Core/AI: Finally move the "is creature engaged" flag to be a property of the creature AI, where it honestly always belonged.

Port From (https://github.com/TrinityCore/TrinityCore/commit/c13d83796f7b2111c5dcf8546bdd84eccd232ae3)

Source/Game/AI/CoreAI/CreatureAI.cs

@@ -29,6 +29,7 @@ namespace Game.AI
 {
     public class CreatureAI : UnitAI
     {
+        bool _isEngaged;
         bool _moveInLOSLocked;
         List<AreaBoundary> _boundary = new();
         bool _negateBoundary;
@@ -201,6 +202,12 @@ namespace Game.AI
             }
         }
 
+        public override void JustEnteredCombat(Unit who)
+        {
+            if (!IsEngaged() && !me.CanHaveThreatList())
+                EngagementStart(who);
+        }
+
         // Called for reaction at stopping attack at no attackers or targets
         public virtual void EnterEvadeMode(EvadeReason why = EvadeReason.Other)
         {
@@ -231,7 +238,7 @@ namespace Game.AI
 
         public bool UpdateVictim()
         {
-            if (!me.IsEngaged())
+            if (!IsEngaged())
                 return false;
 
             if (!me.HasReactState(ReactStates.Passive))
@@ -254,23 +261,53 @@ namespace Game.AI
             return true;
         }
 
+        public void EngagementStart(Unit who)
+        {
+            if (_isEngaged)
+            {
+                //Log.outError(LogFilter.ScriptsAi, $"CreatureAI::EngagementStart called even though creature is already engaged. Creature debug info:\n{me.GetDebugInfo()}");
+                return;
+            }
+            _isEngaged = true;
+
+            me.AtEngage(who);
+        }
+
+        public void EngagementOver()
+        {
+            if (!_isEngaged)
+            {
+                //Log.outError(LogFilter.ScriptsAi, $"CreatureAI::EngagementOver called even though creature is not currently engaged. Creature debug info:\n{me.GetDebugInfo()}");
+                return;
+            }
+            _isEngaged = false;
+
+            me.AtDisengage();
+        }
+
         public bool _EnterEvadeMode(EvadeReason why = EvadeReason.Other)
         {
-            if (!me.IsAlive())
+            if (me.IsInEvadeMode())
                 return false;
 
+            if (!me.IsAlive())
+            {
+                EngagementOver();
+                return false;
+            }
+
             me.RemoveAurasOnEvade();
 
             // sometimes bosses stuck in combat?
             me.CombatStop(true);
-            me.GetThreatManager().NotifyDisengaged();
             me.SetLootRecipient(null);
             me.ResetPlayerDamageReq();
             me.SetLastDamagedTime(0);
             me.SetCannotReachTarget(false);
             me.DoNotReacquireTarget();
+            EngagementOver();
 
-            return !me.IsInEvadeMode();
+            return true;
         }
 
         public CypherStrings VisualizeBoundary(int duration, Unit owner = null, bool fill = false)
@@ -404,11 +441,22 @@ namespace Game.AI
             me.DoImmediateBoundaryCheck();
         }
 
+        // Called for reaction whenever a new non-offline unit is added to the threat list
+        public virtual void JustStartedThreateningMe(Unit who)
+        {
+            if (!IsEngaged())
+                EngagementStart(who);
+        }
+
         // Called for reaction when initially engaged - this will always happen _after_ JustEnteredCombat
         public virtual void JustEngagedWith(Unit who) { }
 
         // Called when the creature is killed
-        public virtual void JustDied(Unit killer) { }
+        public virtual void JustDied(Unit killer) 
+        {
+            if (IsEngaged())
+                EngagementOver();
+        }
 
         // Called when the creature kills a unit
         public virtual void KilledUnit(Unit victim) { }
@@ -521,6 +569,8 @@ namespace Game.AI
         public virtual bool IsEscortNPC(bool onlyIfActive) { return false; }
 
         public List<AreaBoundary> GetBoundary() { return _boundary; }
+
+        public bool IsEngaged() { return _isEngaged; }
     }
 
     public class AISpellInfoType

Source/Game/AI/CoreAI/GuardAI.cs

@@ -48,7 +48,7 @@ namespace Game.AI
             {
                 me.GetMotionMaster().MoveIdle();
                 me.CombatStop(true);
-                me.GetThreatManager().NotifyDisengaged();
+                EngagementOver();
                 return;
             }
 
@@ -56,7 +56,7 @@ namespace Game.AI
 
             me.RemoveAllAuras();
             me.CombatStop(true);
-            me.GetThreatManager().NotifyDisengaged();
+            EngagementOver();
 
             me.GetMotionMaster().MoveTargetedHome();
         }

Source/Game/AI/CoreAI/PassiveAI.cs

@@ -77,6 +77,21 @@ namespace Game.AI
 
         public override void MoveInLineOfSight(Unit who) { }
 
+        public override void JustEnteredCombat(Unit who)
+        {
+            EngagementStart(who);
+        }
+
+        public override void JustExitedCombat()
+        {
+            EngagementOver();
+        }
+
+        public override void JustStartedThreateningMe(Unit who)
+        {
+
+        }
+
         public override void EnterEvadeMode(EvadeReason why) { }
     }
 
@@ -89,6 +104,8 @@ namespace Game.AI
 
         public override void MoveInLineOfSight(Unit unit) { }
         public override void AttackStart(Unit unit) { }
+        public override  void JustStartedThreateningMe(Unit unit)  { }
+        public override void JustEnteredCombat(Unit who) { }
         public override void UpdateAI(uint diff) { }
         public override void JustAppeared() { }
         public override void EnterEvadeMode(EvadeReason why) { }

Source/Game/AI/CoreAI/TotemAI.cs

@@ -21,7 +21,7 @@ using Game.Maps;
 
 namespace Game.AI
 {
-    public class TotemAI : CreatureAI
+    public class TotemAI : NullCreatureAI
     {
         ObjectGuid _victimGuid;
 
@@ -30,15 +30,6 @@ namespace Game.AI
             _victimGuid = ObjectGuid.Empty;
         }
 
-        public override void MoveInLineOfSight(Unit who) { }
-
-        public override void JustAppeared() { }
-
-        public override void EnterEvadeMode(EvadeReason why)
-        {
-            me.CombatStop(true);
-        }
-
         public override void UpdateAI(uint diff)
         {
             if (me.ToTotem().GetTotemType() != TotemType.Active)

Source/Game/AI/CoreAI/UnitAI.cs

@@ -536,7 +536,7 @@ namespace Game.AI
             _me = unit;
             _dist = dist;
             _playerOnly = playerOnly;
-            _exception = !withTank ? _me.GetThreatManager().GetCurrentVictim() : null;
+            _exception = !withTank ? unit.GetThreatManager().GetLastVictim() : null;
             _aura = aura;
         }
 

Source/Game/AI/ScriptedAI/ScriptedEscortAI.cs

@@ -135,9 +135,10 @@ namespace Game.AI
         {
             me.RemoveAllAuras();
             me.CombatStop(true);
-            me.GetThreatManager().NotifyDisengaged();
             me.SetLootRecipient(null);
 
+            EngagementOver();
+
             if (HasEscortState(EscortState.Escorting))
             {
                 AddEscortState(EscortState.Returning);

Source/Game/AI/ScriptedAI/ScriptedFollowerAI.cs

@@ -123,15 +123,19 @@ namespace Game.AI
         public override void EnterEvadeMode(EvadeReason why)
         {
             if (!me.IsAlive())
+            {
+                EngagementOver();
                 return;
+            }
 
             me.RemoveAllAuras();
             me.CombatStop(true);
-            me.GetThreatManager().NotifyDisengaged();
             me.SetLootRecipient(null);
             me.SetCannotReachTarget(false);
             me.DoNotReacquireTarget();
 
+            EngagementOver();
+
             if (HasFollowState(FollowState.Inprogress))
             {
                 Log.outDebug(LogFilter.Scripts, "FollowerAI left combat, returning to CombatStartPosition.");

Source/Game/Combat/CombatManager.cs

@@ -234,15 +234,9 @@ namespace Game.Combat
 
         public static void NotifyAICombat(Unit me, Unit other)
         {
-            if (!me.IsAIEnabled())
+            UnitAI ai = me.GetAI();
-                return;
+            if (ai != null)
-
+                ai.JustEnteredCombat(other);
-            me.GetAI().JustEnteredCombat(other);
-
-            Creature cMe = me.ToCreature();
-            if (cMe != null)
-                if (!cMe.CanHaveThreatList())
-                    cMe.GetAI().JustEngagedWith(other);
         }
 
         void PutReference(ObjectGuid guid, CombatReference refe)
@@ -277,14 +271,14 @@ namespace Game.Combat
             {
                 _owner.AddUnitFlag(UnitFlags.InCombat);
                 _owner.AtEnterCombat();
-                if (!_owner.CanHaveThreatList() && !_owner.IsEngaged())
+                if (_owner.IsCreature())
                     _owner.AtEngage(GetAnyTarget());
             }
             else
             {
                 _owner.RemoveUnitFlag(UnitFlags.InCombat);
                 _owner.AtExitCombat();
-                if (_owner.IsEngaged() && !(_owner.IsCreature() && _owner.CanHaveThreatList() && _owner.ToCreature().IsAIEnabled()))
+                if (!_owner.IsCreature())
                     _owner.AtDisengage();
             }
 

Source/Game/Combat/ThreatManager.cs

@@ -37,6 +37,7 @@ namespace Game.Combat
         uint _updateTimer;
         List<ThreatReference> _sortedThreatList = new();
         Dictionary<ObjectGuid, ThreatReference> _myThreatListEntries = new();
+        List<ThreatReference> _needsAIUpdate = new();
         ThreatReference _currentVictimRef;
         ThreatReference _fixateRef;
 
@@ -98,6 +99,12 @@ namespace Game.Combat
             if (_currentVictimRef == null || _currentVictimRef.ShouldBeOffline())
                 UpdateVictim();
 
+            Cypher.Assert(_currentVictimRef == null || _currentVictimRef.IsAvailable());
+            return _currentVictimRef?.GetVictim();
+        }
+
+        public Unit GetLastVictim()
+        {
             if (_currentVictimRef != null && !_currentVictimRef.ShouldBeOffline())
                 return _currentVictimRef.GetVictim();
 
@@ -294,7 +301,7 @@ namespace Game.Combat
                     }
                 }
 
-            if (targetRefe.IsOnline())
+                if (targetRefe.IsOnline())
                     targetRefe.AddThreat(amount);
                 return;
             }
@@ -306,14 +313,13 @@ namespace Game.Combat
 
             // afterwards, we evaluate whether this is an online reference (it might not be an acceptable target, but we need to add it to our threat list before we check!)
             newRefe.UpdateOffline();
-            if (newRefe.IsOnline()) // ...and if the ref is online it also gets the threat it should have
+            if (newRefe.IsOnline()) // we only add the threat if the ref is currently available
                 newRefe.AddThreat(amount);
 
-            if (!_owner.IsEngaged())
+            if (_currentVictimRef == null)
-            {
-                _owner.AtEngage(target);
                 UpdateVictim();
-            }
+            else
+                ProcessAIUpdates();
         }
 
         void ScaleThreat(Unit target, float factor)
@@ -398,18 +404,6 @@ namespace Game.Combat
             }
         }
 
-        /// <summary>
-        /// THIS SHOULD ONLY BE CALLED FROM A CREATURE'S AI (typically in EnterEvadeMode)
-        /// notify the unit that the AI has disengaged
-        /// </summary>
-        public void NotifyDisengaged()
-        {
-            // note: i don't really like having this here
-            // (maybe engage flag should be in creature ai? it's inherently an AI property...)
-            if (_owner.IsEngaged())
-                _owner.AtDisengage();
-        }
-
         public void FixateTarget(Unit target)
         {
             if (target)
@@ -446,6 +440,7 @@ namespace Game.Combat
                 NeedClientUpdate = false;
             }
 
+            ProcessAIUpdates();
         }
 
         ThreatReference ReselectVictim()
@@ -454,7 +449,7 @@ namespace Game.Combat
                 return null;
 
             foreach (var pair in _myThreatListEntries)
-                pair.Value.UpdateOffline();
+                pair.Value.UpdateOffline(); // AI notifies are processed in ::UpdateVictim caller
 
             // fixated target is always preferred
             if (_fixateRef != null && _fixateRef.IsAvailable())
@@ -509,6 +504,16 @@ namespace Game.Combat
             return null;
         }
 
+        void ProcessAIUpdates()
+        {
+            CreatureAI ai = _owner.ToCreature().GetAI();
+            List<ThreatReference> v = new(_needsAIUpdate); // _needClientUpdate is now empty in case this triggers a recursive call
+            if (ai == null)
+                return;
+            foreach (ThreatReference refe in v)
+                ai.JustStartedThreateningMe(refe.GetVictim());
+        }
+
         // returns true if a is LOWER on the threat list than b
         public static bool CompareReferencesLT(ThreatReference a, ThreatReference b, float aWeight)
         {
@@ -563,17 +568,17 @@ namespace Game.Combat
                     threat *= victimMgr._singleSchoolModifiers[(int)SpellSchools.Arcane];
                     break;
                 default:
+                {
+                    if (victimMgr._multiSchoolModifiers.TryGetValue(mask, out float value))
                     {
-                        if (victimMgr._multiSchoolModifiers.TryGetValue(mask, out float value))
+                        threat *= value;
-                        {
-                            threat *= value;
-                            break;
-                        }
-                        float mod = victim.GetTotalAuraMultiplierByMiscMask(AuraType.ModThreat, (uint)mask);
-                        victimMgr._multiSchoolModifiers[mask] = mod;
-                        threat *= mod;
                         break;
                     }
+                    float mod = victim.GetTotalAuraMultiplierByMiscMask(AuraType.ModThreat, (uint)mask);
+                    victimMgr._multiSchoolModifiers[mask] = mod;
+                    threat *= mod;
+                    break;
+                }
             }
             return threat;
         }
@@ -671,7 +676,7 @@ namespace Game.Combat
             threatClear.UnitGUID = _owner.GetGUID();
             _owner.SendMessageToSet(threatClear, false);
         }
-        
+
         public void SendRemoveToClients(Unit victim)
         {
             ThreatRemove threatRemove = new();
@@ -797,6 +802,8 @@ namespace Game.Combat
 
         // Resets the specified unit's threat to zero
         public void ResetThreat(Unit target) { ScaleThreat(target, 0.0f); }
+
+        public void RegisterForAIUpdate(ThreatReference refe) { _needsAIUpdate.Add(refe); }
     }
 
     public enum TauntState
@@ -827,7 +834,7 @@ namespace Game.Combat
             _owner = mgr._owner as Creature;
             _mgr = mgr;
             _victim = victim;
-            Online = ShouldBeSuppressed() ? OnlineState.Suppressed : OnlineState.Online;
+            Online = OnlineState.Offline;
         }
 
         public void AddThreat(float amount)
@@ -866,6 +873,7 @@ namespace Game.Combat
             {
                 Online = ShouldBeSuppressed() ? OnlineState.Suppressed : OnlineState.Online;
                 ListNotifyChanged();
+                _mgr.RegisterForAIUpdate(this);
             }
         }
 

Source/Game/Entities/Creature/Creature.cs

@@ -1047,6 +1047,14 @@ namespace Game.Entities
                 && !GetCreatureTemplate().FlagsExtra.HasAnyFlag(CreatureFlagsExtra.NoXpAtKill);
         }
 
+        public override bool IsEngaged()
+        {
+            CreatureAI ai = GetAI();
+            if (ai != null)
+                return ai.IsEngaged();
+            return false;
+        }
+        
         public override void AtEngage(Unit target)
         {
             base.AtEngage(target);
@@ -1353,7 +1361,7 @@ namespace Game.Entities
             CreatureBaseStats stats = Global.ObjectMgr.GetCreatureBaseStats(level, cInfo.UnitClass);
 
             // health
-            float healthmod = _GetHealthMod(rank);
+            float healthmod = GetHealthMod(rank);
 
             uint basehp = (uint)GetMaxHealthByLevel(level);
             uint health = (uint)(basehp * healthmod);
@@ -1416,7 +1424,7 @@ namespace Game.Entities
             }
         }
 
-        float _GetHealthMod(CreatureEliteType Rank)
+        public float GetHealthMod(CreatureEliteType Rank)
         {
             switch (Rank)                                           // define rates for each elite rank
             {
@@ -1567,7 +1575,7 @@ namespace Game.Entities
                 curhealth = m_creatureData.curhealth;
                 if (curhealth != 0)
                 {
-                    curhealth = (uint)(curhealth * _GetHealthMod(GetCreatureTemplate().Rank));
+                    curhealth = (uint)(curhealth * GetHealthMod(GetCreatureTemplate().Rank));
                     if (curhealth < 1)
                         curhealth = 1;
                 }

Source/Game/Entities/Unit/Unit.Combat.cs

@@ -57,8 +57,9 @@ namespace Game.Entities
             RemoveAurasWithInterruptFlags(SpellAuraInterruptFlags.LeavingCombat);
         }
 
-        public virtual void AtEngage(Unit target) { m_isEngaged = true; }
+        public virtual void AtEngage(Unit target) { }
-        public virtual void AtDisengage() { m_isEngaged = false; }
+
+        public virtual void AtDisengage() { }
 
         public void CombatStop(bool includingCast = false, bool mutualPvP = true)
         {
@@ -147,10 +148,10 @@ namespace Game.Entities
 
         public bool CanHaveThreatList() { return m_threatManager.CanHaveThreatList(); }
 
-        // This value can be different from IsInCombat:
+        // This value can be different from IsInCombat, for example:
         // - when a projectile spell is midair against a creature (combat on launch - threat+aggro on impact)
         // - when the creature has no targets left, but the AI has not yet ceased engaged logic
-        public bool IsEngaged() { return m_isEngaged; }
+        public virtual bool IsEngaged() { return IsInCombat(); }
 
         public bool IsEngagedBy(Unit who) { return CanHaveThreatList() ? IsThreatenedBy(who) : IsInCombatWith(who); }
 
@@ -230,7 +231,6 @@ namespace Game.Entities
                 minion.StopAttackFaction(factionId);
         }
 
-
         public void HandleProcExtraAttackFor(Unit victim)
         {
             while (ExtraAttacks != 0)

Source/Game/Entities/Unit/Unit.Fields.cs

@@ -56,8 +56,6 @@ namespace Game.Entities
         protected uint[] m_attackTimer = new uint[(int)WeaponAttackType.Max];
 
         // Threat+combat management
-        bool m_isEngaged;
-
         CombatManager m_combatManager;
         ThreatManager m_threatManager;
 

Source/Scripts/Pets/Priest.cs

@@ -45,7 +45,7 @@ namespace Scripts.Pets
                     return;
 
                 me.CombatStop(true);
-                me.GetThreatManager().NotifyDisengaged();
+                EngagementOver();
                 me.ResetPlayerDamageReq();
             }
         }