using System.Net.Sockets;
using System.Text;
using System.Text.Json;
using System.IO;

namespace WIDESEAWCS_Tasks.SocketServer
{
    public partial class TcpSocketServer
    {
        /// <summary>
        /// 处理客户端连接的消息循环
        /// </summary>
        /// <remarks>
        /// 持续接收客户端消息，直到连接断开或取消。
        /// 处理流程：
        /// 1. 接收消息（帧解析）
        /// 2. 更新客户端状态（活跃时间、编码）
        /// 3. 处理设备注册
        /// 4. 触发 MessageReceived 事件
        /// 连接断开时清理资源并触发 RobotReceived 事件。
        /// </remarks>
        /// <param name="client">TCP 客户端连接</param>
        /// <param name="clientId">客户端唯一标识</param>
        /// <param name="cancellationToken">取消令牌</param>
        /// <param name="robotCrane">机器人状态</param>
        public async Task HandleClientAsync(TcpClient client, string clientId, CancellationToken cancellationToken, RobotSocketState robotCrane)
        {
            using (client)
            using (NetworkStream networkStream = client.GetStream())
            using (StreamReader reader = new(networkStream, _textEncoding, false, 1024, true))
            using (StreamWriter writer = new(networkStream, _textEncoding, 1024, true) { AutoFlush = true })
            {
                CancellationTokenSource? localCts = null;
                if (_options.EnableHeartbeat || _options.IdleTimeoutSeconds > 0)
                {
                    // 创建链接的取消令牌源
                    localCts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
                }

                try
                {
                    // 消息接收循环
                    while (!cancellationToken.IsCancellationRequested && client.Connected)
                    {
                        string? message;
                        try
                        {
                            var ct = localCts?.Token ?? cancellationToken;
                            // 接收完整消息（帧解析）
                            message = await ReceiveFullMessageAsync(networkStream, _textEncoding, ct);
                        }
                        catch (OperationCanceledException)
                        {
                            break;
                        }

                        if (message == null)
                        {
                            break;
                        }

                        // 更新客户端状态
                        UpdateClientStatus(clientId, message);

                        string messageLower = message.ToLowerInvariant();

                        // 处理注册消息
                        if (TryHandleRegister(messageLower, message, clientId, networkStream, cancellationToken))
                        {
                            continue;
                        }

                        // 触发消息接收事件
                        if (MessageReceived != null)
                        {
                            try
                            {
                                // 判断是否为 JSON 格式
                                bool isJsonFormat = TryParseJsonSilent(message);
                                _ = MessageReceived.Invoke(message, isJsonFormat, client, robotCrane);
                            }
                            catch { }
                        }
                    }
                }
                finally
                {
                    // 清理资源
                    try { localCts?.Cancel(); localCts?.Dispose(); } catch { }
                    RemoveClient(clientId);
                    try { _ = RobotReceived.Invoke(clientId); } catch { }
                }
            }
        }

        /// <summary>
        /// 处理设备注册消息
        /// </summary>
        /// <remarks>
        /// 注册消息格式：register,{deviceId}
        /// 将设备 ID 绑定到当前客户端 ID。
        /// </remarks>
        /// <param name="messageLower">消息小写版本</param>
        /// <param name="message">原始消息</param>
        /// <param name="clientId">客户端 ID</param>
        /// <param name="networkStream">网络流</param>
        /// <param name="cancellationToken">取消令牌</param>
        /// <returns>是否处理了注册消息</returns>
        private bool TryHandleRegister(string messageLower, string message, string clientId, NetworkStream networkStream, CancellationToken cancellationToken)
        {
            if (!messageLower.StartsWith("register,"))
            {
                return false;
            }

            // 提取设备 ID
            string deviceId = message.Substring("register,".Length).Trim();
            if (!string.IsNullOrEmpty(deviceId))
            {
                lock (_syncRoot)
                {
                    // 绑定设备到客户端
                    _deviceBindings[deviceId] = clientId;
                }

                // 回复注册成功
                _ = WriteToClientAsync(clientId, networkStream, $"Registered,{deviceId}", cancellationToken);
            }

            return true;
        }

        /// <summary>
        /// 更新客户端状态
        /// </summary>
        /// <remarks>
        /// 更新最后活跃时间和字符编码。
        /// 如果开启了自动编码检测，根据消息内容判断是 UTF-8 还是 GBK。
        /// </remarks>
        /// <param name="clientId">客户端 ID</param>
        /// <param name="message">最新接收的消息</param>
        private void UpdateClientStatus(string clientId, string message)
        {
            lock (_syncRoot)
            {
                // 更新最后活跃时间
                _clientLastActive[clientId] = DateTime.Now;

                // 如果还没有记录编码
                if (!_clientEncodings.ContainsKey(clientId))
                {
                    if (_options.AutoDetectEncoding && _autoDetectedGb2312 != null)
                    {
                        // 自动检测编码：JSON 或 UTF-8 字节特征则用 UTF-8，否则用 GBK
                        bool isUtf8 = TryParseJsonSilent(message) || IsLikelyUtf8(_textEncoding.GetBytes(message));
                        _clientEncodings[clientId] = isUtf8 ? _textEncoding : _autoDetectedGb2312;
                    }
                    else
                    {
                        _clientEncodings[clientId] = _textEncoding;
                    }
                }
            }
        }

        /// <summary>
        /// 异步发送消息到客户端
        /// </summary>
        /// <remarks>
        /// 内部方法，不使用帧格式，直接发送原始消息。
        /// </remarks>
        private async Task WriteToClientAsync(string clientId, NetworkStream networkStream, string message, CancellationToken cancellationToken)
        {
            SemaphoreSlim? sem = null;
            Encoding? enc = null;
            lock (_syncRoot)
            {
                _clientLocks.TryGetValue(clientId, out sem);
                _clientEncodings.TryGetValue(clientId, out enc);
            }

            enc ??= _textEncoding;

            if (sem != null) await sem.WaitAsync(cancellationToken);
            try
            {
                var framedMessage = BuildFramedMessage(message);
                var data = enc.GetBytes(framedMessage);
                await networkStream.WriteAsync(data, 0, data.Length, cancellationToken);
            }
            finally
            {
                if (sem != null) sem.Release();
            }
        }

        /// <summary>
        /// 构建帧消息
        /// </summary>
        /// <remarks>
        /// 在消息前后添加头尾标识。
        /// </remarks>
        /// <param name="message">原始消息</param>
        /// <returns>带帧标识的消息</returns>
        private string BuildFramedMessage(string message)
        {
            var header = _options.MessageHeader ?? string.Empty;
            var footer = _options.MessageFooter ?? string.Empty;
            return header + (message ?? string.Empty) + footer;
        }

        /// <summary>
        /// 静默尝试解析 JSON
        /// </summary>
        /// <remarks>
        /// 判断消息是否以 { 或 [ 开头，如果是则尝试解析。
        /// 解析失败不抛异常。
        /// </remarks>
        /// <param name="message">消息内容</param>
        /// <returns>是否是有效的 JSON 格式</returns>
        private static bool TryParseJsonSilent(string message)
        {
            if (string.IsNullOrWhiteSpace(message)) return false;
            char c = message.TrimStart()[0];
            if (c != '{' && c != '[') return false;
            try { JsonDocument.Parse(message); return true; } catch { return false; }
        }

        /// <summary>
        /// 判断字节数组是否为 UTF-8 编码
        /// </summary>
        /// <remarks>
        /// 通过检查字节序列是否符合 UTF-8 多字节字符的编码规则。
        /// </remarks>
        /// <param name="data">字节数组</param>
        /// <returns>是否可能是 UTF-8 编码</returns>
        private static bool IsLikelyUtf8(byte[] data)
        {
            int i = 0;
            while (i < data.Length)
            {
                byte b = data[i];
                if (b <= 0x7F) { i++; continue; }  // ASCII 字符

                // 检查多字节字符
                if (b >= 0xC2 && b <= 0xDF)  // 2字节字符
                {
                    if (i + 1 >= data.Length) return false;
                    if ((data[i + 1] & 0xC0) != 0x80) return false;
                    i += 2; continue;
                }
                if (b >= 0xE0 && b <= 0xEF)  // 3字节字符
                {
                    if (i + 2 >= data.Length) return false;
                    if ((data[i + 1] & 0xC0) != 0x80 || (data[i + 2] & 0xC0) != 0x80) return false;
                    i += 3; continue;
                }
                if (b >= 0xF0 && b <= 0xF4)  // 4字节字符
                {
                    if (i + 3 >= data.Length) return false;
                    if ((data[i + 1] & 0xC0) != 0x80 || (data[i + 2] & 0xC0) != 0x80 || (data[i + 3] & 0xC0) != 0x80) return false;
                    i += 4; continue;
                }
                return false;
            }
            return true;
        }

        /// <summary>
        /// 接收完整消息（帧解析）
        /// </summary>
        /// <remarks>
        /// 根据配置的头尾标识解析消息。
        /// 如果未配置头尾，则一直读到数据不可用。
        /// </remarks>
        /// <param name="networkStream">网络流</param>
        /// <param name="encoding">字符编码</param>
        /// <param name="cancellationToken">取消令牌</param>
        /// <returns>接收到的消息</returns>
        private async Task<string?> ReceiveFullMessageAsync(NetworkStream networkStream, Encoding encoding, CancellationToken cancellationToken)
        {
            var header = _options.MessageHeader ?? string.Empty;
            var footer = _options.MessageFooter ?? string.Empty;

            var buffer = new byte[1024];
            var builder = new StringBuilder();

            while (true)
            {
                // 读取数据
                int bytesRead = await networkStream.ReadAsync(buffer.AsMemory(0, buffer.Length), cancellationToken);
                if (bytesRead <= 0)
                {
                    if (builder.Length == 0) return null;
                    // 无头尾配置时，返回已有数据
                    return string.IsNullOrEmpty(header) && string.IsNullOrEmpty(footer) ? builder.ToString() : null;
                }

                builder.Append(encoding.GetString(buffer, 0, bytesRead));

                // 如果没有配置头尾，且数据不可用，返回已有数据
                if (string.IsNullOrEmpty(header) && string.IsNullOrEmpty(footer))
                {
                    if (!networkStream.DataAvailable)
                    {
                        break;
                    }
                    continue;
                }

                // 查找帧头
                var data = builder.ToString();
                var headerIndex = string.IsNullOrEmpty(header) ? 0 : data.IndexOf(header, StringComparison.Ordinal);
                if (headerIndex < 0)
                {
                    continue;
                }

                // 提取帧内容
                var startIndex = headerIndex + header.Length;
                var footerIndex = string.IsNullOrEmpty(footer) ? data.Length : data.IndexOf(footer, startIndex, StringComparison.Ordinal);
                if (footerIndex >= 0)
                {
                    return data.Substring(startIndex, footerIndex - startIndex);
                }
            }

            return builder.ToString();
        }
    }
}