com.unity.netcode.gameobjects/Runtime/Spawning/NetworkSpawnManager.cs

using System;
using System.Collections.Generic;
using System.Linq;
using Unity.Collections;
using UnityEngine;

namespace Unity.Netcode
{
    /// <summary>
    /// Class that handles object spawning
    /// </summary>
    public class NetworkSpawnManager
    {
        /// <summary>
        /// The currently spawned objects
        /// </summary>
        public readonly Dictionary<ulong, NetworkObject> SpawnedObjects = new Dictionary<ulong, NetworkObject>();

        /// <summary>
        /// A list of the spawned objects
        /// </summary>
        public readonly HashSet<NetworkObject> SpawnedObjectsList = new HashSet<NetworkObject>();

        /// <summary>
        /// Use to get all NetworkObjects owned by a client
        /// Ownership to Objects Table Format:
        /// [ClientId][NetworkObjectId][NetworkObject]
        /// Server: Keeps track of all clients' ownership
        /// Client: Keeps track of only its ownership
        /// </summary>
        public readonly Dictionary<ulong, Dictionary<ulong, NetworkObject>> OwnershipToObjectsTable = new Dictionary<ulong, Dictionary<ulong, NetworkObject>>();

        /// <summary>
        /// Object to Ownership Table:
        /// [NetworkObjectId][ClientId]
        /// Used internally to find the client Id that currently owns
        /// the NetworkObject
        /// </summary>
        private Dictionary<ulong, ulong> m_ObjectToOwnershipTable = new Dictionary<ulong, ulong>();

        /// <summary>
        /// Used to update a NetworkObject's ownership
        /// </summary>
        internal void UpdateOwnershipTable(NetworkObject networkObject, ulong newOwner, bool isRemoving = false)
        {
            var previousOwner = newOwner;

            // Use internal lookup table to see if the NetworkObject has a previous owner
            if (m_ObjectToOwnershipTable.ContainsKey(networkObject.NetworkObjectId))
            {
                // Keep track of the previous owner's ClientId
                previousOwner = m_ObjectToOwnershipTable[networkObject.NetworkObjectId];

                // We are either despawning (remove) or changing ownership (assign)
                if (isRemoving)
                {
                    m_ObjectToOwnershipTable.Remove(networkObject.NetworkObjectId);
                }
                else
                {
                    m_ObjectToOwnershipTable[networkObject.NetworkObjectId] = newOwner;
                }
            }
            else
            {
                // Otherwise, just add a new lookup entry
                m_ObjectToOwnershipTable.Add(networkObject.NetworkObjectId, newOwner);
            }

            // Check to see if we had a previous owner
            if (previousOwner != newOwner && OwnershipToObjectsTable.ContainsKey(previousOwner))
            {
                // Before updating the previous owner, assure this entry exists
                if (OwnershipToObjectsTable[previousOwner].ContainsKey(networkObject.NetworkObjectId))
                {
                    // Remove the previous owner's entry
                    OwnershipToObjectsTable[previousOwner].Remove(networkObject.NetworkObjectId);

                    // Server or Host alway invokes the lost ownership notification locally
                    if (NetworkManager.IsServer)
                    {
                        networkObject.InvokeBehaviourOnLostOwnership();
                    }

                    // If we are removing the entry (i.e. despawning or client lost ownership)
                    if (isRemoving)
                    {
                        return;
                    }
                }
                else
                {
                    // Really, as long as UpdateOwnershipTable is invoked when ownership is gained or lost this should never happen
                    throw new Exception($"Client-ID {previousOwner} had a partial {nameof(m_ObjectToOwnershipTable)} entry! Potentially corrupted {nameof(OwnershipToObjectsTable)}?");
                }
            }

            // If the owner doesn't have an entry then create one
            if (!OwnershipToObjectsTable.ContainsKey(newOwner))
            {
                OwnershipToObjectsTable.Add(newOwner, new Dictionary<ulong, NetworkObject>());
            }

            // Sanity check to make sure we don't already have this entry (we shouldn't)
            if (!OwnershipToObjectsTable[newOwner].ContainsKey(networkObject.NetworkObjectId))
            {
                // Add the new ownership entry
                OwnershipToObjectsTable[newOwner].Add(networkObject.NetworkObjectId, networkObject);

                // Server or Host always invokes the gained ownership notification locally
                if (NetworkManager.IsServer)
                {
                    networkObject.InvokeBehaviourOnGainedOwnership();
                }
            }
            else if (isRemoving)
            {
                OwnershipToObjectsTable[previousOwner].Remove(networkObject.NetworkObjectId);
            }
            else if (NetworkManager.LogLevel == LogLevel.Developer)
            {
                NetworkLog.LogWarning($"Setting ownership twice? Client-ID {previousOwner} already owns NetworkObject ID {networkObject.NetworkObjectId}!");
            }
        }

        /// <summary>
        /// Returns a list of all NetworkObjects that belong to a client.
        /// </summary>
        /// <param name="clientId">the client's id  <see cref="NetworkManager.LocalClientId"/></param>
        public List<NetworkObject> GetClientOwnedObjects(ulong clientId)
        {
            if (!OwnershipToObjectsTable.ContainsKey(clientId))
            {
                OwnershipToObjectsTable.Add(clientId, new Dictionary<ulong, NetworkObject>());
            }
            return OwnershipToObjectsTable[clientId].Values.ToList();
        }


        private struct TriggerData
        {
            public FastBufferReader Reader;
            public MessageHeader Header;
            public ulong SenderId;
            public float Timestamp;
            public int SerializedHeaderSize;
        }
        private struct TriggerInfo
        {
            public float Expiry;
            public NativeList<TriggerData> TriggerData;
        }

        private readonly Dictionary<ulong, TriggerInfo> m_Triggers = new Dictionary<ulong, TriggerInfo>();

        /// <summary>
        /// Gets the NetworkManager associated with this SpawnManager.
        /// </summary>
        public NetworkManager NetworkManager { get; }

        internal NetworkSpawnManager(NetworkManager networkManager)
        {
            NetworkManager = networkManager;
        }

        internal readonly Queue<ReleasedNetworkId> ReleasedNetworkObjectIds = new Queue<ReleasedNetworkId>();
        private ulong m_NetworkObjectIdCounter;

        // A list of target ClientId, use when sending despawn commands. Kept as a member to reduce memory allocations
        private List<ulong> m_TargetClientIds = new List<ulong>();

        internal ulong GetNetworkObjectId()
        {
            if (ReleasedNetworkObjectIds.Count > 0 && NetworkManager.NetworkConfig.RecycleNetworkIds && (Time.unscaledTime - ReleasedNetworkObjectIds.Peek().ReleaseTime) >= NetworkManager.NetworkConfig.NetworkIdRecycleDelay)
            {
                return ReleasedNetworkObjectIds.Dequeue().NetworkId;
            }

            m_NetworkObjectIdCounter++;

            return m_NetworkObjectIdCounter;
        }

        /// <summary>
        /// Returns the local player object or null if one does not exist
        /// </summary>
        /// <returns>The local player object or null if one does not exist</returns>
        public NetworkObject GetLocalPlayerObject()
        {
            return GetPlayerNetworkObject(NetworkManager.LocalClientId);
        }

        /// <summary>
        /// Returns the player object with a given clientId or null if one does not exist. This is only valid server side.
        /// </summary>
        /// <returns>The player object with a given clientId or null if one does not exist</returns>
        public NetworkObject GetPlayerNetworkObject(ulong clientId)
        {
            if (!NetworkManager.IsServer && NetworkManager.LocalClientId != clientId)
            {
                throw new NotServerException("Only the server can find player objects from other clients.");
            }

            if (TryGetNetworkClient(clientId, out NetworkClient networkClient))
            {
                return networkClient.PlayerObject;
            }

            return null;
        }

        /// <summary>
        /// Defers processing of a message until the moment a specific networkObjectId is spawned.
        /// This is to handle situations where an RPC or other object-specific message arrives before the spawn does,
        /// either due to it being requested in OnNetworkSpawn before the spawn call has been executed
        ///
        /// There is a one second maximum lifetime of triggers to avoid memory leaks. After one second has passed
        /// without the requested object ID being spawned, the triggers for it are automatically deleted.
        /// </summary>
        internal unsafe void TriggerOnSpawn(ulong networkObjectId, FastBufferReader reader, ref NetworkContext context)
        {
            if (!m_Triggers.ContainsKey(networkObjectId))
            {
                m_Triggers[networkObjectId] = new TriggerInfo
                {
                    Expiry = Time.realtimeSinceStartup + 1,
                    TriggerData = new NativeList<TriggerData>(Allocator.Persistent)
                };
            }

            m_Triggers[networkObjectId].TriggerData.Add(new TriggerData
            {
                Reader = new FastBufferReader(reader.GetUnsafePtr(), Allocator.Persistent, reader.Length),
                Header = context.Header,
                Timestamp = context.Timestamp,
                SenderId = context.SenderId,
                SerializedHeaderSize = context.SerializedHeaderSize
            });
        }

        /// <summary>
        /// Cleans up any trigger that's existed for more than a second.
        /// These triggers were probably for situations where a request was received after a despawn rather than before a spawn.
        /// </summary>
        internal unsafe void CleanupStaleTriggers()
        {
            ulong* staleKeys = stackalloc ulong[m_Triggers.Count()];
            int index = 0;
            foreach (var kvp in m_Triggers)
            {
                if (kvp.Value.Expiry < Time.realtimeSinceStartup)
                {

                    staleKeys[index++] = kvp.Key;
                    if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
                    {
                        NetworkLog.LogWarning($"Deferred messages were received for {nameof(NetworkObject)} #{kvp.Key}, but it did not spawn within 1 second.");
                    }

                    foreach (var data in kvp.Value.TriggerData)
                    {
                        data.Reader.Dispose();
                    }

                    kvp.Value.TriggerData.Dispose();
                }
            }

            for (var i = 0; i < index; ++i)
            {
                m_Triggers.Remove(staleKeys[i]);
            }
        }
        /// <summary>
        /// Cleans up any trigger that's existed for more than a second.
        /// These triggers were probably for situations where a request was received after a despawn rather than before a spawn.
        /// </summary>
        internal void CleanupAllTriggers()
        {
            foreach (var kvp in m_Triggers)
            {
                foreach (var data in kvp.Value.TriggerData)
                {
                    data.Reader.Dispose();
                }

                kvp.Value.TriggerData.Dispose();
            }

            m_Triggers.Clear();
        }

        internal void RemoveOwnership(NetworkObject networkObject)
        {
            if (!NetworkManager.IsServer)
            {
                throw new NotServerException("Only the server can change ownership");
            }

            if (!networkObject.IsSpawned)
            {
                throw new SpawnStateException("Object is not spawned");
            }

            // If we made it here then we are the server and if the server is determined to already be the owner
            // then ignore the RemoveOwnership invocation.
            if (networkObject.OwnerClientId == NetworkManager.ServerClientId)
            {
                return;
            }

            // Server removes the entry and takes over ownership before notifying
            UpdateOwnershipTable(networkObject, NetworkManager.ServerClientId, true);

            networkObject.OwnerClientId = NetworkManager.ServerClientId;

            var message = new ChangeOwnershipMessage
            {
                NetworkObjectId = networkObject.NetworkObjectId,
                OwnerClientId = networkObject.OwnerClientId
            };
            var size = NetworkManager.SendMessage(ref message, NetworkDelivery.ReliableSequenced, NetworkManager.ConnectedClientsIds);

            foreach (var client in NetworkManager.ConnectedClients)
            {
                NetworkManager.NetworkMetrics.TrackOwnershipChangeSent(client.Key, networkObject, size);
            }
        }

        /// <summary>
        /// Helper function to get a network client for a clientId from the NetworkManager.
        /// On the server this will check the <see cref="NetworkManager.ConnectedClients"/> list.
        /// On a non-server this will check the <see cref="NetworkManager.LocalClient"/> only.
        /// </summary>
        /// <param name="clientId">The clientId for which to try getting the NetworkClient for.</param>
        /// <param name="networkClient">The found NetworkClient. Null if no client was found.</param>
        /// <returns>True if a NetworkClient with a matching id was found else false.</returns>
        private bool TryGetNetworkClient(ulong clientId, out NetworkClient networkClient)
        {
            if (NetworkManager.IsServer)
            {
                return NetworkManager.ConnectedClients.TryGetValue(clientId, out networkClient);
            }

            if (NetworkManager.LocalClient != null && clientId == NetworkManager.LocalClient.ClientId)
            {
                networkClient = NetworkManager.LocalClient;
                return true;
            }

            networkClient = null;
            return false;
        }

        internal void ChangeOwnership(NetworkObject networkObject, ulong clientId)
        {
            if (!NetworkManager.IsServer)
            {
                throw new NotServerException("Only the server can change ownership");
            }

            if (!networkObject.IsSpawned)
            {
                throw new SpawnStateException("Object is not spawned");
            }

            networkObject.OwnerClientId = clientId;

            // Server adds entries for all client ownership
            UpdateOwnershipTable(networkObject, networkObject.OwnerClientId);

            var message = new ChangeOwnershipMessage
            {
                NetworkObjectId = networkObject.NetworkObjectId,
                OwnerClientId = networkObject.OwnerClientId
            };
            var size = NetworkManager.SendMessage(ref message, NetworkDelivery.ReliableSequenced, NetworkManager.ConnectedClientsIds);

            foreach (var client in NetworkManager.ConnectedClients)
            {
                NetworkManager.NetworkMetrics.TrackOwnershipChangeSent(client.Key, networkObject, size);
            }
        }

        /// <summary>
        /// Should only run on the client
        /// </summary>
        internal NetworkObject CreateLocalNetworkObject(bool isSceneObject, uint globalObjectIdHash, ulong ownerClientId, ulong? parentNetworkId, Vector3? position, Quaternion? rotation, bool isReparented = false)
        {
            NetworkObject parentNetworkObject = null;

            if (parentNetworkId != null && !isReparented)
            {
                if (SpawnedObjects.TryGetValue(parentNetworkId.Value, out NetworkObject networkObject))
                {
                    parentNetworkObject = networkObject;
                }
                else
                {
                    if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
                    {
                        NetworkLog.LogWarning("Cannot find parent. Parent objects always have to be spawned and replicated BEFORE the child");
                    }
                }
            }

            if (!NetworkManager.NetworkConfig.EnableSceneManagement || !isSceneObject)
            {
                // If the prefab hash has a registered INetworkPrefabInstanceHandler derived class
                if (NetworkManager.PrefabHandler.ContainsHandler(globalObjectIdHash))
                {
                    // Let the handler spawn the NetworkObject
                    var networkObject = NetworkManager.PrefabHandler.HandleNetworkPrefabSpawn(globalObjectIdHash, ownerClientId, position.GetValueOrDefault(Vector3.zero), rotation.GetValueOrDefault(Quaternion.identity));

                    networkObject.NetworkManagerOwner = NetworkManager;

                    if (parentNetworkObject != null)
                    {
                        networkObject.transform.SetParent(parentNetworkObject.transform, true);
                    }

                    if (NetworkSceneManager.IsSpawnedObjectsPendingInDontDestroyOnLoad)
                    {
                        UnityEngine.Object.DontDestroyOnLoad(networkObject.gameObject);
                    }

                    return networkObject;
                }
                else
                {
                    // See if there is a valid registered NetworkPrefabOverrideLink associated with the provided prefabHash
                    GameObject networkPrefabReference = null;
                    if (NetworkManager.NetworkConfig.NetworkPrefabOverrideLinks.ContainsKey(globalObjectIdHash))
                    {
                        switch (NetworkManager.NetworkConfig.NetworkPrefabOverrideLinks[globalObjectIdHash].Override)
                        {
                            default:
                            case NetworkPrefabOverride.None:
                                networkPrefabReference = NetworkManager.NetworkConfig.NetworkPrefabOverrideLinks[globalObjectIdHash].Prefab;
                                break;
                            case NetworkPrefabOverride.Hash:
                            case NetworkPrefabOverride.Prefab:
                                networkPrefabReference = NetworkManager.NetworkConfig.NetworkPrefabOverrideLinks[globalObjectIdHash].OverridingTargetPrefab;
                                break;
                        }
                    }

                    // If not, then there is an issue (user possibly didn't register the prefab properly?)
                    if (networkPrefabReference == null)
                    {
                        if (NetworkLog.CurrentLogLevel <= LogLevel.Error)
                        {
                            NetworkLog.LogError($"Failed to create object locally. [{nameof(globalObjectIdHash)}={globalObjectIdHash}]. {nameof(NetworkPrefab)} could not be found. Is the prefab registered with {nameof(NetworkManager)}?");
                        }

                        return null;
                    }

                    // Otherwise, instantiate an instance of the NetworkPrefab linked to the prefabHash
                    var networkObject = ((position == null && rotation == null) ? UnityEngine.Object.Instantiate(networkPrefabReference) : UnityEngine.Object.Instantiate(networkPrefabReference, position.GetValueOrDefault(Vector3.zero), rotation.GetValueOrDefault(Quaternion.identity))).GetComponent<NetworkObject>();

                    networkObject.NetworkManagerOwner = NetworkManager;

                    if (parentNetworkObject != null)
                    {
                        networkObject.transform.SetParent(parentNetworkObject.transform, true);
                    }

                    if (NetworkSceneManager.IsSpawnedObjectsPendingInDontDestroyOnLoad)
                    {
                        UnityEngine.Object.DontDestroyOnLoad(networkObject.gameObject);
                    }

                    return networkObject;
                }
            }
            else
            {
                var networkObject = NetworkManager.SceneManager.GetSceneRelativeInSceneNetworkObject(globalObjectIdHash);

                if (networkObject == null)
                {
                    if (NetworkLog.CurrentLogLevel <= LogLevel.Error)
                    {
                        NetworkLog.LogError($"{nameof(NetworkPrefab)} hash was not found! In-Scene placed {nameof(NetworkObject)} soft synchronization failure for Hash: {globalObjectIdHash}!");
                    }

                    return null;
                }

                if (parentNetworkObject != null)
                {
                    networkObject.transform.SetParent(parentNetworkObject.transform, true);
                }

                return networkObject;
            }
        }

        // Ran on both server and client
        internal void SpawnNetworkObjectLocally(NetworkObject networkObject, ulong networkId, bool sceneObject, bool playerObject, ulong ownerClientId, bool destroyWithScene)
        {
            if (networkObject == null)
            {
                throw new ArgumentNullException(nameof(networkObject), "Cannot spawn null object");
            }

            if (networkObject.IsSpawned)
            {
                throw new SpawnStateException("Object is already spawned");
            }

            if (!sceneObject)
            {
                var networkObjectChildren = networkObject.GetComponentsInChildren<NetworkObject>();
                if (networkObjectChildren.Length > 1)
                {
                    Debug.LogError("Spawning NetworkObjects with nested NetworkObjects is only supported for scene objects. Child NetworkObjects will not be spawned over the network!");
                }
            }

            SpawnNetworkObjectLocallyCommon(networkObject, networkId, sceneObject, playerObject, ownerClientId, destroyWithScene);
        }

        // Ran on both server and client
        internal void SpawnNetworkObjectLocally(NetworkObject networkObject, in NetworkObject.SceneObject sceneObject,
            FastBufferReader variableData, bool destroyWithScene)
        {
            if (networkObject == null)
            {
                throw new ArgumentNullException(nameof(networkObject), "Cannot spawn null object");
            }

            if (networkObject.IsSpawned)
            {
                throw new SpawnStateException("Object is already spawned");
            }

            networkObject.SetNetworkVariableData(variableData);

            SpawnNetworkObjectLocallyCommon(networkObject, sceneObject.Header.NetworkObjectId, sceneObject.Header.IsSceneObject, sceneObject.Header.IsPlayerObject, sceneObject.Header.OwnerClientId, destroyWithScene);
        }

        private void SpawnNetworkObjectLocallyCommon(NetworkObject networkObject, ulong networkId, bool sceneObject, bool playerObject, ulong ownerClientId, bool destroyWithScene)
        {
            if (SpawnedObjects.ContainsKey(networkId))
            {
                Debug.LogWarning($"Trying to spawn {nameof(NetworkObject.NetworkObjectId)} {networkId} that already exists!");
                return;
            }

            // this initialization really should be at the bottom of the function
            networkObject.IsSpawned = true;

            // this initialization really should be at the top of this function. If and when we break the
            //  NetworkVariable dependency on NetworkBehaviour, this otherwise creates problems because
            //  SetNetworkVariableData above calls InitializeVariables, and the 'baked out' data isn't ready there;
            //  the current design banks on getting the network behaviour set and then only reading from it after the
            //  below initialization code. However cowardice compels me to hold off on moving this until that commit
            networkObject.IsSceneObject = sceneObject;
            networkObject.NetworkObjectId = networkId;

            networkObject.DestroyWithScene = sceneObject || destroyWithScene;

            networkObject.OwnerClientId = ownerClientId;

            networkObject.IsPlayerObject = playerObject;

            SpawnedObjects.Add(networkObject.NetworkObjectId, networkObject);
            SpawnedObjectsList.Add(networkObject);

            if (NetworkManager.IsServer)
            {
                if (playerObject)
                {
                    // If there was an already existing player object for this player, then mark it as no longer
                    // a player object.
                    if (NetworkManager.ConnectedClients[ownerClientId].PlayerObject != null)
                    {
                        NetworkManager.ConnectedClients[ownerClientId].PlayerObject.IsPlayerObject = false;
                    }
                    NetworkManager.ConnectedClients[ownerClientId].PlayerObject = networkObject;
                }
            }
            else if (ownerClientId == NetworkManager.LocalClientId)
            {
                if (playerObject)
                {
                    // If there was an already existing player object for this player, then mark it as no longer a player object.
                    if (NetworkManager.LocalClient.PlayerObject != null)
                    {
                        NetworkManager.LocalClient.PlayerObject.IsPlayerObject = false;
                    }
                    NetworkManager.LocalClient.PlayerObject = networkObject;
                }
            }

            if (NetworkManager.IsServer)
            {
                for (int i = 0; i < NetworkManager.ConnectedClientsList.Count; i++)
                {
                    if (networkObject.CheckObjectVisibility == null || networkObject.CheckObjectVisibility(NetworkManager.ConnectedClientsList[i].ClientId))
                    {
                        networkObject.Observers.Add(NetworkManager.ConnectedClientsList[i].ClientId);
                    }
                }
            }

            networkObject.SetCachedParent(networkObject.transform.parent);
            networkObject.ApplyNetworkParenting();
            NetworkObject.CheckOrphanChildren();

            networkObject.InvokeBehaviourNetworkSpawn();

            // This must happen after InvokeBehaviourNetworkSpawn, otherwise ClientRPCs and other messages can be
            // processed before the object is fully spawned. This must be the last thing done in the spawn process.
            if (m_Triggers.ContainsKey(networkId))
            {
                var triggerInfo = m_Triggers[networkId];
                foreach (var trigger in triggerInfo.TriggerData)
                {
                    // Reader will be disposed within HandleMessage
                    NetworkManager.MessagingSystem.HandleMessage(trigger.Header, trigger.Reader, trigger.SenderId, trigger.Timestamp, trigger.SerializedHeaderSize);
                }

                triggerInfo.TriggerData.Dispose();
                m_Triggers.Remove(networkId);
            }

            // propagate the IsSceneObject setting to child NetworkObjects
            var children = networkObject.GetComponentsInChildren<NetworkObject>();
            foreach (var childObject in children)
            {
                childObject.IsSceneObject = sceneObject;
            }
        }

        internal void SendSpawnCallForObject(ulong clientId, NetworkObject networkObject)
        {
            //Currently, if this is called and the clientId (destination) is the server's client Id, this case will be checked
            // within the below Send function.  To avoid unwarranted allocation of a PooledNetworkBuffer placing this check here. [NSS]
            if (NetworkManager.IsServer && clientId == NetworkManager.ServerClientId)
            {
                return;
            }

            var message = new CreateObjectMessage
            {
                ObjectInfo = networkObject.GetMessageSceneObject(clientId)
            };
            var size = NetworkManager.SendMessage(ref message, NetworkDelivery.ReliableFragmentedSequenced, clientId);
            NetworkManager.NetworkMetrics.TrackObjectSpawnSent(clientId, networkObject, size);

            networkObject.MarkVariablesDirty();
        }

        internal ulong? GetSpawnParentId(NetworkObject networkObject)
        {
            NetworkObject parentNetworkObject = null;

            if (!networkObject.AlwaysReplicateAsRoot && networkObject.transform.parent != null)
            {
                parentNetworkObject = networkObject.transform.parent.GetComponent<NetworkObject>();
            }

            if (parentNetworkObject == null)
            {
                return null;
            }

            return parentNetworkObject.NetworkObjectId;
        }

        internal void DespawnObject(NetworkObject networkObject, bool destroyObject = false)
        {
            if (!networkObject.IsSpawned)
            {
                throw new SpawnStateException("Object is not spawned");
            }

            if (!NetworkManager.IsServer)
            {
                throw new NotServerException("Only server can despawn objects");
            }

            OnDespawnObject(networkObject, destroyObject);
        }

        // Makes scene objects ready to be reused
        internal void ServerResetShudownStateForSceneObjects()
        {
            var networkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>().Where((c) => c.IsSceneObject != null && c.IsSceneObject == true);
            foreach (var sobj in networkObjects)
            {
                sobj.IsSpawned = false;
                sobj.DestroyWithScene = false;
                sobj.IsSceneObject = null;
            }
        }

        /// <summary>
        /// Gets called only by NetworkSceneManager.SwitchScene
        /// </summary>
        internal void ServerDestroySpawnedSceneObjects()
        {
            // This Allocation is "OK" for now because this code only executes when a new scene is switched to
            // We need to create a new copy the HashSet of NetworkObjects (SpawnedObjectsList) so we can remove
            // objects from the HashSet (SpawnedObjectsList) without causing a list has been modified exception to occur.
            var spawnedObjects = SpawnedObjectsList.ToList();

            foreach (var sobj in spawnedObjects)
            {
                if (sobj.IsSceneObject != null && sobj.IsSceneObject.Value && sobj.DestroyWithScene && sobj.gameObject.scene != NetworkManager.SceneManager.DontDestroyOnLoadScene)
                {
                    SpawnedObjectsList.Remove(sobj);
                    UnityEngine.Object.Destroy(sobj.gameObject);
                }
            }
        }

        internal void DespawnAndDestroyNetworkObjects()
        {
            var networkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>();

            for (int i = 0; i < networkObjects.Length; i++)
            {
                if (networkObjects[i].NetworkManager == NetworkManager)
                {
                    if (NetworkManager.PrefabHandler.ContainsHandler(networkObjects[i]))
                    {
                        OnDespawnObject(networkObjects[i], false);
                        // Leave destruction up to the handler
                        NetworkManager.PrefabHandler.HandleNetworkPrefabDestroy(networkObjects[i]);
                    }
                    else if (networkObjects[i].IsSpawned)
                    {
                        // If it is an in-scene placed NetworkObject then just despawn
                        // and let it be destroyed when the scene is unloaded. Otherwise, despawn and destroy it.
                        var shouldDestroy = !(networkObjects[i].IsSceneObject != null && networkObjects[i].IsSceneObject.Value);

                        OnDespawnObject(networkObjects[i], shouldDestroy);
                    }
                    else if (networkObjects[i].IsSceneObject != null && !networkObjects[i].IsSceneObject.Value)
                    {
                        UnityEngine.Object.Destroy(networkObjects[i].gameObject);
                    }
                }
            }
        }

        internal void DestroySceneObjects()
        {
            var networkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>();

            for (int i = 0; i < networkObjects.Length; i++)
            {
                if (networkObjects[i].NetworkManager == NetworkManager)
                {
                    if (networkObjects[i].IsSceneObject == null || networkObjects[i].IsSceneObject.Value == true)
                    {
                        if (NetworkManager.PrefabHandler.ContainsHandler(networkObjects[i]))
                        {
                            NetworkManager.PrefabHandler.HandleNetworkPrefabDestroy(networkObjects[i]);
                            if (SpawnedObjects.ContainsKey(networkObjects[i].NetworkObjectId))
                            {
                                OnDespawnObject(networkObjects[i], false);
                            }
                        }
                        else
                        {
                            UnityEngine.Object.Destroy(networkObjects[i].gameObject);
                        }
                    }
                }
            }
        }

        internal void ServerSpawnSceneObjectsOnStartSweep()
        {
            var networkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>();
            var networkObjectsToSpawn = new List<NetworkObject>();

            for (int i = 0; i < networkObjects.Length; i++)
            {
                if (networkObjects[i].NetworkManager == NetworkManager)
                {
                    if (networkObjects[i].IsSceneObject == null)
                    {
                        networkObjectsToSpawn.Add(networkObjects[i]);
                    }
                }
            }


            foreach (var networkObject in networkObjectsToSpawn)
            {
                SpawnNetworkObjectLocally(networkObject, GetNetworkObjectId(), true, false, networkObject.OwnerClientId, true);
            }
        }

        internal void OnDespawnObject(NetworkObject networkObject, bool destroyGameObject)
        {
            if (NetworkManager == null)
            {
                return;
            }

            // We have to do this check first as subsequent checks assume we can access NetworkObjectId.
            if (networkObject == null)
            {
                Debug.LogWarning($"Trying to destroy network object but it is null");
                return;
            }

            // Removal of spawned object
            if (!SpawnedObjects.ContainsKey(networkObject.NetworkObjectId))
            {
                Debug.LogWarning($"Trying to destroy object {networkObject.NetworkObjectId} but it doesn't seem to exist anymore!");
                return;
            }

            // If we are shutting down the NetworkManager, then ignore resetting the parent
            if (!NetworkManager.ShutdownInProgress)
            {
                // Move child NetworkObjects to the root when parent NetworkObject is destroyed
                foreach (var spawnedNetObj in SpawnedObjectsList)
                {
                    var (isReparented, latestParent) = spawnedNetObj.GetNetworkParenting();
                    if (isReparented && latestParent == networkObject.NetworkObjectId)
                    {
                        spawnedNetObj.gameObject.transform.parent = null;

                        if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
                        {
                            NetworkLog.LogWarning($"{nameof(NetworkObject)} #{spawnedNetObj.NetworkObjectId} moved to the root because its parent {nameof(NetworkObject)} #{networkObject.NetworkObjectId} is destroyed");
                        }
                    }
                }
            }

            networkObject.InvokeBehaviourNetworkDespawn();

            if (NetworkManager != null && NetworkManager.IsServer)
            {
                if (NetworkManager.NetworkConfig.RecycleNetworkIds)
                {
                    ReleasedNetworkObjectIds.Enqueue(new ReleasedNetworkId()
                    {
                        NetworkId = networkObject.NetworkObjectId,
                        ReleaseTime = Time.unscaledTime
                    });
                }

                if (networkObject != null)
                {
                    // As long as we have any remaining clients, then notify of the object being destroy.
                    if (NetworkManager.ConnectedClientsList.Count > 0)
                    {
                        m_TargetClientIds.Clear();

                        // We keep only the client for which the object is visible
                        // as the other clients have them already despawned
                        foreach (var clientId in NetworkManager.ConnectedClientsIds)
                        {
                            if (networkObject.IsNetworkVisibleTo(clientId))
                            {
                                m_TargetClientIds.Add(clientId);
                            }
                        }

                        var message = new DestroyObjectMessage
                        {
                            NetworkObjectId = networkObject.NetworkObjectId
                        };
                        var size = NetworkManager.SendMessage(ref message, NetworkDelivery.ReliableSequenced, m_TargetClientIds);
                        foreach (var targetClientId in m_TargetClientIds)
                        {
                            NetworkManager.NetworkMetrics.TrackObjectDestroySent(targetClientId, networkObject, size);
                        }
                    }
                }
            }

            networkObject.IsSpawned = false;

            if (SpawnedObjects.Remove(networkObject.NetworkObjectId))
            {
                SpawnedObjectsList.Remove(networkObject);
            }

            var gobj = networkObject.gameObject;
            if (destroyGameObject && gobj != null)
            {
                if (NetworkManager.PrefabHandler.ContainsHandler(networkObject))
                {
                    NetworkManager.PrefabHandler.HandleNetworkPrefabDestroy(networkObject);
                }
                else
                {
                    UnityEngine.Object.Destroy(gobj);
                }
            }
        }

        /// <summary>
        /// Updates all spawned <see cref="NetworkObject.Observers"/> for the specified client
        /// Note: if the clientId is the server then it is observable to all spawned <see cref="NetworkObject"/>'s
        /// </summary>
        internal void UpdateObservedNetworkObjects(ulong clientId)
        {
            foreach (var sobj in SpawnedObjectsList)
            {
                if (sobj.CheckObjectVisibility == null)
                {
                    if (!sobj.Observers.Contains(clientId))
                    {
                        sobj.Observers.Add(clientId);
                    }
                }
                else
                {
                    if (sobj.CheckObjectVisibility(clientId))
                    {
                        sobj.Observers.Add(clientId);
                    }
                    else if (sobj.Observers.Contains(clientId))
                    {
                        sobj.Observers.Remove(clientId);
                    }
                }
            }
        }
    }
}