Core/AI: Fix crashes caused by charmed Creatures having null AI for 1 map update tick (#27434)

Implement using ScheduledChangeAI instead of nullptr to signal a required AI change

2 files changed, 23 insertions, 4 deletions

diff --git a/src/server/game/Entities/Unit/Unit.cpp b/src/server/game/Entities/Unit/Unit.cpp
index eda7b604fe6..278087e4890 100644
--- a/src/server/game/Entities/Unit/Unit.cpp
+++ b/src/server/game/Entities/Unit/Unit.cpp
@@ -60,6 +60,7 @@
 #include "PlayerAI.h"
 #include "QuestDef.h"
 #include "ReputationMgr.h"
+#include "ScheduledChangeAI.h"
 #include "SpellAuraEffects.h"
 #include "SpellAuras.h"
 #include "Spell.h"
@@ -491,7 +492,7 @@ void Unit::Update(uint32 p_time)
     // All position info based actions have been executed, reset info
     _positionUpdateInfo.Reset();
 
-    if (!GetAI() && (GetTypeId() != TYPEID_PLAYER || (IsCharmed() && GetCharmerGUID().IsCreature())))
+    if (HasScheduledAIChange() && (GetTypeId() != TYPEID_PLAYER || (IsCharmed() && GetCharmerGUID().IsCreature())))
         UpdateCharmAI();
     RefreshAI();
 }
@@ -9524,11 +9525,11 @@ void Unit::ScheduleAIChange()
     bool const charmed = IsCharmed();
 
     if (charmed)
-        PushAI(nullptr);
+        PushAI(GetScheduledChangeAI());
     else
     {
         RestoreDisabledAI();
-        PushAI(nullptr); //This could actually be PopAI() to get the previous AI but it's required atm to trigger UpdateCharmAI()
+        PushAI(GetScheduledChangeAI()); //This could actually be PopAI() to get the previous AI but it's required atm to trigger UpdateCharmAI()
     }
 }
 
@@ -9536,10 +9537,26 @@ void Unit::RestoreDisabledAI()
 {
     // Keep popping the stack until we either reach the bottom or find a valid AI
     while (PopAI())
-        if (GetTopAI())
+        if (GetTopAI() && dynamic_cast<ScheduledChangeAI*>(GetTopAI()) == nullptr)
             return;
 }
 
+UnitAI* Unit::GetScheduledChangeAI()
+{
+    if (Creature* creature = ToCreature())
+        return new ScheduledChangeAI(creature);
+    else
+        return nullptr;
+}
+
+bool Unit::HasScheduledAIChange() const
+{
+    if (UnitAI* ai = GetAI())
+        return dynamic_cast<ScheduledChangeAI*>(ai) != nullptr;
+    else
+        return true;
+}
+
 void Unit::AddToWorld()
 {
     if (IsInWorld())
diff --git a/src/server/game/Entities/Unit/Unit.h b/src/server/game/Entities/Unit/Unit.h
index ea63c22ea3a..07f46b6a7c7 100644
--- a/src/server/game/Entities/Unit/Unit.h
+++ b/src/server/game/Entities/Unit/Unit.h
@@ -804,6 +804,8 @@ class TC_GAME_API Unit : public WorldObject
         void SetAI(UnitAI* newAI);
         UnitAI* GetTopAI() const { return i_AIs.empty() ? nullptr : i_AIs.top().get(); }
         void RefreshAI();
+        UnitAI* GetScheduledChangeAI();
+        bool HasScheduledAIChange() const;
     public:
 
         void AddToWorld() override;