-MS-Exchange-Organization-AuthAs\" header for message " + emailMessageId + " (\"" + emailMessageSubject + "\"):\n" + emailMessageOrgAuthAs.Value.ToString().ToLower(), EventLogEntryType.Information, 1);
                    if (!_RoutingTable.ContainsKey(senderOnlyDomainPart) && !_RoutingTable.ContainsKey(senderFullEmailAddress))
                    {
                        // sender email domain or address not found in rerouting table, quit
                        if (eventLogLevel >= 4) EventLog.WriteEntry("Microsoft.Exchange.SBR", "Exiting OnResolved for message " + emailMessageId + " (\"" + emailMessageSubject + "\"):\nSender email domain or address not found in rerouting table.\nSBR agent is not processing this mail.", EventLogEntryType.Information, 8);
                        return;
                    }
                    else
                    {
                        // sender email domain or address found in rerouting table
                        int rerouteExternalCount = 0;
                        int rerouteInternalCount = 0;
                        int noRerouteCount = 0;
                        int totalCount = 0;

                        if (_RoutingTable.ContainsKey(senderOnlyDomainPart))
                        {
                            // sender email domain is in rerouting table
                            if (eventLogLevel >= 3) EventLog.WriteEntry("Microsoft.Exchange.SBR", "Sender email domain " + senderOnlyDomainPart + " for message " + emailMessageId + " (\"" + emailMessageSubject + "\") is in rerouting table.", EventLogEntryType.Information, 2);
                            routingOverrideDomainPart = _RoutingTable[senderOnlyDomainPart];
                        }

                        if (_RoutingTable.ContainsKey(senderFullEmailAddress))
                        {
                            // sender email address is in rerouting table
                            if (eventLogLevel >= 3) EventLog.WriteEntry("Microsoft.Exchange.SBR", "Sender email address " + senderFullEmailAddress + " for message " + emailMessageId + " (\"" + emailMessageSubject + "\") is in rerouting table.", EventLogEntryType.Information, 2);
                            routingOverrideDomainPart = _RoutingTable[senderFullEmailAddress];
                        }

                        var myRoutingOverride = new RoutingDomain(routingOverrideDomainPart);

                        foreach (EnvelopeRecipient recp in e.MailItem.Recipients)
                        {
                            if (_InternalDomains.ContainsKey(recp.Address.DomainPart.ToLower()))
                            {
                                // recipient domain is defined internal, now we have to look if GroupID is equal or not
                                if (_InternalDomains[senderOnlyDomainPart].Equals(_InternalDomains[recp.Address.DomainPart.ToLower()], StringComparison.OrdinalIgnoreCase))
                                {
                                    // No routing override, GroupID is equal
                                    if (eventLogLevel >= 2) EventLog.WriteEntry("Microsoft.Exchange.SBR", "Not overriding recipient " + recp.Address.ToString() + " on " + emailMessageId + " (\"" + emailMessageSubject + "\"):\nGroupID " + _InternalDomains[senderOnlyDomainPart].ToString().ToLower() + " is equal.", EventLogEntryType.Information, 4);
                                    noRerouteCount++;
                                }
                                else
                                {
                                    // Routing override, GroupID is not equal
                                    if (eventLogLevel >= 2) EventLog.WriteEntry("Microsoft.Exchange.SBR", "Overriding recipient " + recp.Address.ToString() + " on " + emailMessageId + " (\"" + emailMessageSubject + "\"):\nRecipient's GroupID " + _InternalDomains[recp.Address.DomainPart.ToLower()].ToString().ToLower() + " is not equal to sender's GroupID " + _InternalDomains[senderOnlyDomainPart].ToString().ToLower() + ".", EventLogEntryType.Information, 4);
                                    RoutingOverride newRoute = new RoutingOverride(myRoutingOverride, DeliveryQueueDomain.UseOverrideDomain);
                                    source.SetRoutingOverride(recp, newRoute);
                                    rerouteInternalCount++;
                                }
                            }
                            else
                            {
                                // recipient domain is not defined internal, so it must be external and routing overridden...
                                if (eventLogLevel >= 2) EventLog.WriteEntry("Microsoft.Exchange.SBR", "Overriding recipient " + recp.Address.ToString() + " on " + emailMessageId + " (\"" + emailMessageSubject + "\"):\nRecipient not defined internal.", EventLogEntryType.Information, 4);
                                RoutingOverride newRoute = new RoutingOverride(myRoutingOverride, DeliveryQueueDomain.UseOverrideDomain);
                                source.SetRoutingOverride(recp, newRoute);
                                rerouteExternalCount++;
                            }
                            totalCount++;
                        }

                        if (eventLogLevel >= 1) EventLog.WriteEntry("Microsoft.Exchange.SBR", "Statistics for message " + emailMessageId + " (\"" + emailMessageSubject + "\"):\n" + totalCount.ToString() + " recipients checked for rerouting.\n" + rerouteExternalCount.ToString() + " external recipients were rerouted.\n" + rerouteInternalCount.ToString() + " internal recipients were rerouted because GroupIDs were not equal.\n" + noRerouteCount.ToString() + " internal recipients were not rerouted because GroupIDs were equal.", EventLogEntryType.Information, 5);
                        if (eventLogLevel >= 4) EventLog.WriteEntry("Microsoft.Exchange.SBR", "Exiting OnResolved for message " + emailMessageId + " (\"" + emailMessageSubject + "\").", EventLogEntryType.Information, 8);
                    }
                }
                else
                {
                    // X-MS-Exchange-Organization-AuthAs value found in ignore table
                    if (eventLogLevel >= 4) EventLog.WriteEntry("Microsoft.Exchange.SBR", "Exiting OnResolved for message " + emailMessageId + " (\"" + emailMessageSubject + "\"):\nX-MS-Exchange-Organization-AuthAs header \"" + emailMessageOrgAuthAs.Value.ToString().ToLower() + "\" found in ignore table.\nSBR agent is not processing this mail.", EventLogEntryType.Information, 8);
                    return;
                }
            }
            catch (Exception except)
            {
                if (eventLogLevel >= 3) EventLog.WriteEntry("Microsoft.Exchange.SBR", "Exception (OnResolved): " + except.Message + "\n" + except.StackTrace, EventLogEntryType.Information, 10);
            }
        }
    }
}