using System;
using System.IO.Ports;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace DeviceCommand.Base
{
    public class Serial_Port : ISerialPort
    {
        public string PortName { get; set; } = "COM1";
        public int BaudRate { get; set; } = 9600;
        public int DataBits { get; set; } = 8;
        public StopBits StopBits { get; set; } = StopBits.One;
        public Parity Parity { get; set; } = Parity.None;
        public int ReadTimeout { get; set; } = 3000;
        public int WriteTimeout { get; set; } = 3000;

        private SerialPort _serialPort;
        public bool IsConnected => _serialPort?.IsOpen ?? false;
        protected readonly SemaphoreSlim commLock = new(1, 1);

        public Serial_Port()
        {
            _serialPort = new SerialPort();
        }

        /// <summary>
        /// 通过 <see cref="SerialPortConfig"/> 一次性配置串口通信参数。
        /// </summary>
        public Serial_Port(SerialPortConfig config) : this()
        {
            if (config == null) return;
            ConfigureDevice(config.PortName, config.BaudRate, config.DataBits, config.StopBits, config.Parity, config.ReadTimeout, config.WriteTimeout);
        }

        public void ConfigureDevice(string portName, int baudRate, int dataBits = 8, StopBits stopBits = StopBits.One, Parity parity = Parity.None, int readTimeout = 3000, int writeTimeout = 3000)
        {
            PortName = portName;
            BaudRate = baudRate;
            DataBits = dataBits;
            StopBits = stopBits;
            Parity = parity;
            ReadTimeout = readTimeout;
            WriteTimeout = writeTimeout;
        }

        public virtual async Task<bool> ConnectAsync(CancellationToken ct = default)
        {
            await commLock.WaitAsync(ct);
            try
            {
                if (_serialPort.IsOpen) _serialPort.Close();

                _serialPort.PortName = PortName;
                _serialPort.BaudRate = BaudRate;
                _serialPort.DataBits = DataBits;
                _serialPort.StopBits = StopBits;
                _serialPort.Parity = Parity;
                _serialPort.ReadTimeout = ReadTimeout;
                _serialPort.WriteTimeout = WriteTimeout;

                _serialPort.Open();
                return true;
            }
            finally
            {
                commLock.Release();
            }
        }

        public virtual void Close()
        {
            if (_serialPort.IsOpen) _serialPort.Close();
        }

        // 内部无锁发送方法，供原子组合操作调用
        private async Task LoglessSendAsync(string data, CancellationToken ct)
        {
            if (!_serialPort.IsOpen) throw new InvalidOperationException("串口未打开。");

            byte[] bytes = Encoding.UTF8.GetBytes(data);
            using var cts = CancellationTokenSource.CreateLinkedTokenSource(ct);
            if (WriteTimeout > 0) cts.CancelAfter(WriteTimeout);

            await _serialPort.BaseStream.WriteAsync(bytes, 0, bytes.Length, cts.Token);
        }

        public async Task SendAsync(string data, CancellationToken ct = default)
        {
            await commLock.WaitAsync(ct);
            try
            {
                await LoglessSendAsync(data, ct);
            }
            finally
            {
                commLock.Release();
            }
        }

        // 内部无锁读取方法，利用 BaseStream 挂起线程，高性能不吃 CPU
        private async Task<string> LoglessReadAsync(string delimiter, CancellationToken ct)
        {
            if (!_serialPort.IsOpen) throw new InvalidOperationException("串口未打开。");

            delimiter ??= "\n";
            var sb = new StringBuilder();
            byte[] buffer = new byte[1024];

            using var cts = CancellationTokenSource.CreateLinkedTokenSource(ct);
            if (ReadTimeout > 0) cts.CancelAfter(ReadTimeout);

            while (!cts.Token.IsCancellationRequested)
            {
                // 核心优化：利用流异步挂起，替代原先的 BytesToRead 循环延时
                int bytesRead = await _serialPort.BaseStream.ReadAsync(buffer, 0, buffer.Length, cts.Token);
                if (bytesRead == 0) continue;

                sb.Append(Encoding.UTF8.GetString(buffer, 0, bytesRead));

                int index = sb.ToString().IndexOf(delimiter, StringComparison.Ordinal);
                if (index >= 0)
                {
                    return sb.ToString(0, index).Trim();
                }
            }
            throw new TimeoutException("读取数据超时");
        }

        public async Task<string> ReadAsync(string delimiter = "\n", CancellationToken ct = default)
        {
            await commLock.WaitAsync(ct);
            try
            {
                return await LoglessReadAsync(delimiter, ct);
            }
            finally
            {
                commLock.Release();
            }
        }

        // 核心优化：保证多线程环境下发送和等待回包是一个原子过程
        public async Task<string> WriteReadAsync(string command, string delimiter = "\n", CancellationToken ct = default)
        {
            await commLock.WaitAsync(ct);
            try
            {
                await LoglessSendAsync(command, ct);
                return await LoglessReadAsync(delimiter, ct);
            }
            finally
            {
                commLock.Release();
            }
        }

        public void Dispose()
        {
            _serialPort?.Dispose();
            commLock?.Dispose();
        }
    }
}