Megacity/Assets/Scripts/Gameplay/Netcode/VerifyPlayerDisconnectedSystem.cs

using Unity.Burst;
using Unity.Entities;
using Unity.NetCode;
using Unity.NetCode.Extensions;
using static Unity.Entities.SystemAPI;

namespace Unity.MegaCity.Gameplay
{
    /// <summary>
    /// Verify if a player has been disconnected from the game.
    /// </summary>
    [BurstCompile]
    [WorldSystemFilter(WorldSystemFilterFlags.ServerSimulation)]
    public partial struct VerifyPlayerDisconnectedSystem : ISystem
    {
        private EntityQuery m_ConnectedPlayers;
        public void OnCreate(ref SystemState state)
        {
            var myEntity = state.EntityManager.CreateEntity();
            state.EntityManager.AddBuffer<PlayerConnectedElement>(myEntity);
            m_ConnectedPlayers = state.GetEntityQuery(ComponentType.ReadOnly<NetworkStreamConnection>());
        }

        public void OnUpdate(ref SystemState state)
        {
            var playersConnected = GetSingletonBuffer<PlayerConnectedElement>();

            for (int i = 0; i < playersConnected.Length; i++)
            {
                var player = playersConnected[i];
                if (!state.EntityManager.Exists(player.Value))
                {
                    var playerId = player.PlayerId.ToString();

                    UnityEngine.Debug.Log($"Attention: Player {player.Name}({playerId}) has been disconnected from the game." +
                                          $"\nConnected Players: {m_ConnectedPlayers.CalculateEntityCount()}");
                    playersConnected.RemoveAt(i);

                    // if there is no player connected, auto shut down.
                    if(m_ConnectedPlayers.CalculateEntityCount() == 0)
                    {
                        int ttlInSeconds = 10;
                        UnityEngine.Debug.Log($"Attention: There is no player connected. The game will be over in {ttlInSeconds}s.");
                        MultiverseSDKWrapper.Instance.ShutdownMultiverseInTTL(ttlInSeconds);
                    }
                }
            }
        }
    }
}