using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using Unity.Netcode;
using Unity.Services.Authentication;
using Unity.Services.Core;
using Unity.Services.Multiplayer;
using UnityEngine;

/// <summary>
/// Online hosting/joining over Unity Gaming Services (unified Multiplayer "Sessions" API: Relay + Lobby +
/// anonymous Authentication behind single calls). The Sessions API configures and starts the NGO transport
/// itself, so we do NOT call <see cref="NetworkManager.StartHost"/>/<c>StartClient</c> here -
/// CreateSessionAsync starts the host, JoinSession* starts the client; the usual NetworkManager callbacks
/// then fire exactly as for loopback hosting, so MatchManager, spawning and authority are unaffected.
/// Note the UGS "session" (the public server-list entry) is distinct from the in-game "Lobby" scene.
///
/// Logic layer only, surfaced through the <see cref="Changed"/>/<see cref="SessionsChanged"/> events; the
/// uGUI browser driving it is <see cref="OnlineSessionBrowserUI"/>. Requires the project to be linked to a
/// UGS cloud project (Project Settings > Services) with Relay, Lobby and Authentication (Anonymous)
/// enabled; otherwise sign-in fails with a clear status message.
/// </summary>
[RequireComponent(typeof(NetworkManager))]
[DisallowMultipleComponent]
public class OnlineSessionManager : MonoBehaviour
{
    [Tooltip("Maximum players per hosted session (host included).")]
    public int maxPlayers = 8;

    [Tooltip("Give up on a hosting/joining/sign-in attempt that hangs longer than this many seconds (0 = wait forever).")]
    public float connectTimeoutSeconds = 25f;

    private NetworkManager _net;
    private ISession _session;                 // active session (host or client); null when not in one
    private List<ISessionInfo> _sessions = new List<ISessionInfo>();
    private string _hostName = "";
    private string _status = "Idle";
    private bool _busy;
    private bool _leaving;                      // suppress the defensive leave while an explicit leave is in flight

    /// <summary>Raised when status, busy state, or the connection state changes, so a bound UI can re-render.
    /// Async continuations resume on the main thread, so handlers run there.</summary>
    public event Action Changed;

    /// <summary>Raised after the browsable session list is replaced (a refresh completed).</summary>
    public event Action SessionsChanged;

    public string Status => _status;
    public bool IsBusy => _busy;
    public bool IsConnected => _net && _net.IsListening;
    public IReadOnlyList<ISessionInfo> Sessions => _sessions;

    private void Awake()
    {
        _net = GetComponent<NetworkManager>();
        _hostName = $"{SystemInfo.deviceName} game";
    }

    private void OnEnable()
    {
        if (!_net) return;
        _net.OnServerStarted += OnNetworkStarted;
        _net.OnClientStarted += OnNetworkStarted;
        _net.OnServerStopped += OnNetworkStopped;
        _net.OnClientStopped += OnNetworkStopped;
    }

    private void OnDisable()
    {
        if (!_net) return;
        _net.OnServerStarted -= OnNetworkStarted;
        _net.OnClientStarted -= OnNetworkStarted;
        _net.OnServerStopped -= OnNetworkStopped;
        _net.OnClientStopped -= OnNetworkStopped;
    }

    private void OnNetworkStarted() => Changed?.Invoke();

    // The match-end / disconnect / Shutdown paths stop the NetworkManager without telling UGS. Leave the
    // session here too so the Relay allocation and the public lobby entry are released.
    private void OnNetworkStopped(bool _)
    {
        var stale = _session;
        _session = null;
        if (stale != null && !_leaving) LeaveSilently(stale);
        Changed?.Invoke();
    }

    private async void LeaveSilently(ISession session)
    {
        try { await session.LeaveAsync(); }
        catch (Exception e) { Debug.LogWarning($"[OnlineSession] leave-on-stop failed: {e.Message}"); }
    }

    // ----- Public API (driven by OnlineSessionBrowserUI) -------------------------------------------------

    public void Host() => HostAsync();
    public void Refresh() => RefreshAsync();
    public void Join(string sessionId) => JoinAsync(sessionId);
    public void Disconnect() => DisconnectAsync();

    // ----- Implementation --------------------------------------------------------------------------------

    private void SetStatus(string status)
    {
        _status = status;
        Changed?.Invoke();
    }

    private void SetBusy(bool busy)
    {
        _busy = busy;
        Changed?.Invoke();
    }

    private async Task EnsureSignedInAsync()
    {
        if (UnityServices.State != ServicesInitializationState.Initialized)
        {
            // Anonymous tokens are cached per machine under company/product, NOT per project path - so
            // junction-mirror clones (shared ProjectSettings) would otherwise resolve to one UGS player id
            // and collide on join (409 LobbyConflict). Namespacing the auth cache by a hash of this install's
            // path gives each clone a stable, distinct identity. Harmless in production - separate machines
            // already have separate caches; this only matters for same-machine clone testing.
            var options = new InitializationOptions();
            options.SetProfile(ProfileForThisInstall());
            await Timed(UnityServices.InitializeAsync(options));
        }
        if (!AuthenticationService.Instance.IsSignedIn)
            await Timed(AuthenticationService.Instance.SignInAnonymouslyAsync());
    }

    // Deterministic, regex-safe (^[a-zA-Z0-9_-]{1,30}$) profile derived from the install path, so the same
    // clone is always the same UGS player across restarts - no random per-launch identity, no orphaned ghost
    // players/lobbies piling up. SHA1 over dataPath -> "mirror_" + 12 hex chars = 19 chars (fits the limit).
    private static string ProfileForThisInstall()
    {
        using (var sha1 = System.Security.Cryptography.SHA1.Create())
        {
            var bytes = sha1.ComputeHash(System.Text.Encoding.UTF8.GetBytes(Application.dataPath));
            var name = new System.Text.StringBuilder("mirror_", 19);
            for (int i = 0; i < 6; i++) name.Append(bytes[i].ToString("x2"));
            return name.ToString();
        }
    }

    // Shared busy/sign-in/error skeleton around one session operation; the body carries the
    // op-specific statuses and state. ownsConnection = the op starts NGO (host/join), so a timeout that
    // left the transport half-up must tear it down.
    private async Task RunSessionOpAsync(string failLabel, bool ownsConnection, Func<Task> body)
    {
        SetBusy(true);
        try
        {
            SetStatus("Signing in…");
            await EnsureSignedInAsync();
            await body();
        }
        catch (TimeoutException)
        {
            // A create/join can bring the shared transport up before it hangs; drop that partial host so we
            // don't leave the user "connected" with no session. Only for host/join - a refresh may legitimately
            // run while already hosting, and must not shut that host down.
            if (ownsConnection && IsConnected) _net.Shutdown();
            SetStatus($"{failLabel} timed out after {connectTimeoutSeconds:0}s");
            Debug.LogWarning($"[OnlineSession] {failLabel} timed out after {connectTimeoutSeconds:0}s");
        }
        catch (Exception e)
        {
            SetStatus($"{failLabel} failed: {e.Message}");
            Debug.LogException(e);
        }
        finally { SetBusy(false); }
    }

    // The UGS session calls take no CancellationToken, so a hung host/join/sign-in would otherwise block
    // forever - _busy never clears and the browser UI locks permanently. WhenAny bounds each call. The
    // abandoned op keeps running (hot task, no cooperative cancel), so disposeLate tears down any session
    // that materializes AFTER we reported the timeout - preventing an orphaned Relay allocation / ghost host.
    private async Task<T> Timed<T>(Task<T> op, Func<T, Task> disposeLate = null)
    {
        if (connectTimeoutSeconds <= 0f) return await op;
        using (var timer = new CancellationTokenSource())
        {
            if (await Task.WhenAny(op, Task.Delay(TimeSpan.FromSeconds(connectTimeoutSeconds), timer.Token)) == op)
            {
                timer.Cancel();
                return await op;
            }
        }
        DiscardLate(op, disposeLate);
        throw new TimeoutException($"timed out after {connectTimeoutSeconds:0}s");
    }

    private async Task Timed(Task op)
    {
        if (connectTimeoutSeconds <= 0f) { await op; return; }
        using (var timer = new CancellationTokenSource())
        {
            if (await Task.WhenAny(op, Task.Delay(TimeSpan.FromSeconds(connectTimeoutSeconds), timer.Token)) == op)
            {
                timer.Cancel();
                await op;
                return;
            }
        }
        Observe(op);
        throw new TimeoutException($"timed out after {connectTimeoutSeconds:0}s");
    }

    private static async void DiscardLate<T>(Task<T> op, Func<T, Task> disposeLate)
    {
        T result;
        try { result = await op; }
        catch { return; }                     // op faulted late: nothing was created
        if (disposeLate == null) return;
        try { await disposeLate(result); }
        catch (Exception e) { Debug.LogWarning($"[OnlineSession] late-timeout cleanup failed: {e.Message}"); }
    }

    // Observe an abandoned task so its result/exception is never left unhandled.
    private static async void Observe(Task op)
    {
        try { await op; } catch { }
    }

    // Late-cleanup for a timed-out create/join that yields a session anyway. We share ONE NetworkManager, so
    // leaving `late` also tears down the live transport - only reclaim the ghost when the user hasn't since
    // established a tracked session (a successful retry sets _session). Runs on the main thread: no race.
    private Task LeaveIfDisplaced(ISession late)
        => (late != null && _session == null) ? late.LeaveAsync() : Task.CompletedTask;

    private async void HostAsync()
    {
        if (_busy || IsConnected) return;
        await RunSessionOpAsync("Host", true, async () =>
        {
            SetStatus("Creating session…");
            var options = new SessionOptions
            {
                Name = string.IsNullOrWhiteSpace(_hostName) ? "Chameleon game" : _hostName.Trim(),
                MaxPlayers = Mathf.Max(2, maxPlayers)
            }.WithRelayNetwork();
            _session = await Timed(MultiplayerService.Instance.CreateSessionAsync(options), LeaveIfDisplaced);
            SetStatus($"Hosting \"{_session.Name}\" (code {_session.Code})");
        });
    }

    private async void RefreshAsync()
    {
        if (_busy) return;
        await RunSessionOpAsync("Refresh", false, async () =>
        {
            SetStatus("Querying sessions…");
            var results = await Timed(MultiplayerService.Instance.QuerySessionsAsync(new QuerySessionsOptions()));
            _sessions = new List<ISessionInfo>(results.Sessions);
            SessionsChanged?.Invoke();
            SetStatus($"{_sessions.Count} session(s) found");
        });
    }

    private async void JoinAsync(string sessionId)
    {
        if (_busy || IsConnected || string.IsNullOrEmpty(sessionId)) return;
        await RunSessionOpAsync("Join", true, async () =>
        {
            SetStatus("Joining session…");
            _session = await Timed(MultiplayerService.Instance.JoinSessionByIdAsync(sessionId), LeaveIfDisplaced);
            SetStatus($"Joined \"{_session.Name}\"");
        });
    }

    private async void DisconnectAsync()
    {
        if (_busy) return;

        // A UGS session leaves cleanly (LeaveAsync also tears down the NGO connection). A plain loopback
        // host/client - if one is ever active without a session - just shuts the transport down.
        if (_session != null)
        {
            SetBusy(true);
            _leaving = true;
            var session = _session;
            _session = null;
            try
            {
                SetStatus("Leaving…");
                await session.LeaveAsync();
                SetStatus("Left session");
            }
            catch (Exception e)
            {
                SetStatus($"Leave failed: {e.Message}");
                Debug.LogException(e);
            }
            finally { _leaving = false; SetBusy(false); }
        }
        else if (IsConnected)
        {
            _net.Shutdown();
            SetStatus("Disconnected");
        }
    }
}