Core/Entities: Kick engagement logic upstairs to Unit (from ThreatManager), since all Units with AI need it (not just those with threat list).

Port From (https://github.com/TrinityCore/TrinityCore/commit/35e55f10899712435102764671241b94a2026599)

Source/Game/Chat/Commands/DebugCommands.cs

@@ -934,7 +934,7 @@ namespace Game.Chat
             {
                 if (!mgr.IsThreatListEmpty(true))
                 {
-                    if (mgr.IsEngaged())
+                    if (target.IsEngaged())
                         handler.SendSysMessage($"Threat list of {target.GetName()} ({target.GetGUID()}, SpawnID {(target.IsCreature() ? target.ToCreature().GetSpawnId() : 0)}):");
                     else
                         handler.SendSysMessage($"{target.GetName()} ({target.GetGUID()}, SpawnID {(target.IsCreature() ? target.ToCreature().GetSpawnId() : 0)}) is not engaged, but still has a threat list? Well, here it is:");
@@ -948,13 +948,15 @@ namespace Game.Chat
                     }
                     handler.SendSysMessage("End of threat list.");
                 }
-                else if (!mgr.IsEngaged())
+                else if (!target.IsEngaged())
                     handler.SendSysMessage($"{target.GetName()} ({target.GetGUID()}, SpawnID {(target.IsCreature() ? target.ToCreature().GetSpawnId() : 0)}) is not currently engaged.");
                 else
                     handler.SendSysMessage($"{target.GetName()} ({target.GetGUID()}, SpawnID {(target.IsCreature() ? target.ToCreature().GetSpawnId() : 0)}) seems to be engaged, but does not have a threat list??");
             }
+            else if (target.IsEngaged())
+                handler.SendSysMessage($"{target.GetName()} ({target.GetGUID()}) is currently engaged. (This unit cannot have a threat list.)");
             else
-                handler.SendSysMessage($"{target.GetName()} ({target.GetGUID()}) cannot have a threat list.");
+                handler.SendSysMessage($"{target.GetName()} ({target.GetGUID()}) is not currently engaged. (This unit cannot have a threat list.)");
 
             return true;
         }

Source/Game/Combat/CombatManager.cs

@@ -277,11 +277,15 @@ namespace Game.Combat
             {
                 _owner.AddUnitFlag(UnitFlags.InCombat);
                 _owner.AtEnterCombat();
+                if (!_owner.CanHaveThreatList() && !_owner.IsEngaged())
+                    _owner.AtEngage(GetAnyTarget());
             }
             else
             {
                 _owner.RemoveUnitFlag(UnitFlags.InCombat);
                 _owner.AtExitCombat();
+                if (_owner.IsEngaged() && !(_owner.IsCreature() && _owner.ToCreature().IsAIEnabled()))
+                    _owner.AtDisengage();
             }
 
             Unit master = _owner.GetCharmerOrOwner();

Source/Game/Combat/ThreatManager.cs

@@ -32,7 +32,6 @@ namespace Game.Combat
 
         public Unit _owner;
         bool _ownerCanHaveThreatList;
-        bool _ownerEngaged;
 
         public bool NeedClientUpdate;
         uint _updateTimer;
@@ -82,7 +81,7 @@ namespace Game.Combat
 
         public void Update(uint tdiff)
         {
-            if (!CanHaveThreatList() || !IsEngaged())
+            if (!CanHaveThreatList() || IsThreatListEmpty())
                 return;
 
             if (_updateTimer <= tdiff)
@@ -192,13 +191,6 @@ namespace Game.Combat
             }
         }
 
-        static void SaveCreatureHomePositionIfNeed(Creature c)
-        {
-            MovementGeneratorType movetype = c.GetMotionMaster().GetCurrentMovementGeneratorType();
-            if (movetype == MovementGeneratorType.Waypoint || movetype == MovementGeneratorType.Point || (c.IsAIEnabled() && c.GetAI().IsEscorted()))
-                c.SetHomePosition(c.GetPosition());
-        }
-
         public void AddThreat(Unit target, float amount, SpellInfo spell = null, bool ignoreModifiers = false, bool ignoreRedirects = false)
         {
             // step 1: we can shortcut if the spell has one of the NO_THREAT attrs set - nothing will happen
@@ -317,20 +309,10 @@ namespace Game.Combat
             if (newRefe.IsOnline()) // ...and if the ref is online it also gets the threat it should have
                 newRefe.AddThreat(amount);
 
-            if (!_ownerEngaged)
+            if (!_owner.IsEngaged())
             {
-                Creature cOwner = _owner.ToCreature(); // if we got here the owner can have a threat list, and must be a creature!
+                _owner.AtEngage(target);
-                _ownerEngaged = true;
-
                 UpdateVictim();
-                SaveCreatureHomePositionIfNeed(cOwner);
-                CreatureAI ownerAI = cOwner.GetAI();
-                if (ownerAI != null)
-                    ownerAI.JustEngagedWith(target);
-
-                CreatureGroup formation = cOwner.GetFormation();
-                if (formation != null)
-                    formation.MemberEngagingTarget(cOwner, target);
             }
         }
 
@@ -407,14 +389,17 @@ namespace Game.Combat
 
         public void ClearAllThreat()
         {
-            _ownerEngaged = false;
+            if (!_myThreatListEntries.Empty())
-            if (_myThreatListEntries.Empty())
+            {
-                return;
+                SendClearAllThreatToClients();
-
+                do
-            SendClearAllThreatToClients();
+                    _myThreatListEntries.FirstOrDefault().Value.UnregisterAndFree();
-            do
+                while (!_myThreatListEntries.Empty());
-                _myThreatListEntries.First().Value.UnregisterAndFree();
+            }
-            while (!_myThreatListEntries.Empty());
+            // 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)
@@ -783,8 +768,6 @@ namespace Game.Combat
         // identical to ThreatManager::CanHaveThreatList(GetOwner())
         public bool CanHaveThreatList() { return _ownerCanHaveThreatList; }
 
-        public bool IsEngaged() { return _ownerEngaged; }
-
         public int GetThreatListSize() { return _sortedThreatList.Count; }
 
         // fastest of the three threat list getters - gets the threat list in "arbitrary" order

Source/Game/Entities/Creature/Creature.cs

@@ -1042,9 +1042,9 @@ namespace Game.Entities
                 && !GetCreatureTemplate().FlagsExtra.HasAnyFlag(CreatureFlagsExtra.NoXpAtKill);
         }
 
-        public override void AtEnterCombat()
+        public override void AtEngage(Unit target)
         {
-            base.AtEnterCombat();
+            base.AtEngage(target);
 
             if (!GetCreatureTemplate().TypeFlags.HasAnyFlag(CreatureTypeFlags.MountedCombatAllowed))
                 Dismount();
@@ -1055,11 +1055,23 @@ namespace Game.Entities
                 UpdateSpeed(UnitMoveType.Swim);
                 UpdateSpeed(UnitMoveType.Flight);
             }
+
+            MovementGeneratorType movetype = GetMotionMaster().GetCurrentMovementGeneratorType();
+            if (movetype == MovementGeneratorType.Waypoint || movetype == MovementGeneratorType.Point || (IsAIEnabled() && GetAI().IsEscorted()))
+                SetHomePosition(GetPosition());
+
+            CreatureAI ai = GetAI();
+            if (ai != null)
+                ai.JustEngagedWith(target);
+
+            CreatureGroup formation = GetFormation();
+            if (formation != null)
+                formation.MemberEngagingTarget(this, target);
         }
 
-        public override void AtExitCombat()
+        public override void AtDisengage()
         {
-            base.AtExitCombat();
+            base.AtDisengage();
 
             ClearUnitState(UnitState.AttackPlayer);
             if (HasDynamicFlag(UnitDynFlags.Tapped))

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

@@ -57,6 +57,9 @@ namespace Game.Entities
             RemoveAurasWithInterruptFlags(SpellAuraInterruptFlags.LeavingCombat);
         }
 
+        public virtual void AtEngage(Unit target) { m_isEngaged = true; }
+        public virtual void AtDisengage() { m_isEngaged = false; }
+
         public void CombatStop(bool includingCast = false, bool mutualPvP = true)
         {
             if (includingCast && IsNonMeleeSpellCast(false))
@@ -144,10 +147,10 @@ namespace Game.Entities
 
         public bool CanHaveThreatList() { return m_threatManager.CanHaveThreatList(); }
 
-        // For NPCs with threat list: Whether there are any enemies on our threat list
+        // This value can be different from IsInCombat:
-        // For other units: Whether we're in combat
+        // - when a projectile spell is midair against a creature (combat on launch - threat+aggro on impact)
-        // This value is different from IsInCombat when a projectile spell is midair (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 CanHaveThreatList() ? m_threatManager.IsEngaged() : IsInCombat(); }
+        public bool IsEngaged() { return m_isEngaged; }
 
         public bool IsEngagedBy(Unit who) { return CanHaveThreatList() ? IsThreatenedBy(who) : IsInCombatWith(who); }
 

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

@@ -54,6 +54,9 @@ namespace Game.Entities
         internal float[] m_modAttackSpeedPct = new float[(int)WeaponAttackType.Max];
         protected uint[] m_attackTimer = new uint[(int)WeaponAttackType.Max];
 
+        // Threat+combat management
+        bool m_isEngaged;
+
         CombatManager m_combatManager;
         ThreatManager m_threatManager;