Core/AI: Clean up charm AI handling.

Port From (https://github.com/TrinityCore/TrinityCore/commit/e4e8c1c59c8b37216814526b4d2551f23934f465)

Source/Game/AI/CoreAI/CombatAI.cs

@@ -322,11 +322,12 @@ namespace Game.AI
 
         public override void AttackStart(Unit victim) { }
 
-        public override void OnCharmed(bool apply)
+        public override void OnCharmed(bool isNew)
         {
-            if (!me.GetVehicleKit().IsVehicleInUse() && !apply && _hasConditions)//was used and has conditions
+            bool charmed = me.IsCharmed();
+            if (!me.GetVehicleKit().IsVehicleInUse() && !charmed && _hasConditions)//was used and has conditions
                 _doDismiss = true;//needs reset
-            else if (apply)
+            else if (charmed)
                 _doDismiss = false;//in use again
 
             _dismissTimer = VEHICLE_DISMISS_TIME;//reset timer

Source/Game/AI/CoreAI/CreatureAI.cs

@@ -44,13 +44,20 @@ namespace Game.AI
             _moveInLineOfSightLocked = false;
         }
 
-        public override void OnCharmed(bool apply)
+        public override void OnCharmed(bool isNew)
         {
-            if (apply)
+            if (isNew && !me.IsCharmed() && !me.LastCharmerGUID.IsEmpty())
             {
-                me.NeedChangeAI = true;
-                me.IsAIEnabled = false;
+                if (!me.HasReactState(ReactStates.Passive))
+                {
+                    Unit lastCharmer = Global.ObjAccessor.GetUnit(me, me.LastCharmerGUID);
+                    if (lastCharmer != null)
+                        me.EngageWithTarget(lastCharmer);
+                }
+                me.LastCharmerGUID.Clear();
             }
+
+            base.OnCharmed(isNew);
         }
 
         public void Talk(uint id, WorldObject whisperTarget = null)

Source/Game/AI/CoreAI/PassiveAI.cs

@@ -76,12 +76,6 @@ namespace Game.AI
                 me.RemoveDynamicFlag(UnitDynFlags.Lootable);
         }
 
-        public override void OnCharmed(bool apply)
-        {
-            me.NeedChangeAI = true;
-            me.IsAIEnabled = false;
-        }
-
         public override void MoveInLineOfSight(Unit who) { }
 
         public override void EnterEvadeMode(EvadeReason why) { }
@@ -98,7 +92,7 @@ namespace Game.AI
         public override void AttackStart(Unit unit) { }
         public override void UpdateAI(uint diff) { }
         public override void EnterEvadeMode(EvadeReason why) { }
-        public override void OnCharmed(bool apply) { }
+        public override void OnCharmed(bool isNew) { }
     }
 
     public class CritterAI : PassiveAI

Source/Game/AI/CoreAI/PetAI.cs

@@ -601,12 +601,6 @@ namespace Game.AI
                 }
         }
 
-        public override void OnCharmed(bool apply)
-        {
-            me.NeedChangeAI = true;
-            me.IsAIEnabled = false;
-        }
-
         void ClearCharmInfoFlags()
         {
             // Quick access to set all flags to FALSE

Source/Game/AI/CoreAI/UnitAI.cs

@@ -463,7 +463,18 @@ namespace Game.AI
 
         public virtual void Reset() { }
 
-        public virtual void OnCharmed(bool apply) { }
+        /// <summary>
+        // Called when unit's charm state changes with isNew = false
+        // Implementation should call me->ScheduleAIChange() if AI replacement is desired
+        // If this call is made, AI will be replaced on the next tick
+        // When replacement is made, OnCharmed is called with isNew = true
+        /// </summary>
+        /// <param name="apply"></param>
+        public virtual void OnCharmed(bool isNew)
+        {
+            if (!isNew)
+                me.ScheduleAIChange();
+        }
 
         public virtual bool ShouldSparWith(Unit target) { return false; }