using DotNetty.Buffers;
using DotNetty.Codecs;
using DotNetty.Transport.Channels;
using log4net;
using Service.Car.Common;

namespace Service.Car.Codec;

public class Decoder : ByteToMessageDecoder
{
    private static readonly ILog Log = LogManager.GetLogger(typeof(Decoder));

    private readonly IByteBuffer[] _delimiters = { Unpooled.CopiedBuffer(CarConst.StartChar) };

    protected override void Decode(IChannelHandlerContext context, IByteBuffer buffer, List<object> output)
    {
        IByteBuffer? delimiter = FindDelimiter(buffer);
        if (delimiter != null)
        {
            //分隔符索引
            int delimiterIndex = IndexOf(buffer, delimiter);
            //帧长索引
            int frameLengthIndex = delimiterIndex + delimiter.Capacity;

            if (delimiterIndex > 0)
            {
                buffer.SkipBytes(delimiterIndex);
                return;
            }

            if (buffer.ReadableBytes < frameLengthIndex + 2)
            {
                // 数据不足，等待更多数据
                return;
            }

            // 读取长度字段
            int frameLength = buffer.GetUnsignedShortLE(buffer.ReaderIndex + frameLengthIndex);

            if (buffer.ReadableBytes < frameLength)
            {
                // 数据不足，等待更多数据
                return;
            }

            buffer.Clear();
        }
    }

    private IByteBuffer? FindDelimiter(IByteBuffer buffer)
    {
        foreach (IByteBuffer delimiter in _delimiters)
        {
            int delimiterIndex = IndexOf(buffer, delimiter);
            if (delimiterIndex >= 0)
            {
                return delimiter;
            }
        }

        return null;
    }

    private static int IndexOf(IByteBuffer haystack, IByteBuffer needle)
    {
        for (int i = haystack.ReaderIndex; i < haystack.WriterIndex; i++)
        {
            int num = i;
            int j;
            for (j = 0; j < needle.Capacity && haystack.GetByte(num) == needle.GetByte(j); j++)
            {
                num++;
                if (num == haystack.WriterIndex && j != needle.Capacity - 1)
                {
                    return -1;
                }
            }

            if (j == needle.Capacity)
            {
                return i - haystack.ReaderIndex;
            }
        }

        return -1;
    }
}