using System;
using System.Text;
/**
* Created by Tong on 2021/9/22.
* link协议粘包拆包
*/
public class LinkMessageDecoder
{

    //instance
    private static LinkMessageDecoder instance = new LinkMessageDecoder();

    //getInstance
    public static LinkMessageDecoder getInstance()
    {
        return instance;
    }

    /**
     * 接收数据缓冲区
     */
    private byte[] byteBuffer;
    private int position;

    private byte[] head = System.Text.Encoding.UTF8.GetBytes("Topic:");

    public LinkMessageDecoder()
    {
        byteBuffer = new byte[1024 * 20];//100K
    }

    /// <summary>
    /// 获取内容长度
    /// </summary>
    /// <param name="topMsgs"></param>
    /// <returns></returns>
    private int getLenght(string[] topMsgs)
    {
        try
        {
            for (int i = 0; i < topMsgs.Length; i++)
            {
                string topMsg = topMsgs[i].Trim();
                if (topMsg.StartsWith("Length:"))
                {
                    return int.Parse(topMsg.Replace("Length:", "").Trim());
                }
            }
        }
        catch (Exception e)
        {
            //LogUtils.e("异常数据：" + topMsgs[0] + "\r\n" + topMsgs[1]);
            return -1;
        }
        //找不到长度
        return -1;
    }

    /// <summary>
    /// 获取主题
    /// </summary>
    /// <param name="topMsgs"></param>
    /// <returns></returns>
    private string getTopic(string[] topMsgs)
    {
        for (int i = 0; i < topMsgs.Length; i++)
        {
            string topMsg = topMsgs[i].Trim();
            if (topMsg.StartsWith("Topic:"))
            {
                return topMsg.Replace("Topic:", "");
            }
        }
        //找不到主题
        return null;
    }

    /**
     * 获取数据的开始位置
     *
     * @return 数据位的开始索引
     */
    private int getBodyIndex()
    {
        byte r = (byte)'\r';
        byte n = (byte)'\n';
        for (int i = 0; i < position; i++)
        {
            //找出数据内容前面的两个换行
            if (3 <= i && byteBuffer[i - 3] == r && byteBuffer[i - 2] == n && byteBuffer[i - 1] == r && byteBuffer[i] == n)
            {
                //剩余的数据
                return i + 1;
            }
        }
        return -1;
    }

    /**
     * 获取头部数据
     *
     * @return
     */
    private string getHeader()
    {
        int bodyIndex = getBodyIndex();
        if (bodyIndex < 0)
        {
            //没有找到头部数据
            return null;
        }
        else
        {
            return System.Text.Encoding.UTF8.GetString(byteBuffer, 0, bodyIndex);
        }
    }

    /**
     * 获取数据内容
     *
     * @param lenght
     * @return
     */
    private byte[] getBody(int index, int lenght)
    {
        //是否已经获取完整所有的数据
        byte[] bodyBytes = new byte[lenght];
        if (index < 0 || position < index + lenght)
        {
            //当前数据还没有接收完成
            return null;
        }

        for (int i = 0; i < bodyBytes.Length; i++)
        {
            bodyBytes[i] = byteBuffer[index + i];
        }
        return bodyBytes;
    }

    /**
     * 移除可能存在的无效数据
     */
    private void removeInVoidBytes()
    {
        int index = 0;
        bool isMatch = false;
        for (; index < position - head.Length; index++)
        {
            isMatch = true;
            for (int j = 0, k = 0; j < head.Length; j++, k++)
            {
                if (head[j] != byteBuffer[index + k])
                {
                    isMatch = false;
                    break;
                }
            }
            if (isMatch)
            {
                break;
            }
        }

        if (0 < index && isMatch)
        {
            int endIndex = position;
            position = 0;
            //byteBuffer.clear();
            for (int i = index; i < endIndex; i++)
            {
                byteBuffer[position++] = byteBuffer[i];
            }
        }
    }

    /**
     * 移除到指定位置前面的数据
     *
     * @param position 指定位置
     */
    private void remove(int index)
    {
        int endIndex = position;
        position = 0;
        //byteBuffer.clear();
        for (int i = index; i < endIndex; i++)
        {
            byteBuffer[position++] = byteBuffer[i];
        }
    }

    public void Decoder(byte[] bytes, Action<string, byte[]> action)
    {
        lock (instance)
        {
            try
            {
                if (null == bytes)
                {
                    return;
                }

                System.Array.Copy(bytes, 0, byteBuffer, position, bytes.Length);
                position += bytes.Length;

                //如果多条命令打包在一条数据中，都需要处理完
                while (true)
                {
                    removeInVoidBytes();//移除可能存在的无效数据

                    //头部数据
                    string header = getHeader();

                    if (header == null)
                    {
                        break;
                    }
                    string[] topMsgs = header.Split("\r\n");

                    string topic = getTopic(topMsgs);
                    int lenght = getLenght(topMsgs);
                    if (topic == null || lenght <= 0)
                    {
                        //获取不到主题或者头部数据还没有接收完成
                        break;
                    }

                    int bodyIndex = getBodyIndex();
                    //是否已经获取完整所有的数据
                    byte[] body = getBody(bodyIndex, lenght);

                    if (body == null)
                    {
                        //当前数据还没有接收完成
                        break;
                    }

                    remove(bodyIndex + lenght);

                    action?.Invoke(topic, body);

                }
            }
            catch (Exception ee)
            {

            }
        }
    }
}