Core/AI: Finally move the "is creature engaged" flag to be a property of the creature AI, where it honestly always belonged. Fixes #17981 and #23602 for real this time.

(cherry picked from commit 0e7c66cb4c7ff7d44e232d0b50703a48605ffd24)

9 files changed, 73 insertions, 23 deletions

diff --git a/src/server/game/AI/CoreAI/GuardAI.cpp b/src/server/game/AI/CoreAI/GuardAI.cpp
index 214c8df86f7..aa6ea0e93c4 100644
--- a/src/server/game/AI/CoreAI/GuardAI.cpp
+++ b/src/server/game/AI/CoreAI/GuardAI.cpp
@@ -52,7 +52,7 @@ void GuardAI::EnterEvadeMode(EvadeReason /*why*/)
     {
         me->GetMotionMaster()->MoveIdle();
         me->CombatStop(true);
-        me->GetThreatManager().NotifyDisengaged();
+        EngagementOver();
         return;
     }
 
@@ -60,7 +60,7 @@ void GuardAI::EnterEvadeMode(EvadeReason /*why*/)
 
     me->RemoveAllAuras();
     me->CombatStop(true);
-    me->GetThreatManager().NotifyDisengaged();
+    EngagementOver();
 
     me->GetMotionMaster()->MoveTargetedHome();
 }
diff --git a/src/server/game/AI/CoreAI/PassiveAI.h b/src/server/game/AI/CoreAI/PassiveAI.h
index 582fb737d41..039a5293036 100644
--- a/src/server/game/AI/CoreAI/PassiveAI.h
+++ b/src/server/game/AI/CoreAI/PassiveAI.h
@@ -39,6 +39,9 @@ class TC_GAME_API PossessedAI : public CreatureAI
 
         void MoveInLineOfSight(Unit*) override { }
         void AttackStart(Unit* target) override;
+        void JustEnteredCombat(Unit* who) override { EngagementStart(who); }
+        void JustExitedCombat() override { EngagementOver(); }
+        void JustStartedThreateningMe(Unit*) override { }
         void UpdateAI(uint32) override;
         void EnterEvadeMode(EvadeReason /*why*/) override { }
 
@@ -55,6 +58,8 @@ class TC_GAME_API NullCreatureAI : public CreatureAI
 
         void MoveInLineOfSight(Unit*) override { }
         void AttackStart(Unit*) override { }
+        void JustStartedThreateningMe(Unit*) override { }
+        void JustEnteredCombat(Unit*) override { }
         void UpdateAI(uint32) override { }
         void JustAppeared() override { }
         void EnterEvadeMode(EvadeReason /*why*/) override { }
diff --git a/src/server/game/AI/CoreAI/TotemAI.cpp b/src/server/game/AI/CoreAI/TotemAI.cpp
index 48940a1412b..64741e5993a 100644
--- a/src/server/game/AI/CoreAI/TotemAI.cpp
+++ b/src/server/game/AI/CoreAI/TotemAI.cpp
@@ -33,16 +33,9 @@ int32 TotemAI::Permissible(Creature const* creature)
     return PERMIT_BASE_NO;
 }
 
-TotemAI::TotemAI(Creature* creature, uint32 scriptId) : CreatureAI(creature, scriptId), _victimGUID()
+TotemAI::TotemAI(Creature* creature, uint32 scriptId) : NullCreatureAI(creature, scriptId), _victimGUID()
 {
-    ASSERT(creature->IsTotem(), "TotemAI: AI assigned to a no-totem creature (%s)!", creature->GetGUID().ToString().c_str());
-}
-
-void TotemAI::MoveInLineOfSight(Unit* /*who*/) { }
-
-void TotemAI::EnterEvadeMode(EvadeReason /*why*/)
-{
-    me->CombatStop(true);
+    ASSERT(creature->IsTotem(), "TotemAI: AI assigned to a non-totem creature (%s)!", creature->GetGUID().ToString().c_str());
 }
 
 void TotemAI::UpdateAI(uint32 /*diff*/)
diff --git a/src/server/game/AI/CoreAI/TotemAI.h b/src/server/game/AI/CoreAI/TotemAI.h
index dcc14e963ee..80f387f6a22 100644
--- a/src/server/game/AI/CoreAI/TotemAI.h
+++ b/src/server/game/AI/CoreAI/TotemAI.h
@@ -19,20 +19,18 @@
 #define TRINITY_TOTEMAI_H
 
 #include "CreatureAI.h"
+#include "PassiveAI.h"
 #include "Timer.h"
 
 class Creature;
 class Totem;
 
-class TC_GAME_API TotemAI : public CreatureAI
+class TC_GAME_API TotemAI : public NullCreatureAI
 {
     public:
         explicit TotemAI(Creature* creature, uint32 scriptId = {});
 
-        void MoveInLineOfSight(Unit* who) override;
         void AttackStart(Unit* victim) override;
-        void JustAppeared() override { }
-        void EnterEvadeMode(EvadeReason /*why*/) override;
 
         void UpdateAI(uint32 diff) override;
         static int32 Permissible(Creature const* creature);
diff --git a/src/server/game/AI/CoreAI/UnitAI.cpp b/src/server/game/AI/CoreAI/UnitAI.cpp
index df37aa94f03..642ac34a675 100644
--- a/src/server/game/AI/CoreAI/UnitAI.cpp
+++ b/src/server/game/AI/CoreAI/UnitAI.cpp
@@ -318,7 +318,7 @@ std::string UnitAI::GetDebugInfo() const
 }
 
 DefaultTargetSelector::DefaultTargetSelector(Unit const* unit, float dist, bool playerOnly, bool withTank, int32 aura)
-    : _me(unit), _dist(dist), _playerOnly(playerOnly), _exception(!withTank ? _me->GetThreatManager().GetCurrentVictim() : nullptr), _aura(aura)
+    : _me(unit), _dist(dist), _playerOnly(playerOnly), _exception(!withTank ? unit->GetThreatManager().GetLastVictim() : nullptr), _aura(aura)
 {
 }
 
diff --git a/src/server/game/AI/CreatureAI.cpp b/src/server/game/AI/CreatureAI.cpp
index e1d53238c89..7d617a9c384 100644
--- a/src/server/game/AI/CreatureAI.cpp
+++ b/src/server/game/AI/CreatureAI.cpp
@@ -43,7 +43,7 @@ AISpellInfoType* GetAISpellInfo(uint32 spellId, Difficulty difficulty)
 
 CreatureAI::CreatureAI(Creature* creature, uint32 scriptId)
     : UnitAI(creature), me(creature), _boundary(nullptr),
-      _negateBoundary(false), _scriptId(scriptId ? scriptId : creature->GetScriptId()), _moveInLOSLocked(false)
+      _negateBoundary(false), _scriptId(scriptId ? scriptId : creature->GetScriptId()), _isEngaged(false), _moveInLOSLocked(false)
 {
     ASSERT(_scriptId, "A CreatureAI was initialized with an invalid scriptId!");
 }
@@ -207,6 +207,12 @@ void CreatureAI::JustAppeared()
     }
 }
 
+void CreatureAI::JustEnteredCombat(Unit* who)
+{
+    if (!IsEngaged() && !me->CanHaveThreatList())
+        EngagementStart(who);
+}
+
 void CreatureAI::EnterEvadeMode(EvadeReason why)
 {
     if (!_EnterEvadeMode(why))
@@ -235,7 +241,7 @@ void CreatureAI::EnterEvadeMode(EvadeReason why)
 
 bool CreatureAI::UpdateVictim()
 {
-    if (!me->IsEngaged())
+    if (!IsEngaged())
         return false;
 
     if (!me->HasReactState(REACT_PASSIVE))
@@ -257,22 +263,52 @@ bool CreatureAI::UpdateVictim()
     return true;
 }
 
+void CreatureAI::EngagementStart(Unit* who)
+{
+    if (_isEngaged)
+    {
+        TC_LOG_ERROR("scripts.ai", "CreatureAI::EngagementStart called even though creature is already engaged. Creature debug info:\n%s", me->GetDebugInfo().c_str());
+        return;
+    }
+    _isEngaged = true;
+
+    me->AtEngage(who);
+}
+
+void CreatureAI::EngagementOver()
+{
+    if (!_isEngaged)
+    {
+        TC_LOG_ERROR("scripts.ai", "CreatureAI::EngagementOver called even though creature is not currently engaged. Creature debug info:\n%s", me->GetDebugInfo().c_str());
+        return;
+    }
+    _isEngaged = false;
+
+    me->AtDisengage();
+}
+
 bool CreatureAI::_EnterEvadeMode(EvadeReason /*why*/)
 {
+    if (me->IsInEvadeMode())
+        return false;
+
     if (!me->IsAlive())
+    {
+        EngagementOver();
         return false;
+    }
 
     me->RemoveAurasOnEvade();
 
     me->CombatStop(true);
-    me->GetThreatManager().NotifyDisengaged();
     me->SetLootRecipient(nullptr);
     me->ResetPlayerDamageReq();
     me->SetLastDamagedTime(0);
     me->SetCannotReachTarget(false);
     me->DoNotReacquireTarget();
+    EngagementOver();
 
-    return !me->IsInEvadeMode();
+    return true;
 }
 
 Optional<QuestGiverStatus> CreatureAI::GetDialogStatus(Player* /*player*/)
diff --git a/src/server/game/AI/CreatureAI.h b/src/server/game/AI/CreatureAI.h
index 165b905803e..eef2cc0bd6b 100644
--- a/src/server/game/AI/CreatureAI.h
+++ b/src/server/game/AI/CreatureAI.h
@@ -84,6 +84,8 @@ class TC_GAME_API CreatureAI : public UnitAI
         // Gets the id of the AI (script id)
         uint32 GetId() const { return _scriptId; }
 
+        bool IsEngaged() const { return _isEngaged; }
+
         void Talk(uint8 id, WorldObject const* whisperTarget = nullptr);
 
         /// == Reactions At =================================
@@ -97,11 +99,17 @@ class TC_GAME_API CreatureAI : public UnitAI
         // Called for reaction at stopping attack at no attackers or targets
         virtual void EnterEvadeMode(EvadeReason why = EVADE_REASON_OTHER);
 
+        // Called for reaction whenever we start being in combat (overridden from base UnitAI)
+        void JustEnteredCombat(Unit* /*who*/) override;
+
+        // Called for reaction whenever a new non-offline unit is added to the threat list
+        virtual void JustStartedThreateningMe(Unit* who) { if (!IsEngaged()) EngagementStart(who); }
+
         // Called for reaction when initially engaged - this will always happen _after_ JustEnteredCombat
         virtual void JustEngagedWith(Unit* /*who*/) { }
 
         // Called when the creature is killed
-        virtual void JustDied(Unit* /*killer*/) { }
+        virtual void JustDied(Unit* /*killer*/) { if (IsEngaged()) EngagementOver(); }
 
         // Called when the creature kills a unit
         virtual void KilledUnit(Unit* /*victim*/) { }
@@ -227,6 +235,8 @@ class TC_GAME_API CreatureAI : public UnitAI
 
         // intended for encounter design/debugging. do not use for other purposes. expensive.
         int32 VisualizeBoundary(uint32 duration, Unit* owner = nullptr, bool fill = false) const;
+
+        // boundary system methods
         virtual bool CheckInRoom();
         CreatureBoundary const* GetBoundary() const { return _boundary; }
         void SetBoundary(CreatureBoundary const* boundary, bool negativeBoundaries = false);
@@ -235,6 +245,8 @@ class TC_GAME_API CreatureAI : public UnitAI
         bool IsInBoundary(Position const* who = nullptr) const;
 
     protected:
+        void EngagementStart(Unit* who);
+        void EngagementOver();
         virtual void MoveInLineOfSight(Unit* /*who*/);
 
         bool _EnterEvadeMode(EvadeReason why = EVADE_REASON_OTHER);
@@ -246,6 +258,7 @@ class TC_GAME_API CreatureAI : public UnitAI
         void OnOwnerCombatInteraction(Unit* target);
 
         uint32 const _scriptId;
+        bool _isEngaged;
         bool _moveInLOSLocked;
 };
 
diff --git a/src/server/game/AI/ScriptedAI/ScriptedEscortAI.cpp b/src/server/game/AI/ScriptedAI/ScriptedEscortAI.cpp
index 91efe5d5312..63592dd30ba 100644
--- a/src/server/game/AI/ScriptedAI/ScriptedEscortAI.cpp
+++ b/src/server/game/AI/ScriptedAI/ScriptedEscortAI.cpp
@@ -94,8 +94,9 @@ void EscortAI::EnterEvadeMode(EvadeReason /*why*/)
 {
     me->RemoveAllAuras();
     me->CombatStop(true);
-    me->GetThreatManager().NotifyDisengaged();
     me->SetLootRecipient(nullptr);
+    
+    EngagementOver();
 
     if (HasEscortState(STATE_ESCORT_ESCORTING))
     {
diff --git a/src/server/game/AI/ScriptedAI/ScriptedFollowerAI.cpp b/src/server/game/AI/ScriptedAI/ScriptedFollowerAI.cpp
index 669022d8420..d8f0d972cd1 100644
--- a/src/server/game/AI/ScriptedAI/ScriptedFollowerAI.cpp
+++ b/src/server/game/AI/ScriptedAI/ScriptedFollowerAI.cpp
@@ -103,14 +103,18 @@ void FollowerAI::JustAppeared()
 void FollowerAI::EnterEvadeMode(EvadeReason /*why*/)
 {
     if (!me->IsAlive())
+    {
+        EngagementOver();
         return;
+    }
 
     me->RemoveAllAuras();
     me->CombatStop(true);
-    me->GetThreatManager().NotifyDisengaged();
     me->SetLootRecipient(nullptr);
     me->SetCannotReachTarget(false);
     me->DoNotReacquireTarget();
+    
+    EngagementOver();
 
     if (HasFollowState(STATE_FOLLOW_INPROGRESS))
     {