Implement a general way to store selection data for gossip and fix trainer exploit

Game/Handlers/MailHandler.cs

@@ -367,6 +367,9 @@ namespace Game
         [WorldPacketHandler(ClientOpcodes.MailReturnToSender)]
         void HandleMailReturnToSender(MailReturnToSender packet)
         {
+            if (!CanOpenMailBox(_player.PlayerTalkClass.GetInteractionData().SourceGuid))
+                return;
+
             Player player = GetPlayer();
             Mail m = player.GetMail(packet.MailID);
             if (m == null || m.state == MailState.Deleted || m.deliver_time > Time.UnixTime || m.sender != packet.SenderGUID.GetCounter())
@@ -576,6 +579,8 @@ namespace Game
                     response.Mails.Add(new MailListEntry(m, player));
             }
 
+            player.PlayerTalkClass.GetInteractionData().Reset();
+            player.PlayerTalkClass.GetInteractionData().SourceGuid = packet.Mailbox;
             SendPacket(response);
 
             // recalculate m_nextMailDelivereTime and unReadMails

Game/Handlers/MiscHandler.cs

@@ -432,6 +432,12 @@ namespace Game
                 _player.Prestige();
         }
 
+        [WorldPacketHandler(ClientOpcodes.CloseInteraction, Processing = PacketProcessing.ThreadSafe)]
+        void HandleCloseInteraction(CloseInteraction packet)
+        {
+            _player.PlayerTalkClass.GetInteractionData().Reset();
+        }
+
         [WorldPacketHandler(ClientOpcodes.ChatUnregisterAllAddonPrefixes)]
         void HandleUnregisterAllAddonPrefixes(ChatUnregisterAllAddonPrefixes packet)
         {

Game/Handlers/NPCHandler.cs

@@ -79,7 +79,9 @@ namespace Game
                 return;
             }
 
-            _player.SetCurrentTrainerId(trainerId);
+            _player.PlayerTalkClass.GetInteractionData().Reset();
+            _player.PlayerTalkClass.GetInteractionData().SourceGuid = guid;
+            _player.PlayerTalkClass.GetInteractionData().TrainerId = trainerId;
             trainer.SendSpells(unit, _player, GetSessionDbLocaleIndex());
         }
 
@@ -97,7 +99,10 @@ namespace Game
             if (_player.HasUnitState(UnitState.Died))
                 _player.RemoveAurasByType(AuraType.FeignDeath);
 
-            if (_player.GetCurrentTrainerId() != packet.TrainerID)
+            if (_player.PlayerTalkClass.GetInteractionData().SourceGuid != packet.TrainerGUID)
+                return;
+
+            if (_player.PlayerTalkClass.GetInteractionData().TrainerId != packet.TrainerID)
                 return;
 
             // check present spell in trainer spell list
@@ -164,7 +169,7 @@ namespace Game
                 return;
 
             // Prevent cheating on C# scripted menus
-            if (GetPlayer().PlayerTalkClass.GetGossipMenu().GetSenderGUID() != packet.GossipUnit)
+            if (GetPlayer().PlayerTalkClass.GetInteractionData().SourceGuid != packet.GossipUnit)
                 return;
 
             Creature unit = null;