better-tee/Assets/Packages/Mirror/Runtime/NetworkManager.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using UnityEngine;
using UnityEngine.Rendering;
using UnityEngine.SceneManagement;
using UnityEngine.Serialization;

namespace Mirror
{
    /// <summary>
    /// Enumeration of methods of where to spawn player objects in multiplayer games.
    /// </summary>
    public enum PlayerSpawnMethod
    {
        Random,
        RoundRobin
    }

    [AddComponentMenu("Network/NetworkManager")]
    [HelpURL("https://mirror-networking.com/xmldocs/articles/Components/NetworkManager.html")]
    public class NetworkManager : MonoBehaviour
    {
        [Header("Configuration")]

        /// <summary>
        /// A flag to control whether the NetworkManager object is destroyed when the scene changes.
        /// <para>This should be set if your game has a single NetworkManager that exists for the lifetime of the process. If there is a NetworkManager in each scene, then this should not be set.</para>
        /// </summary>
        [FormerlySerializedAs("m_DontDestroyOnLoad")]
        public bool dontDestroyOnLoad = true;

        /// <summary>
        /// Controls whether the program runs when it is in the background.
        /// <para>This is required when multiple instances of a program using networking are running on the same machine, such as when testing using localhost. But this is not recommended when deploying to mobile platforms.</para>
        /// </summary>
        [FormerlySerializedAs("m_RunInBackground")]
        public bool runInBackground = true;

        /// <summary>
        /// Automatically invoke StartServer()
        /// <para>If the application is a Server Build or run with the -batchMode command line arguement, StartServer is automatically invoked.</para>
        /// </summary>
        public bool startOnHeadless = true;

        /// <summary>
        /// Server Update frequency, per second. Use around 60Hz for fast paced games like Counter-Strike to minimize latency. Use around 30Hz for games like WoW to minimize computations. Use around 1-10Hz for slow paced games like EVE.
        /// </summary>
        [Tooltip("Server Update frequency, per second. Use around 60Hz for fast paced games like Counter-Strike to minimize latency. Use around 30Hz for games like WoW to minimize computations. Use around 1-10Hz for slow paced games like EVE.")]
        public int serverTickRate = 30;

        /// <summary>
        /// Enables verbose debug messages in the console
        /// </summary>
        [FormerlySerializedAs("m_ShowDebugMessages")]
        public bool showDebugMessages;

        /// <summary>
        /// The scene to switch to when offline.
        /// <para>Setting this makes the NetworkManager do scene management. This scene will be switched to when a network session is completed - such as a client disconnect, or a server shutdown.</para>
        /// </summary>
        [Scene]
        [FormerlySerializedAs("m_OfflineScene")]
        public string offlineScene = "";

        /// <summary>
        /// The scene to switch to when online.
        /// <para>Setting this makes the NetworkManager do scene management. This scene will be switched to when a network session is started - such as a client connect, or a server listen.</para>
        /// </summary>
        [Scene]
        [FormerlySerializedAs("m_OnlineScene")]
        public string onlineScene = "";

        [Header("Network Info")]

        // transport layer
        [SerializeField]
        protected Transport transport;

        /// <summary>
        /// The network address currently in use.
        /// <para>For clients, this is the address of the server that is connected to. For servers, this is the local address.</para>
        /// </summary>
        [FormerlySerializedAs("m_NetworkAddress")]
        public string networkAddress = "localhost";

        /// <summary>
        /// The maximum number of concurrent network connections to support.
        /// <para>This effects the memory usage of the network layer.</para>
        /// </summary>
        [FormerlySerializedAs("m_MaxConnections")]
        public int maxConnections = 4;

        [Header("Spawn Info")]

        /// <summary>
        /// The default prefab to be used to create player objects on the server.
        /// <para>Player objects are created in the default handler for AddPlayer() on the server. Implementing OnServerAddPlayer overrides this behaviour.</para>
        /// </summary>
        [FormerlySerializedAs("m_PlayerPrefab")]
        public GameObject playerPrefab;

        /// <summary>
        /// A flag to control whether or not player objects are automatically created on connect, and on scene change.
        /// </summary>
        [FormerlySerializedAs("m_AutoCreatePlayer")]
        public bool autoCreatePlayer = true;

        /// <summary>
        /// The current method of spawning players used by the NetworkManager.
        /// </summary>
        [FormerlySerializedAs("m_PlayerSpawnMethod")]
        public PlayerSpawnMethod playerSpawnMethod;

        /// <summary>
        /// List of prefabs that will be registered with the spawning system.
        /// <para>For each of these prefabs, ClientManager.RegisterPrefab() will be automatically invoke.</para>
        /// </summary>
        [FormerlySerializedAs("m_SpawnPrefabs"), HideInInspector]
        public List<GameObject> spawnPrefabs = new List<GameObject>();

        /// <summary>
        /// List of transforms populted by NetworkStartPosition components found in the scene.
        /// </summary>
        public static List<Transform> startPositions = new List<Transform>();

        /// <summary>
        /// This is true if the client loaded a new scene when connecting to the server.
        /// <para>This is set before OnClientConnect is called, so it can be checked there to perform different logic if a scene load occurred.</para>
        /// </summary>
        [NonSerialized]
        public bool clientLoadedScene;

        /// <summary>
        /// Number of active player objects across all connections on the server.
        /// <para>This is only valid on the host / server.</para>
        /// </summary>
        public int numPlayers => NetworkServer.connections.Count(kv => kv.Value.playerController != null);

        /// <summary>
        /// The name of the current network scene.
        /// </summary>
        /// <remarks>
        /// <para>This is populated if the NetworkManager is doing scene management. This should not be changed directly. Calls to ServerChangeScene() cause this to change. New clients that connect to a server will automatically load this scene.</para>
        /// <para>This is used to make sure that all scene changes are initialized by Mirror.</para>
        /// <para>Loading a scene manually wont set networkSceneName, so Mirror would still load it again on start.</para>
        /// </remarks>
        public static string networkSceneName = "";

        /// <summary>
        /// True if the server or client is started and running
        /// <para>This is set True in StartServer / StartClient, and set False in StopServer / StopClient</para>
        /// </summary>
        [NonSerialized]
        public bool isNetworkActive;

        /// <summary>
        /// Obsolete: Use <see cref="NetworkClient"/> directly
        /// <para>For example, use <c>NetworkClient.Send(message)</c> instead of <c>NetworkManager.client.Send(message)</c></para>
        /// </summary>
        [EditorBrowsable(EditorBrowsableState.Never), Obsolete("Use NetworkClient directly, it will be made static soon. For example, use NetworkClient.Send(message) instead of NetworkManager.client.Send(message)")]
        public NetworkClient client => NetworkClient.singleton;

        static int startPositionIndex;

        /// <summary>
        /// NetworkManager singleton
        /// </summary>
        public static NetworkManager singleton;

        static UnityEngine.AsyncOperation loadingSceneAsync;
        static NetworkConnection clientReadyConnection;

        /// <summary>
        /// virtual so that inheriting classes' Awake() can call base.Awake() too
        /// </summary>
        public virtual void Awake()
        {
            Debug.Log("Thank you for using Mirror! https://mirror-networking.com");

            // Set the networkSceneName to prevent a scene reload
            // if client connection to server fails.
            networkSceneName = offlineScene;

            InitializeSingleton();

            // setup OnSceneLoaded callback
            SceneManager.sceneLoaded += OnSceneLoaded;
        }

        /// <summary>
        /// headless mode detection
        /// </summary>
        public static bool isHeadless => SystemInfo.graphicsDeviceType == GraphicsDeviceType.Null;

        /// <summary>
        /// Obsolete: Use <see cref="isHeadless"/> instead.
        /// <para>This is a static property now. This method will be removed by summer 2019.</para>
        /// </summary>
        /// <returns></returns>
        [EditorBrowsable(EditorBrowsableState.Never), Obsolete("Use isHeadless instead of IsHeadless()")]
        public static bool IsHeadless()
        {
            return isHeadless;
        }

        void InitializeSingleton()
        {
            if (singleton != null && singleton == this)
            {
                return;
            }

            // do this early
            LogFilter.Debug = showDebugMessages;

            if (dontDestroyOnLoad)
            {
                if (singleton != null)
                {
                    Debug.LogWarning("Multiple NetworkManagers detected in the scene. Only one NetworkManager can exist at a time. The duplicate NetworkManager will be destroyed.");
                    Destroy(gameObject);
                    return;
                }
                if (LogFilter.Debug) Debug.Log("NetworkManager created singleton (DontDestroyOnLoad)");
                singleton = this;
                if (Application.isPlaying) DontDestroyOnLoad(gameObject);
            }
            else
            {
                if (LogFilter.Debug) Debug.Log("NetworkManager created singleton (ForScene)");
                singleton = this;
            }

            // set active transport AFTER setting singleton.
            // so only if we didn't destroy ourselves.
            Transport.activeTransport = transport;
        }

        /// <summary>
        /// virtual so that inheriting classes' Start() can call base.Start() too
        /// </summary>
        public virtual void Start()
        {
            // headless mode? then start the server
            // can't do this in Awake because Awake is for initialization.
            // some transports might not be ready until Start.
            //
            // (tick rate is applied in StartServer!)
            if (isHeadless && startOnHeadless)
            {
                StartServer();
            }
        }

        // support additive scene loads:
        //   NetworkScenePostProcess disables all scene objects on load, and
        //   * NetworkServer.SpawnObjects enables them again on the server when
        //     calling OnStartServer
        //   * ClientScene.PrepareToSpawnSceneObjects enables them again on the
        //     client after the server sends ObjectSpawnStartedMessage to client
        //     in SpawnObserversForConnection. this is only called when the
        //     client joins, so we need to rebuild scene objects manually again
        // TODO merge this with FinishLoadScene()?
        void OnSceneLoaded(Scene scene, LoadSceneMode mode)
        {
            if (mode == LoadSceneMode.Additive)
            {
                if (NetworkServer.active)
                {
                    // TODO only respawn the server objects from that scene later!
                    NetworkServer.SpawnObjects();
                    Debug.Log("Respawned Server objects after additive scene load: " + scene.name);
                }
                if (NetworkClient.active)
                {
                    ClientScene.PrepareToSpawnSceneObjects();
                    Debug.Log("Rebuild Client spawnableObjects after additive scene load: " + scene.name);
                }
            }
        }

        // NetworkIdentity.UNetStaticUpdate is called from UnityEngine while LLAPI network is active.
        // If we want TCP then we need to call it manually. Probably best from NetworkManager, although this means that we can't use NetworkServer/NetworkClient without a NetworkManager invoking Update anymore.
        /// <summary>
        /// virtual so that inheriting classes' LateUpdate() can call base.LateUpdate() too
        /// </summary>
        public virtual void LateUpdate()
        {
            // call it while the NetworkManager exists.
            // -> we don't only call while Client/Server.Connected, because then we would stop if disconnected and the
            //    NetworkClient wouldn't receive the last Disconnect event, result in all kinds of issues
            NetworkServer.Update();
            NetworkClient.Update();
            UpdateScene();
        }

        /// <summary>
        /// called when quitting the application by closing the window / pressing stop in the editor
        /// <para>virtual so that inheriting classes' OnApplicationQuit() can call base.OnApplicationQuit() too</para>
        /// </summary>
        public virtual void OnApplicationQuit()
        {
            // stop client first
            // (we want to send the quit packet to the server instead of waiting
            //  for a timeout)
            if (NetworkClient.isConnected)
            {
                StopClient();
                print("OnApplicationQuit: stopped client");
            }

            // stop server after stopping client (for proper host mode stopping)
            if (NetworkServer.active)
            {
                StopServer();
                print("OnApplicationQuit: stopped server");
            }

            // stop transport (e.g. to shut down threads)
            // (when pressing Stop in the Editor, Unity keeps threads alive
            //  until we press Start again. so if Transports use threads, we
            //  really want them to end now and not after next start)
            Transport.activeTransport.Shutdown();
        }

        /// <summary>
        /// virtual so that inheriting classes' OnValidate() can call base.OnValidate() too
        /// </summary>
        public virtual void OnValidate()
        {
            // add transport if there is none yet. makes upgrading easier.
            if (transport == null)
            {
                // was a transport added yet? if not, add one
                transport = GetComponent<Transport>();
                if (transport == null)
                {
                    transport = gameObject.AddComponent<TelepathyTransport>();
                    Debug.Log("NetworkManager: added default Transport because there was none yet.");
                }
#if UNITY_EDITOR
                UnityEditor.EditorUtility.SetDirty(gameObject);
#endif
            }

            maxConnections = Mathf.Max(maxConnections, 0); // always >= 0

            if (playerPrefab != null && playerPrefab.GetComponent<NetworkIdentity>() == null)
            {
                Debug.LogError("NetworkManager - playerPrefab must have a NetworkIdentity.");
                playerPrefab = null;
            }
        }

        void RegisterServerMessages()
        {
            NetworkServer.RegisterHandler<ConnectMessage>(OnServerConnectInternal);
            NetworkServer.RegisterHandler<DisconnectMessage>(OnServerDisconnectInternal);
            NetworkServer.RegisterHandler<ReadyMessage>(OnServerReadyMessageInternal);
            NetworkServer.RegisterHandler<AddPlayerMessage>(OnServerAddPlayerInternal);
            NetworkServer.RegisterHandler<RemovePlayerMessage>(OnServerRemovePlayerMessageInternal);
            NetworkServer.RegisterHandler<ErrorMessage>(OnServerErrorInternal);
        }

        /// <summary>
        /// Set the frame rate for a headless server.
        /// <para>Override if you wish to disable the behavior or set your own tick rate.</para>
        /// </summary>
        public virtual void ConfigureServerFrameRate()
        {
            // set a fixed tick rate instead of updating as often as possible
            // * if not in Editor (it doesn't work in the Editor)
            // * if not in Host mode
#if !UNITY_EDITOR
            if (!NetworkClient.active && isHeadless)
            {
                Application.targetFrameRate = serverTickRate;
                Debug.Log("Server Tick Rate set to: " + Application.targetFrameRate + " Hz.");
            }
#endif
        }

        /// <summary>
        /// This starts a new server.
        /// <para>This uses the networkPort property as the listen port.</para>
        /// </summary>
        /// <returns></returns>
        public bool StartServer()
        {
            InitializeSingleton();

            if (runInBackground)
                Application.runInBackground = true;

            ConfigureServerFrameRate();

            if (!NetworkServer.Listen(maxConnections))
            {
                Debug.LogError("StartServer listen failed.");
                return false;
            }

            // call OnStartServer AFTER Listen, so that NetworkServer.active is
            // true and we can call NetworkServer.Spawn in OnStartServer
            // overrides.
            // (useful for loading & spawning stuff from database etc.)
            //
            // note: there is no risk of someone connecting after Listen() and
            //       before OnStartServer() because this all runs in one thread
            //       and we don't start processing connects until Update.
            OnStartServer();

            // this must be after Listen(), since that registers the default message handlers
            RegisterServerMessages();

            if (LogFilter.Debug) Debug.Log("NetworkManager StartServer");
            isNetworkActive = true;

            // Only change scene if the requested online scene is not blank, and is not already loaded
            string loadedSceneName = SceneManager.GetActiveScene().name;
            if (!string.IsNullOrEmpty(onlineScene) && onlineScene != loadedSceneName && onlineScene != offlineScene)
            {
                ServerChangeScene(onlineScene);
            }
            else
            {
                NetworkServer.SpawnObjects();
            }
            return true;
        }

        void RegisterClientMessages()
        {
            NetworkClient.RegisterHandler<ConnectMessage>(OnClientConnectInternal);
            NetworkClient.RegisterHandler<DisconnectMessage>(OnClientDisconnectInternal);
            NetworkClient.RegisterHandler<NotReadyMessage>(OnClientNotReadyMessageInternal);
            NetworkClient.RegisterHandler<ErrorMessage>(OnClientErrorInternal);
            NetworkClient.RegisterHandler<SceneMessage>(OnClientSceneInternal);

            if (playerPrefab != null)
            {
                ClientScene.RegisterPrefab(playerPrefab);
            }
            for (int i = 0; i < spawnPrefabs.Count; i++)
            {
                GameObject prefab = spawnPrefabs[i];
                if (prefab != null)
                {
                    ClientScene.RegisterPrefab(prefab);
                }
            }
        }

        /// <summary>
        /// This starts a network client. It uses the networkAddress and networkPort properties as the address to connect to.
        /// <para>This makes the newly created client connect to the server immediately.</para>
        /// </summary>
        public void StartClient()
        {
            InitializeSingleton();

            if (runInBackground)
                Application.runInBackground = true;

            isNetworkActive = true;

            RegisterClientMessages();

            if (string.IsNullOrEmpty(networkAddress))
            {
                Debug.LogError("Must set the Network Address field in the manager");
                return;
            }
            if (LogFilter.Debug) Debug.Log("NetworkManager StartClient address:" + networkAddress);

            NetworkClient.Connect(networkAddress);

            OnStartClient();
        }

        /// <summary>
        /// This starts a network "host" - a server and client in the same application.
        /// <para>The client returned from StartHost() is a special "local" client that communicates to the in-process server using a message queue instead of the real network. But in almost all other cases, it can be treated as a normal client.</para>
        /// </summary>
        public virtual void StartHost()
        {
            OnStartHost();
            if (StartServer())
            {
                ConnectLocalClient();
                OnStartClient();
            }
        }

        void ConnectLocalClient()
        {
            if (LogFilter.Debug) Debug.Log("NetworkManager StartHost");
            networkAddress = "localhost";
            NetworkServer.ActivateLocalClientScene();
            NetworkClient.ConnectLocalServer();
            RegisterClientMessages();
        }

        /// <summary>
        /// This stops both the client and the server that the manager is using.
        /// </summary>
        public void StopHost()
        {
            OnStopHost();

            StopServer();
            StopClient();
        }

        /// <summary>
        /// Stops the server that the manager is using.
        /// </summary>
        public void StopServer()
        {
            if (!NetworkServer.active)
                return;

            OnStopServer();

            if (LogFilter.Debug) Debug.Log("NetworkManager StopServer");
            isNetworkActive = false;
            NetworkServer.Shutdown();
            if (!string.IsNullOrEmpty(offlineScene))
            {
                ServerChangeScene(offlineScene);
            }
            CleanupNetworkIdentities();
        }

        /// <summary>
        /// Stops the client that the manager is using.
        /// </summary>
        public void StopClient()
        {
            OnStopClient();

            if (LogFilter.Debug) Debug.Log("NetworkManager StopClient");
            isNetworkActive = false;

            // shutdown client
            NetworkClient.Disconnect();
            NetworkClient.Shutdown();

            if (!string.IsNullOrEmpty(offlineScene))
            {
                ClientChangeScene(offlineScene, LoadSceneMode.Single, LocalPhysicsMode.None);
            }
            CleanupNetworkIdentities();
        }

        /// <summary>
        /// This causes the server to switch scenes and sets the networkSceneName.
        /// <para>Clients that connect to this server will automatically switch to this scene. This is called autmatically if onlineScene or offlineScene are set, but it can be called from user code to switch scenes again while the game is in progress. This automatically sets clients to be not-ready. The clients must call NetworkClient.Ready() again to participate in the new scene.</para>
        /// </summary>
        /// <param name="newSceneName"></param>
        public virtual void ServerChangeScene(string newSceneName)
        {
            ServerChangeScene(newSceneName, LoadSceneMode.Single, LocalPhysicsMode.None);
        }

        /// <summary>
        /// This causes the server to switch scenes and sets the networkSceneName.
        /// <para>Clients that connect to this server will automatically switch to this scene. This is called autmatically if onlineScene or offlineScene are set, but it can be called from user code to switch scenes again while the game is in progress. This automatically sets clients to be not-ready. The clients must call NetworkClient.Ready() again to participate in the new scene.</para>
        /// </summary>
        /// <param name="newSceneName"></param>
        /// <param name="sceneMode"></param>
        /// <param name="physicsMode"></param>
        public virtual void ServerChangeScene(string newSceneName, LoadSceneMode sceneMode, LocalPhysicsMode physicsMode)
        {
            if (string.IsNullOrEmpty(newSceneName))
            {
                Debug.LogError("ServerChangeScene empty scene name");
                return;
            }

            if (LogFilter.Debug) Debug.Log("ServerChangeScene " + newSceneName);
            NetworkServer.SetAllClientsNotReady();
            networkSceneName = newSceneName;

            // Let server prepare for scene change
            OnServerChangeScene(newSceneName);

            LoadSceneParameters loadSceneParameters = new LoadSceneParameters(sceneMode, physicsMode);

            loadingSceneAsync = SceneManager.LoadSceneAsync(newSceneName, loadSceneParameters);

            SceneMessage msg = new SceneMessage()
            {
                sceneName = newSceneName,
                sceneMode = loadSceneParameters.loadSceneMode,
                physicsMode = loadSceneParameters.localPhysicsMode
            };

            NetworkServer.SendToAll(msg);

            startPositionIndex = 0;
            startPositions.Clear();
        }

        void CleanupNetworkIdentities()
        {
            foreach (NetworkIdentity identity in Resources.FindObjectsOfTypeAll<NetworkIdentity>())
            {
                identity.MarkForReset();
            }
        }

        internal void ClientChangeScene(string newSceneName, LoadSceneMode sceneMode, LocalPhysicsMode physicsMode)
        {
            if (string.IsNullOrEmpty(newSceneName))
            {
                Debug.LogError("ClientChangeScene empty scene name");
                return;
            }

            if (LogFilter.Debug) Debug.Log("ClientChangeScene newSceneName:" + newSceneName + " networkSceneName:" + networkSceneName);

            // vis2k: pause message handling while loading scene. otherwise we will process messages and then lose all
            // the state as soon as the load is finishing, causing all kinds of bugs because of missing state.
            // (client may be null after StopClient etc.)
            if (LogFilter.Debug) Debug.Log("ClientChangeScene: pausing handlers while scene is loading to avoid data loss after scene was loaded.");
            Transport.activeTransport.enabled = false;

            // Let client prepare for scene change
            OnClientChangeScene(newSceneName);

            loadingSceneAsync = SceneManager.LoadSceneAsync(newSceneName, new LoadSceneParameters()
            {
                loadSceneMode = sceneMode,
                localPhysicsMode = physicsMode,
            });
            networkSceneName = newSceneName; //This should probably not change if additive is used          
        }

        void FinishLoadScene()
        {
            // NOTE: this cannot use NetworkClient.allClients[0] - that client may be for a completely different purpose.

            // process queued messages that we received while loading the scene
            if (LogFilter.Debug) Debug.Log("FinishLoadScene: resuming handlers after scene was loading.");
            Transport.activeTransport.enabled = true;

            if (clientReadyConnection != null)
            {
                clientLoadedScene = true;
                OnClientConnect(clientReadyConnection);
                clientReadyConnection = null;
            }

            if (NetworkServer.active)
            {
                NetworkServer.SpawnObjects();
                OnServerSceneChanged(networkSceneName);
            }

            if (NetworkClient.isConnected)
            {
                RegisterClientMessages();
                OnClientSceneChanged(NetworkClient.connection);
            }
        }

        static void UpdateScene()
        {
            if (singleton != null && loadingSceneAsync != null && loadingSceneAsync.isDone)
            {
                if (LogFilter.Debug) Debug.Log("ClientChangeScene done readyCon:" + clientReadyConnection);
                singleton.FinishLoadScene();
                loadingSceneAsync.allowSceneActivation = true;
                loadingSceneAsync = null;
            }
        }

        /// <summary>
        /// virtual so that inheriting classes' OnDestroy() can call base.OnDestroy() too
        /// </summary>
        public virtual void OnDestroy()
        {
            if (LogFilter.Debug) Debug.Log("NetworkManager destroyed");
        }

        /// <summary>
        /// Registers the transform of a game object as a player spawn location.
        /// <para>This is done automatically by NetworkStartPosition components, but can be done manually from user script code.</para>
        /// </summary>
        /// <param name="start">Transform to register.</param>
        public static void RegisterStartPosition(Transform start)
        {
            if (LogFilter.Debug) Debug.Log("RegisterStartPosition: (" + start.gameObject.name + ") " + start.position);
            startPositions.Add(start);

            // reorder the list so that round-robin spawning uses the start positions
            // in hierarchy order.  This assumes all objects with NetworkStartPosition
            // component are siblings, either in the scene root or together as children
            // under a single parent in the scene.
            startPositions = startPositions.OrderBy(transform => transform.GetSiblingIndex()).ToList();
        }

        /// <summary>
        /// Unregisters the transform of a game object as a player spawn location.
        /// <para>This is done automatically by the <see cref="NetworkStartPosition">NetworkStartPosition</see> component, but can be done manually from user code.</para>
        /// </summary>
        /// <param name="start">Transform to unregister.</param>
        public static void UnRegisterStartPosition(Transform start)
        {
            if (LogFilter.Debug) Debug.Log("UnRegisterStartPosition: (" + start.gameObject.name + ") " + start.position);
            startPositions.Remove(start);
        }

        /// <summary>
        /// Obsolete: Use <see cref="NetworkClient.isConnected"/> instead
        /// </summary>
        /// <returns>Returns True if NetworkClient.isConnected</returns>
        [EditorBrowsable(EditorBrowsableState.Never), Obsolete("Use NetworkClient.isConnected instead")]
        public bool IsClientConnected()
        {
            return NetworkClient.isConnected;
        }

        /// <summary>
        /// This is the only way to clear the singleton, so another instance can be created.
        /// </summary>
        public static void Shutdown()
        {
            if (singleton == null)
                return;

            startPositions.Clear();
            startPositionIndex = 0;
            clientReadyConnection = null;

            singleton.StopHost();
            singleton = null;
        }

        #region Server Internal Message Handlers

        void OnServerConnectInternal(NetworkConnection conn, ConnectMessage connectMsg)
        {
            if (LogFilter.Debug) Debug.Log("NetworkManager.OnServerConnectInternal");

            if (networkSceneName != "" && networkSceneName != offlineScene)
            {
                SceneMessage msg = new SceneMessage() { sceneName = networkSceneName };
                conn.Send(msg);
            }

            OnServerConnect(conn);
        }

        void OnServerDisconnectInternal(NetworkConnection conn, DisconnectMessage msg)
        {
            if (LogFilter.Debug) Debug.Log("NetworkManager.OnServerDisconnectInternal");
            OnServerDisconnect(conn);
        }

        void OnServerReadyMessageInternal(NetworkConnection conn, ReadyMessage msg)
        {
            if (LogFilter.Debug) Debug.Log("NetworkManager.OnServerReadyMessageInternal");
            OnServerReady(conn);
        }

        void OnServerAddPlayerInternal(NetworkConnection conn, AddPlayerMessage extraMessage)
        {
            if (LogFilter.Debug) Debug.Log("NetworkManager.OnServerAddPlayer");

            if (autoCreatePlayer && playerPrefab == null)
            {
                Debug.LogError("The PlayerPrefab is empty on the NetworkManager. Please setup a PlayerPrefab object.");
                return;
            }

            if (autoCreatePlayer && playerPrefab.GetComponent<NetworkIdentity>() == null)
            {
                Debug.LogError("The PlayerPrefab does not have a NetworkIdentity. Please add a NetworkIdentity to the player prefab.");
                return;
            }

            if (conn.playerController != null)
            {
                Debug.LogError("There is already a player for this connection.");
                return;
            }

            OnServerAddPlayer(conn, extraMessage);
        }

        void OnServerRemovePlayerMessageInternal(NetworkConnection conn, RemovePlayerMessage msg)
        {
            if (LogFilter.Debug) Debug.Log("NetworkManager.OnServerRemovePlayerMessageInternal");

            if (conn.playerController != null)
            {
                OnServerRemovePlayer(conn, conn.playerController);
                conn.playerController = null;
            }
        }

        void OnServerErrorInternal(NetworkConnection conn, ErrorMessage msg)
        {
            if (LogFilter.Debug) Debug.Log("NetworkManager.OnServerErrorInternal");
            OnServerError(conn, msg.value);
        }

        #endregion

        #region Client Internal Message Handlers

        void OnClientConnectInternal(NetworkConnection conn, ConnectMessage message)
        {
            if (LogFilter.Debug) Debug.Log("NetworkManager.OnClientConnectInternal");

            string loadedSceneName = SceneManager.GetActiveScene().name;
            if (string.IsNullOrEmpty(onlineScene) || onlineScene == offlineScene || loadedSceneName == onlineScene)
            {
                clientLoadedScene = false;
                OnClientConnect(conn);
            }
            else
            {
                // will wait for scene id to come from the server.
                clientReadyConnection = conn;
            }
        }

        void OnClientDisconnectInternal(NetworkConnection conn, DisconnectMessage msg)
        {
            if (LogFilter.Debug) Debug.Log("NetworkManager.OnClientDisconnectInternal");
            OnClientDisconnect(conn);
        }

        void OnClientNotReadyMessageInternal(NetworkConnection conn, NotReadyMessage msg)
        {
            if (LogFilter.Debug) Debug.Log("NetworkManager.OnClientNotReadyMessageInternal");

            ClientScene.ready = false;
            OnClientNotReady(conn);

            // NOTE: clientReadyConnection is not set here! don't want OnClientConnect to be invoked again after scene changes.
        }

        void OnClientErrorInternal(NetworkConnection conn, ErrorMessage msg)
        {
            if (LogFilter.Debug) Debug.Log("NetworkManager:OnClientErrorInternal");
            OnClientError(conn, msg.value);
        }

        void OnClientSceneInternal(NetworkConnection conn, SceneMessage msg)
        {
            if (LogFilter.Debug) Debug.Log("NetworkManager.OnClientSceneInternal");

            if (NetworkClient.isConnected && !NetworkServer.active)
            {
                ClientChangeScene(msg.sceneName, msg.sceneMode, msg.physicsMode);
            }
        }

        #endregion

        #region Server System Callbacks

        /// <summary>
        /// Called on the server when a new client connects.
        /// <para>Unity calls this on the Server when a Client connects to the Server. Use an override to tell the NetworkManager what to do when a client connects to the server.</para>
        /// </summary>
        /// <param name="conn">Connection from client.</param>
        public virtual void OnServerConnect(NetworkConnection conn) { }

        /// <summary>
        /// Called on the server when a client disconnects.
        /// <para>This is called on the Server when a Client disconnects from the Server. Use an override to decide what should happen when a disconnection is detected.</para>
        /// </summary>
        /// <param name="conn">Connection from client.</param>
        public virtual void OnServerDisconnect(NetworkConnection conn)
        {
            NetworkServer.DestroyPlayerForConnection(conn);
            if (LogFilter.Debug) Debug.Log("OnServerDisconnect: Client disconnected.");
        }

        /// <summary>
        /// Called on the server when a client is ready.
        /// <para>The default implementation of this function calls NetworkServer.SetClientReady() to continue the network setup process.</para>
        /// </summary>
        /// <param name="conn">Connection from client.</param>
        public virtual void OnServerReady(NetworkConnection conn)
        {
            if (conn.playerController == null)
            {
                // this is now allowed (was not for a while)
                if (LogFilter.Debug) Debug.Log("Ready with no player object");
            }
            NetworkServer.SetClientReady(conn);
        }

        /// <summary>
        /// Called on the server when a client adds a new player with ClientScene.AddPlayer.
        /// <para>The default implementation for this function creates a new player object from the playerPrefab.</para>
        /// </summary>
        /// <param name="conn">Connection from client.</param>
        /// <param name="extraMessage">An extra message object passed for the new player.</param>
        public virtual void OnServerAddPlayer(NetworkConnection conn, AddPlayerMessage extraMessage)
        {
            Transform startPos = GetStartPosition();
            GameObject player = startPos != null
                ? Instantiate(playerPrefab, startPos.position, startPos.rotation)
                : Instantiate(playerPrefab);

            NetworkServer.AddPlayerForConnection(conn, player);
        }

        /// <summary>
        /// This finds a spawn position based on NetworkStartPosition objects in the scene.
        /// <para>This is used by the default implementation of OnServerAddPlayer.</para>
        /// </summary>
        /// <returns>Returns the transform to spawn a player at, or null.</returns>
        public Transform GetStartPosition()
        {
            // first remove any dead transforms
            startPositions.RemoveAll(t => t == null);

            if (startPositions.Count == 0)
                return null;

            if (playerSpawnMethod == PlayerSpawnMethod.Random)
            {
                return startPositions[UnityEngine.Random.Range(0, startPositions.Count)];
            }
            else
            {
                Transform startPosition = startPositions[startPositionIndex];
                startPositionIndex = (startPositionIndex + 1) % startPositions.Count;
                return startPosition;
            }
        }

        /// <summary>
        /// Called on the server when a client removes a player.
        /// <para>The default implementation of this function destroys the corresponding player object.</para>
        /// </summary>
        /// <param name="conn">The connection to remove the player from.</param>
        /// <param name="player">The player controller to remove.</param>
        public virtual void OnServerRemovePlayer(NetworkConnection conn, NetworkIdentity player)
        {
            if (player.gameObject != null)
            {
                NetworkServer.Destroy(player.gameObject);
            }
        }

        /// <summary>
        /// Called on the server when a network error occurs for a client connection.
        /// </summary>
        /// <param name="conn">Connection from client.</param>
        /// <param name="errorCode">Error code.</param>
        public virtual void OnServerError(NetworkConnection conn, int errorCode) { }

        /// <summary>
        /// Called from ServerChangeScene immediately before SceneManager.LoadSceneAsync is executed
        /// <para>This allows server to do work / cleanup / prep before the scene changes.</para>
        /// </summary>
        /// <param name="newSceneName">Name of the scene that's about to be loaded</param>
        public virtual void OnServerChangeScene(string newSceneName) { }

        /// <summary>
        /// Called on the server when a scene is completed loaded, when the scene load was initiated by the server with ServerChangeScene().
        /// </summary>
        /// <param name="sceneName">The name of the new scene.</param>
        public virtual void OnServerSceneChanged(string sceneName) { }

        #endregion

        #region Client System Callbacks

        /// <summary>
        /// Called on the client when connected to a server.
        /// <para>The default implementation of this function sets the client as ready and adds a player. Override the function to dictate what happens when the client connects.</para>
        /// </summary>
        /// <param name="conn"></param>
        public virtual void OnClientConnect(NetworkConnection conn)
        {
            if (!clientLoadedScene)
            {
                // Ready/AddPlayer is usually triggered by a scene load completing. if no scene was loaded, then Ready/AddPlayer it here instead.
                if (!ClientScene.ready) ClientScene.Ready(conn);
                if (autoCreatePlayer)
                {
                    ClientScene.AddPlayer();
                }
            }
        }

        /// <summary>
        /// Called on clients when disconnected from a server.
        /// <para>This is called on the client when it disconnects from the server. Override this function to decide what happens when the client disconnects.</para>
        /// </summary>
        /// <param name="conn">Connection to the server.</param>
        public virtual void OnClientDisconnect(NetworkConnection conn)
        {
            StopClient();
        }

        /// <summary>
        /// Called on clients when a network error occurs.
        /// </summary>
        /// <param name="conn">Connection to a server.</param>
        /// <param name="errorCode">Error code.</param>
        public virtual void OnClientError(NetworkConnection conn, int errorCode) { }

        /// <summary>
        /// Called on clients when a servers tells the client it is no longer ready.
        /// <para>This is commonly used when switching scenes.</para>
        /// </summary>
        /// <param name="conn">Connection to a server.</param>
        public virtual void OnClientNotReady(NetworkConnection conn) { }

        /// <summary>
        /// Called from ClientChangeScene immediately before SceneManager.LoadSceneAsync is executed
        /// <para>This allows client to do work / cleanup / prep before the scene changes.</para>
        /// </summary>
        /// <param name="newSceneName">Name of the scene that's about to be loaded</param>
        public virtual void OnClientChangeScene(string newSceneName) { }

        /// <summary>
        /// Called on clients when a scene has completed loaded, when the scene load was initiated by the server.
        /// <para>Scene changes can cause player objects to be destroyed. The default implementation of OnClientSceneChanged in the NetworkManager is to add a player object for the connection if no player object exists.</para>
        /// </summary>
        /// <param name="conn">The network connection that the scene change message arrived on.</param>
        public virtual void OnClientSceneChanged(NetworkConnection conn)
        {
            // always become ready.
            if (!ClientScene.ready) ClientScene.Ready(conn);

            if (autoCreatePlayer && ClientScene.localPlayer == null)
            {
                // add player if existing one is null
                ClientScene.AddPlayer();
            }
        }

        #endregion

        #region Start & Stop callbacks

        // Since there are multiple versions of StartServer, StartClient and StartHost, to reliably customize
        // their functionality, users would need override all the versions. Instead these callbacks are invoked
        // from all versions, so users only need to implement this one case.

        /// <summary>
        /// This is invoked when a host is started.
        /// <para>StartHost has multiple signatures, but they all cause this hook to be called.</para>
        /// </summary>
        public virtual void OnStartHost() { }

        /// <summary>
        /// This is invoked when a server is started - including when a host is started.
        /// <para>StartServer has multiple signatures, but they all cause this hook to be called.</para>
        /// </summary>
        public virtual void OnStartServer() { }

        /// <summary>
        /// Obsolete: Use <see cref="OnStartClient()"/> instead of OnStartClient(NetworkClient client).
        /// <para>All NetworkClient functions are static now, so you can use NetworkClient.Send(message) instead of client.Send(message) directly now.</para>
        /// </summary>
        /// <param name="client">The NetworkClient object that was started.</param>
        [EditorBrowsable(EditorBrowsableState.Never), Obsolete("Use OnStartClient() instead of OnStartClient(NetworkClient client). All NetworkClient functions are static now, so you can use NetworkClient.Send(message) instead of client.Send(message) directly now.")]
        public virtual void OnStartClient(NetworkClient client) { }

        /// <summary>
        /// This is invoked when the client is started.
        /// </summary>
        public virtual void OnStartClient()
        {
#pragma warning disable CS0618 // Type or member is obsolete
            OnStartClient(NetworkClient.singleton);
#pragma warning restore CS0618 // Type or member is obsolete
        }

        /// <summary>
        /// This is called when a server is stopped - including when a host is stopped.
        /// </summary>
        public virtual void OnStopServer() { }

        /// <summary>
        /// This is called when a client is stopped.
        /// </summary>
        public virtual void OnStopClient() { }

        /// <summary>
        /// This is called when a host is stopped.
        /// </summary>
        public virtual void OnStopHost() { }

        #endregion
    }
}