Driftology/Assets/Scripts/FusionLauncher.cs

using Fusion;
using Fusion.Sockets;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.SceneManagement;
using UnityEngine.UI;

public class FusionLauncher : MonoBehaviour, INetworkRunnerCallbacks
{
    [Header("Network Runner")]
    public NetworkRunner runner;

    [Header("Lobby UI")]
    public GameObject lobbyUI;
    public Transform lobbyListContainer;
    public GameObject lobbyButtonPrefab;

    private void Start()
    {
        if (runner == null)
        {
            Debug.LogError("Runner is not assigned in the Inspector!");
            return;
        }

        runner.ProvideInput = true;
        runner.AddCallbacks(this);
    }

    public async void CreateLobby()
    {
        string sessionName = "Lobby_" + Random.Range(1000, 9999);

        var result = await runner.StartGame(new StartGameArgs()
        {
            GameMode = GameMode.Host,
            SessionName = sessionName,
            PlayerCount = 2,
            Scene = SceneRef.FromIndex(SceneManager.GetActiveScene().buildIndex),
            SceneManager = gameObject.AddComponent<NetworkSceneManagerDefault>()
        });

        if (result.Ok)
        {
            Debug.Log($"✔ Created Lobby: {sessionName}");
            lobbyUI.SetActive(false);
        }
        else
        {
            Debug.LogError($"✖ Failed to create lobby: {result.ShutdownReason}");
        }
    }

    public async void JoinLobby(string lobbyName)
    {
        var result = await runner.StartGame(new StartGameArgs()
        {
            GameMode = GameMode.Client,
            SessionName = lobbyName,
            Scene = SceneRef.FromIndex(SceneManager.GetActiveScene().buildIndex),
            SceneManager = gameObject.AddComponent<NetworkSceneManagerDefault>()
        });

        if (result.Ok)
        {
            Debug.Log($"✔ Joined Lobby: {lobbyName}");
            lobbyUI.SetActive(false);
        }
        else
        {
            Debug.LogError($"✖ Failed to join lobby: {result.ShutdownReason}");
        }
    }

    public void RefreshLobbyList()
    {
        runner.JoinSessionLobby(SessionLobby.ClientServer); // This triggers OnSessionListUpdated
    }

    public void OnSessionListUpdated(NetworkRunner runner, List<SessionInfo> sessionList)
    {
        foreach (Transform child in lobbyListContainer)
        {
            Destroy(child.gameObject);
        }

        foreach (var session in sessionList)
        {
            if (session.IsOpen && session.IsVisible && session.PlayerCount < session.MaxPlayers)
            {
                GameObject button = Instantiate(lobbyButtonPrefab, lobbyListContainer);
                button.GetComponentInChildren<Text>().text = session.Name;
                button.GetComponent<Button>().onClick.AddListener(() => JoinLobby(session.Name));
            }
        }
    }

    #region INetworkRunnerCallbacks (Empty implementations)

    public void OnConnectedToServer(NetworkRunner runner) { }
    public void OnDisconnectedFromServer(NetworkRunner runner, NetDisconnectReason reason) { }
    public void OnConnectRequest(NetworkRunner runner, NetworkRunnerCallbackArgs.ConnectRequest request, byte[] token) { }
    public void OnConnectFailed(NetworkRunner runner, NetAddress remoteAddress, NetConnectFailedReason reason) { }
    public void OnUserSimulationMessage(NetworkRunner runner, SimulationMessagePtr message) { }
    public void OnShutdown(NetworkRunner runner, ShutdownReason shutdownReason) { }
    public void OnPlayerJoined(NetworkRunner runner, PlayerRef player) { }
    public void OnPlayerLeft(NetworkRunner runner, PlayerRef player) { }
    public void OnInput(NetworkRunner runner, NetworkInput input) { }
    public void OnInputMissing(NetworkRunner runner, PlayerRef player, NetworkInput input) { }
    public void OnObjectEnterAOI(NetworkRunner runner, NetworkObject obj, PlayerRef player) { }
    public void OnObjectExitAOI(NetworkRunner runner, NetworkObject obj, PlayerRef player) { }
    public void OnReliableDataReceived(NetworkRunner runner, PlayerRef player, ReliableKey key, System.ArraySegment<byte> data) { }
    public void OnReliableDataProgress(NetworkRunner runner, PlayerRef player, ReliableKey key, float progress) { }
    public void OnSceneLoadDone(NetworkRunner runner) { }
    public void OnSceneLoadStart(NetworkRunner runner) { }
    public void OnHostMigration(NetworkRunner runner, HostMigrationToken hostMigrationToken) { }
    public void OnCustomAuthenticationResponse(NetworkRunner runner, Dictionary<string, object> data) { }

    #endregion
}