fix(Core\OpCode): HandleFarSightOpcode (#9965)

* Change TO ThreadUNSAFE

This will process the far sight packet as a is not thread-safe - process it in World::UpdateSessions() compared to the former packet is thread-safe - process it in Map::Update().
This matches up with tc in everything we have with the HandleFarSightOpcode.

* Further Adjustments

* Move to Debug Loggin

TC has it as move to Debug Logging. Stating its a weird opcode handling issue which is not really known why.

src/server/game/Entities/Player/Player.cpp

@@ -12385,13 +12385,6 @@ void Player::SetViewpoint(WorldObject* target, bool apply)
 {
     if (apply)
     {
-        // target must be in world
-        if (!target->IsInWorld())
-            return;
-
-        if (!IsInWorld() || IsDuringRemoveFromWorld())
-            return;
-
         LOG_DEBUG("maps", "Player::CreateViewpoint: Player %s create seer %u (TypeId: %u).", GetName().c_str(), target->GetEntry(), target->GetTypeId());
 
         if (!AddGuidValue(PLAYER_FARSIGHT, target->GetGUID()))
@@ -12405,6 +12398,7 @@ void Player::SetViewpoint(WorldObject* target, bool apply)
 
         if (target->isType(TYPEMASK_UNIT) && !GetVehicle())
             ((Unit*)target)->AddPlayerToVision(this);
+        SetSeer(target);
     }
     else
     {
@@ -12413,15 +12407,18 @@ void Player::SetViewpoint(WorldObject* target, bool apply)
 
         LOG_DEBUG("maps", "Player::CreateViewpoint: Player %s remove seer", GetName().c_str());
 
-        if (target->isType(TYPEMASK_UNIT) && !GetVehicle())
-            ((Unit*)target)->RemovePlayerFromVision(this);
-
         if (!RemoveGuidValue(PLAYER_FARSIGHT, target->GetGUID()))
         {
             LOG_FATAL("entities.player", "Player::CreateViewpoint: Player %s cannot remove current viewpoint!", GetName().c_str());
             return;
         }
 
+        if (target->isType(TYPEMASK_UNIT) && !GetVehicle())
+            static_cast<Unit*>(target)->RemovePlayerFromVision(this);
+
+        // must immediately set seer back otherwise may crash
+        SetSeer(this);
+
         //WorldPacket data(SMSG_CLEAR_FAR_SIGHT_IMMEDIATE, 0);
         //GetSession()->SendPacket(&data);
     }

src/server/game/Entities/Unit/Unit.cpp

@@ -351,19 +351,6 @@ Unit::~Unit()
     ASSERT(!m_attacking);
     ASSERT(m_attackers.empty());
 
-    // pussywizard: clear m_sharedVision along with back references
-    if (!m_sharedVision.empty())
-    {
-        LOG_INFO("misc", "Unit::~Unit (B1)");
-        do
-        {
-            LOG_INFO("misc", "Unit::~Unit (B2)");
-            Player* p = *(m_sharedVision.begin());
-            p->m_isInSharedVisionOf.erase(this);
-            m_sharedVision.erase(p);
-        } while (!m_sharedVision.empty());
-    }
-
     ASSERT(m_Controlled.empty());
     ASSERT(m_appliedAuras.empty());
     ASSERT(m_ownedAuras.empty());
@@ -10624,15 +10611,13 @@ void Unit::AddPlayerToVision(Player* player)
         setActive(true);
         SetWorldObject(true);
     }
-    m_sharedVision.insert(player);
-    player->m_isInSharedVisionOf.insert(this);
+    m_sharedVision.push_back(player);
 }
 
 // only called in Player::SetSeer
 void Unit::RemovePlayerFromVision(Player* player)
 {
-    m_sharedVision.erase(player);
-    player->m_isInSharedVisionOf.erase(this);
+    m_sharedVision.remove(player);
     if (m_sharedVision.empty())
     {
         setActive(false);

src/server/game/Entities/Unit/Unit.h

@@ -1196,7 +1196,7 @@ struct UnitActionBarEntry
     }
 };
 
-typedef std::set<Player*> SharedVisionList;
+typedef std::list<Player*> SharedVisionList;
 
 enum CharmType
 {