Core/Creatures: Implemented UNIT_NPC_FLAG_GOSSIP as viewer dependent and update npcflags on quest changes

Port From (https://github.com/TrinityCore/TrinityCore/commit/dd15d763cc0529afc9b7f077817645d875608626)

Source/Game/Entities/Player/Player.Quest.cs

@@ -841,6 +841,8 @@ namespace Game.Entities
 
             Global.ScriptMgr.OnQuestStatusChange(this, questId);
             Global.ScriptMgr.OnQuestStatusChange(this, quest, oldStatus, questStatusData.Status);
+
+            UpdateNearbyCreatureNpcFlags();
         }
 
         public void CompleteQuest(uint quest_id)
@@ -1228,6 +1230,8 @@ namespace Game.Entities
             if (quest.HasFlag(QuestFlags.UpdatePhaseshift))
                 updateVisibility = PhasingHandler.OnConditionChange(this, false);
 
+            UpdateNearbyCreatureNpcFlags();
+
             //lets remove flag for delayed teleports
             SetCanDelayTeleport(false);
 
@@ -1258,6 +1262,8 @@ namespace Game.Entities
 
             if (updateVisibility)
                 UpdateObjectVisibility();
+
+            UpdateNearbyCreatureNpcFlags();
         }
 
         public void SetRewardedQuest(uint questId)
@@ -1910,6 +1916,8 @@ namespace Game.Entities
                 Global.ScriptMgr.OnQuestStatusChange(this, quest, oldStatus, status);
             }
 
+            UpdateNearbyCreatureNpcFlags();
+
             if (update)
                 SendQuestUpdate(questId);
         }
@@ -2184,6 +2192,8 @@ namespace Game.Entities
 
             if (updateVisibility)
                 UpdateObjectVisibility();
+
+            UpdateNearbyCreatureNpcFlags();
         }
 
         public void DespawnPersonalSummonsForQuest(uint questId)
@@ -2705,6 +2715,8 @@ namespace Game.Entities
             if (updatePhaseShift)
                 PhasingHandler.OnConditionChange(this);
 
+            UpdateNearbyCreatureNpcFlags();
+
             if (updateZoneAuras)
             {
                 UpdateZoneDependentAuras(GetZoneId());
@@ -2753,6 +2765,39 @@ namespace Game.Entities
             return false;
         }
 
+        public bool CanSeeGossipOn(Creature creature)
+        {
+            if (creature.HasNpcFlag(NPCFlags.Gossip))
+            {
+                if (GetGossipMenuForSource(creature) != 0)
+                    return true;
+            }
+
+            // for cases with questgiver/ender without gossip menus
+            if (creature.HasNpcFlag(NPCFlags.QuestGiver))
+            {
+                QuestRelationResult objectQIR = Global.ObjectMgr.GetCreatureQuestInvolvedRelations(creature.GetEntry());
+                foreach (uint quest_id in objectQIR)
+                {
+                    QuestStatus status = GetQuestStatus(quest_id);
+                    if (status == QuestStatus.Complete || status == QuestStatus.Incomplete)
+                        return true;
+                }
+
+                QuestRelationResult objectQR = Global.ObjectMgr.GetCreatureQuestRelations(creature.GetEntry());
+                foreach (uint quest_id in objectQR)
+                {
+                    Quest quest = Global.ObjectMgr.GetQuestTemplate(quest_id);
+                    if (quest == null)
+                        continue;
+
+                    if (CanTakeQuest(quest, false))
+                        return true;
+                }
+            }
+            return false;
+        }
+
         QuestObjective GetQuestObjectiveForItem(uint itemId, bool onlyIncomplete)
         {
             QuestObjective findObjectiveForItem(int tempItemId)