Core/Vehicle: Make the passenger join event asynchronous

Prevents a crash in the following scenario:
Player 1 enters vehicle X
Seat on vehicle X is taken by Player 2
Player 2 is removed from vehicle X
Vehicle X dismisses (but player 1 did not even finish AddPasssenger
call)

Fixes #4271

3 files changed, 139 insertions, 68 deletions

diff --git a/src/server/game/Entities/Unit/Unit.h b/src/server/game/Entities/Unit/Unit.h
index 1a41c25d97c..62facf6a69e 100644
--- a/src/server/game/Entities/Unit/Unit.h
+++ b/src/server/game/Entities/Unit/Unit.h
@@ -332,6 +332,7 @@ class UnitAI;
 class Totem;
 class Transport;
 class Vehicle;
+class VehicleJoinEvent;
 class TransportBase;
 class SpellCastTargets;
 
@@ -2183,6 +2184,7 @@ class Unit : public WorldObject
         uint32 GetRedirectThreatPercent() { return _redirectThreadInfo.GetThreatPct(); }
         Unit* GetRedirectThreatTarget() { return _redirectThreadInfo.GetTargetGUID() ? GetUnit(*this, _redirectThreadInfo.GetTargetGUID()) : NULL; }
 
+        friend class VehicleJoinEvent;
         bool IsAIEnabled, NeedChangeAI;
         bool CreateVehicleKit(uint32 id, uint32 creatureEntry);
         void RemoveVehicleKit();
diff --git a/src/server/game/Entities/Vehicle/Vehicle.cpp b/src/server/game/Entities/Vehicle/Vehicle.cpp
index 96f2b6d73dd..b6e47f239db 100755
--- a/src/server/game/Entities/Vehicle/Vehicle.cpp
+++ b/src/server/game/Entities/Vehicle/Vehicle.cpp
@@ -30,9 +30,10 @@
 #include "SpellInfo.h"
 #include "MoveSplineInit.h"
 #include "TemporarySummon.h"
+#include "EventProcessor.h"
 
 Vehicle::Vehicle(Unit* unit, VehicleEntry const* vehInfo, uint32 creatureEntry) :
-_me(unit), _vehicleInfo(vehInfo), _usableSeatNum(0), _creatureEntry(creatureEntry), _status(STATUS_NONE)
+_me(unit), _vehicleInfo(vehInfo), UsableSeatNum(0), _creatureEntry(creatureEntry), _status(STATUS_NONE)
 {
     for (uint32 i = 0; i < MAX_VEHICLE_SEATS; ++i)
     {
@@ -41,7 +42,7 @@ _me(unit), _vehicleInfo(vehInfo), _usableSeatNum(0), _creatureEntry(creatureEntr
             {
                 Seats.insert(std::make_pair(i, VehicleSeat(veSeat)));
                 if (veSeat->CanEnterOrExit())
-                    ++_usableSeatNum;
+                    ++UsableSeatNum;
             }
     }
 
@@ -123,10 +124,12 @@ void Vehicle::Uninstall()
             "Check Uninstall/PassengerBoarded script hooks for errors.", _me->GetGUIDLow(), _me->GetEntry());
         return;
     }
+
     _status = STATUS_UNINSTALLING;
     sLog->outDebug(LOG_FILTER_VEHICLES, "Vehicle::Uninstall Entry: %u, GuidLow: %u", _creatureEntry, _me->GetGUIDLow());
     RemoveAllPassengers();
 
+
     if (GetBase()->GetTypeId() == TYPEID_UNIT)
         sScriptMgr->OnUninstall(this);
 }
@@ -136,14 +139,14 @@ void Vehicle::Reset(bool evading /*= false*/)
     sLog->outDebug(LOG_FILTER_VEHICLES, "Vehicle::Reset Entry: %u, GuidLow: %u", _creatureEntry, _me->GetGUIDLow());
     if (_me->GetTypeId() == TYPEID_PLAYER)
     {
-        if (_usableSeatNum)
+        if (UsableSeatNum)
             _me->SetFlag(UNIT_NPC_FLAGS, UNIT_NPC_FLAG_PLAYER_VEHICLE);
     }
     else
     {
         ApplyAllImmunities();
         InstallAllAccessories(evading);
-        if (_usableSeatNum)
+        if (UsableSeatNum)
             _me->SetFlag(UNIT_NPC_FLAGS, UNIT_NPC_FLAG_SPELLCLICK);
     }
 
@@ -215,6 +218,19 @@ void Vehicle::RemoveAllPassengers()
     //    ASSERT(!itr->second.passenger);
 }
 
+void Vehicle::RemovePendingPassengers()
+{
+    sLog->outDebug(LOG_FILTER_VEHICLES, "Vehicle::RemovePendingPassengers. Entry: %u, GuidLow: %u", _creatureEntry, _me->GetGUIDLow());
+
+    /// Setting to_Abort to true will cause @VehicleJoinEvent::Abort to be executed on next @Unit::UpdateEvents call
+    /// This will properly "reset" the pending join process for the passenger.
+    while (VehicleJoinEvent* e = _pendingJoinEvents.front())
+    {
+        e->to_Abort = true;
+        _pendingJoinEvents.pop_front();
+    }
+}
+
 bool Vehicle::HasEmptySeat(int8 seatId) const
 {
     SeatMap::const_iterator seat = Seats.find(seatId);
@@ -317,7 +333,17 @@ bool Vehicle::AddPassenger(Unit* unit, int8 seatId)
     if (unit->GetVehicle() != this)
         return false;
 
+    // The seat selection code may kick other passengers off the vehicle.
+    // While the validity of the following may be arguable, it is possible that when such a passenger
+    // exits the vehicle will dismiss. That's why the actual adding the passenger to the vehicle is scheduled
+    // asynchronously, so it can be cancelled easily in case the vehicle is uninstalled meanwhile.
     SeatMap::iterator seat;
+    sLog->outDebug(LOG_FILTER_VEHICLES, "Unit %s scheduling enter vehicle entry %u id %u dbguid %u seat %d", 
+        unit->GetName().c_str(), _me->GetEntry(), _vehicleInfo->m_ID, _me->GetGUIDLow(), (int32)seat->first);
+    VehicleJoinEvent* e = new VehicleJoinEvent(this, unit, seat);
+    unit->m_Events.AddEvent(e, unit->m_Events.CalculateTime(0));
+    _pendingJoinEvents.push_back(e);
+
     if (seatId < 0) // no specific seat requirement
     {
         for (seat = Seats.begin(); seat != Seats.end(); ++seat)
@@ -325,13 +351,19 @@ bool Vehicle::AddPassenger(Unit* unit, int8 seatId)
                 break;
 
         if (seat == Seats.end()) // no available seat
+        {
+            CancelJoinEvent(e);
             return false;
+        }
     }
     else
     {
         seat = Seats.find(seatId);
         if (seat == Seats.end())
+        {
+            CancelJoinEvent(e);
             return false;
+        }
 
         if (seat->second.Passenger)
         {
@@ -344,65 +376,6 @@ bool Vehicle::AddPassenger(Unit* unit, int8 seatId)
         ASSERT(!seat->second.Passenger);
     }
 
-    sLog->outDebug(LOG_FILTER_VEHICLES, "Unit %s enter vehicle entry %u id %u dbguid %u seat %d", unit->GetName().c_str(), _me->GetEntry(), _vehicleInfo->m_ID, _me->GetGUIDLow(), (int32)seat->first);
-
-    seat->second.Passenger = unit->GetGUID();
-    if (seat->second.SeatInfo->CanEnterOrExit())
-    {
-        ASSERT(_usableSeatNum);
-        --_usableSeatNum;
-        if (!_usableSeatNum)
-        {
-            if (_me->GetTypeId() == TYPEID_PLAYER)
-                _me->RemoveFlag(UNIT_NPC_FLAGS, UNIT_NPC_FLAG_PLAYER_VEHICLE);
-            else
-                _me->RemoveFlag(UNIT_NPC_FLAGS, UNIT_NPC_FLAG_SPELLCLICK);
-        }
-    }
-
-    if (seat->second.SeatInfo->m_flags && !(seat->second.SeatInfo->m_flags & VEHICLE_SEAT_FLAG_ALLOW_TURNING))
-        unit->AddUnitState(UNIT_STATE_ONVEHICLE);
-
-    unit->AddUnitMovementFlag(MOVEMENTFLAG_ONTRANSPORT);
-    VehicleSeatEntry const* veSeat = seat->second.SeatInfo;
-    unit->m_movementInfo.t_pos.m_positionX = veSeat->m_attachmentOffsetX;
-    unit->m_movementInfo.t_pos.m_positionY = veSeat->m_attachmentOffsetY;
-    unit->m_movementInfo.t_pos.m_positionZ = veSeat->m_attachmentOffsetZ;
-    unit->m_movementInfo.t_pos.SetOrientation(0);
-    unit->m_movementInfo.t_time = 0; // 1 for player
-    unit->m_movementInfo.t_seat = seat->first;
-    unit->m_movementInfo.t_guid = _me->GetGUID();
-
-    if (_me->GetTypeId() == TYPEID_UNIT && unit->GetTypeId() == TYPEID_PLAYER &&
-        seat->second.SeatInfo->m_flags & VEHICLE_SEAT_FLAG_CAN_CONTROL)
-        ASSERT(_me->SetCharmedBy(unit, CHARM_TYPE_VEHICLE))
-
-    if (_me->IsInWorld())
-    {
-        unit->SendClearTarget();                            // SMSG_BREAK_TARGET
-        unit->SetControlled(true, UNIT_STATE_ROOT);         // SMSG_FORCE_ROOT - In some cases we send SMSG_SPLINE_MOVE_ROOT here (for creatures)
-                                                            // also adds MOVEMENTFLAG_ROOT
-        Movement::MoveSplineInit init(unit);
-        init.DisableTransportPathTransformations();
-        init.MoveTo(veSeat->m_attachmentOffsetX, veSeat->m_attachmentOffsetY, veSeat->m_attachmentOffsetZ);
-        init.SetFacing(0.0f);
-        init.SetTransportEnter();
-        init.Launch();
-
-        if (_me->GetTypeId() == TYPEID_UNIT)
-        {
-            if (_me->ToCreature()->IsAIEnabled)
-                _me->ToCreature()->AI()->PassengerBoarded(unit, seat->first, true);
-
-            // update all passenger's positions
-            //Passenger's spline OR vehicle movement will update positions
-            //RelocatePassengers(_me->GetPositionX(), _me->GetPositionY(), _me->GetPositionZ(), _me->GetOrientation());
-        }
-    }
-
-    if (GetBase()->GetTypeId() == TYPEID_UNIT)
-        sScriptMgr->OnAddPassenger(this, unit, seatId);
-
     return true;
 }
 
@@ -419,14 +392,14 @@ void Vehicle::RemovePassenger(Unit* unit)
     seat->second.Passenger = 0;
     if (seat->second.SeatInfo->CanEnterOrExit())
     {
-        if (!_usableSeatNum)
+        if (!UsableSeatNum)
         {
             if (_me->GetTypeId() == TYPEID_PLAYER)
                 _me->SetFlag(UNIT_NPC_FLAGS, UNIT_NPC_FLAG_PLAYER_VEHICLE);
             else
                 _me->SetFlag(UNIT_NPC_FLAGS, UNIT_NPC_FLAG_SPELLCLICK);
         }
-        ++_usableSeatNum;
+        ++UsableSeatNum;
     }
 
     unit->ClearUnitState(UNIT_STATE_ONVEHICLE);
@@ -549,3 +522,78 @@ void Vehicle::CalculatePassengerOffset(float& x, float& y, float& z, float& o)
     y = (iny - inx * tan(GetBase()->GetOrientation())) / (cos(GetBase()->GetOrientation()) + std::sin(GetBase()->GetOrientation()) * tan(GetBase()->GetOrientation()));
     x = (inx + iny * tan(GetBase()->GetOrientation())) / (cos(GetBase()->GetOrientation()) + std::sin(GetBase()->GetOrientation()) * tan(GetBase()->GetOrientation()));
 }
+    
+void Vehicle::CancelJoinEvent(VehicleJoinEvent* e)
+{
+    e->to_Abort = true;
+    _pendingJoinEvents.pop_back();
+}
+
+bool VehicleJoinEvent::Execute(uint64, uint32)
+{
+    ASSERT(Passenger->GetVehicle() == Target);
+
+    Seat->second.Passenger = Passenger->GetGUID();
+    if (Seat->second.SeatInfo->CanEnterOrExit())
+    {
+        ASSERT(Target->UsableSeatNum);
+        --(Target->UsableSeatNum);
+        if (!Target->UsableSeatNum)
+        {
+            if (Target->GetBase()->GetTypeId() == TYPEID_PLAYER)
+                Target->GetBase()->RemoveFlag(UNIT_NPC_FLAGS, UNIT_NPC_FLAG_PLAYER_VEHICLE);
+            else
+                Target->GetBase()->RemoveFlag(UNIT_NPC_FLAGS, UNIT_NPC_FLAG_SPELLCLICK);
+        }
+    }
+
+    if (Seat->second.SeatInfo->m_flags && !(Seat->second.SeatInfo->m_flags & VEHICLE_SEAT_FLAG_ALLOW_TURNING))
+        Passenger->AddUnitState(UNIT_STATE_ONVEHICLE);
+
+    Passenger->AddUnitMovementFlag(MOVEMENTFLAG_ONTRANSPORT);
+    VehicleSeatEntry const* veSeat = Seat->second.SeatInfo;
+    Passenger->m_movementInfo.t_pos.m_positionX = veSeat->m_attachmentOffsetX;
+    Passenger->m_movementInfo.t_pos.m_positionY = veSeat->m_attachmentOffsetY;
+    Passenger->m_movementInfo.t_pos.m_positionZ = veSeat->m_attachmentOffsetZ;
+    Passenger->m_movementInfo.t_pos.SetOrientation(0.0f);
+    Passenger->m_movementInfo.t_time = 0; // 1 for player
+    Passenger->m_movementInfo.t_seat = Seat->first;
+    Passenger->m_movementInfo.t_guid = Target->GetBase()->GetGUID();
+
+    if (Target->GetBase()->GetTypeId() == TYPEID_UNIT && Passenger->GetTypeId() == TYPEID_PLAYER &&
+        Seat->second.SeatInfo->m_flags & VEHICLE_SEAT_FLAG_CAN_CONTROL)
+        ASSERT(Target->GetBase()->SetCharmedBy(Passenger, CHARM_TYPE_VEHICLE))
+
+    if (Target->GetBase()->IsInWorld())
+    {
+        Passenger->SendClearTarget();                            // SMSG_BREAK_TARGET
+        Passenger->SetControlled(true, UNIT_STATE_ROOT);         // SMSG_FORCE_ROOT - In some cases we send SMSG_SPLINE_MOVE_ROOT here (for creatures)
+        // also adds MOVEMENTFLAG_ROOT
+        Movement::MoveSplineInit init(Passenger);
+        init.DisableTransportPathTransformations();
+        init.MoveTo(veSeat->m_attachmentOffsetX, veSeat->m_attachmentOffsetY, veSeat->m_attachmentOffsetZ);
+        init.SetFacing(0.0f);
+        init.SetTransportEnter();
+        init.Launch();
+
+        if (Target->GetBase()->GetTypeId() == TYPEID_UNIT)
+        {
+            if (Target->GetBase()->ToCreature()->IsAIEnabled)
+                Target->GetBase()->ToCreature()->AI()->PassengerBoarded(Passenger, Seat->first, true);
+
+            // update all passenger's positions
+            //Passenger's spline OR vehicle movement will update positions
+            //RelocatePassengers(_me->GetPositionX(), _me->GetPositionY(), _me->GetPositionZ(), _me->GetOrientation());
+        }
+    }
+
+    if (Target->GetBase()->GetTypeId() == TYPEID_UNIT)
+        sScriptMgr->OnAddPassenger(Target, Passenger, Seat->first);
+
+    return true; 
+}
+    
+void VehicleJoinEvent::Abort(uint64)
+{
+    Passenger->m_vehicle = NULL;
+}
diff --git a/src/server/game/Entities/Vehicle/Vehicle.h b/src/server/game/Entities/Vehicle/Vehicle.h
index 823fb72b8a8..f8fa7f9b64a 100644
--- a/src/server/game/Entities/Vehicle/Vehicle.h
+++ b/src/server/game/Entities/Vehicle/Vehicle.h
@@ -23,12 +23,12 @@
 #include "Object.h"
 #include "VehicleDefines.h"
 #include "Unit.h"
+#include <deque>
 
 struct VehicleEntry;
-
 class Unit;
-
 typedef std::set<uint64> GuidSet;
+class VehicleJoinEvent;
 
 class Vehicle : public TransportBase
 {
@@ -54,6 +54,7 @@ class Vehicle : public TransportBase
         void RemovePassenger(Unit* passenger);
         void RelocatePassengers();
         void RemoveAllPassengers();
+        void RemovePendingPassengers();
         void Dismiss();
         void TeleportVehicle(float x, float y, float z, float ang);
         bool IsVehicleInUse() { return Seats.begin() != Seats.end(); }
@@ -66,6 +67,10 @@ class Vehicle : public TransportBase
         VehicleSeatEntry const* GetSeatForPassenger(Unit* passenger);
 
     protected:
+        friend class VehicleJoinEvent;
+        uint32 UsableSeatNum;         // Number of seats that match VehicleSeatEntry::UsableByPlayer, used for proper display flags
+
+    protected:
         friend bool Unit::CreateVehicleKit(uint32 id, uint32 creatureEntry);
         Vehicle(Unit* unit, VehicleEntry const* vehInfo, uint32 creatureEntry);
         friend void Unit::RemoveVehicleKit();
@@ -91,9 +96,25 @@ class Vehicle : public TransportBase
         Unit* _me;
         VehicleEntry const* _vehicleInfo;
         GuidSet vehiclePlayers;
-        uint32 _usableSeatNum;         // Number of seats that match VehicleSeatEntry::UsableByPlayer, used for proper display flags
+        
         uint32 _creatureEntry;         // Can be different than me->GetBase()->GetEntry() in case of players
         Status _status;
         Position m_lastShootPos;
+
+        std::deque<VehicleJoinEvent*> _pendingJoinEvents;
+        void CancelJoinEvent(VehicleJoinEvent* e);
+};
+
+class VehicleJoinEvent : public BasicEvent
+{
+    friend class Vehicle;
+    protected:
+        VehicleJoinEvent(Vehicle* v, Unit* u, SeatMap::iterator& itr) : Target(v), Passenger(u), Seat(itr) {}
+        bool Execute(uint64, uint32);
+        void Abort(uint64);
+
+        Vehicle* Target;
+        Unit* Passenger;
+        SeatMap::iterator& Seat;
 };
 #endif