using System;
using System.Collections.Generic;

namespace XWorld.Server.Gateway
{
    // pid -> Session。只在 actor 线程被改，故无锁。
    public sealed class SessionManager
    {
        private readonly Dictionary<int, Session> _byPid = new Dictionary<int, Session>();

        public Session OnConnect(int pid, IClientConnection conn)
        {
            if (_byPid.TryGetValue(pid, out var s))
            {
                s.Connection = conn;   // 重连：重绑新连接，保留 RoomId
                s.Connected = true;
                return s;
            }
            s = new Session { PlayerId = pid, Connection = conn, Connected = true };
            _byPid[pid] = s;
            return s;
        }

        public void OnDisconnect(int pid, IClientConnection conn, long currentTick)
        {
            // 仅当断的是"当前连接"才标离线，避免旧连接的迟到断线清掉已重连的新连接
            if (_byPid.TryGetValue(pid, out var s) && ReferenceEquals(s.Connection, conn))
            {
                s.Connected = false;
                s.DisconnectedAtTick = currentTick;
            }
        }

        public IClientConnection GetConnection(int pid)
            => _byPid.TryGetValue(pid, out var s) && s.Connected ? s.Connection : null;

        public bool IsConnected(int pid) => _byPid.TryGetValue(pid, out var s) && s.Connected;

        public Session Get(int pid) => _byPid.TryGetValue(pid, out var s) ? s : null;

        /// <summary>移除断线且"严格越过"重连窗口的会话（currentTick - DisconnectedAtTick &gt; windowTicks）。返回被移除的会话；无则空数组。</summary>
        public IReadOnlyList<Session> SweepExpired(long currentTick, long windowTicks)
        {
            List<Session> removed = null;
            foreach (var kv in _byPid)
            {
                var s = kv.Value;
                if (!s.Connected && currentTick - s.DisconnectedAtTick > windowTicks)
                    (removed ??= new List<Session>()).Add(s);
            }
            if (removed != null)
                foreach (var s in removed) _byPid.Remove(s.PlayerId);
            return removed ?? (IReadOnlyList<Session>)Array.Empty<Session>();
        }
    }
}