using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace WaterBubbleCheck
{
    public class Crc
    {
            
        /// <summary>
        /// 判断数据中crc是否正确
        /// </summary>
        /// <param name="datas">传入的数据后两位是crc</param>
        /// <returns></returns>
        public static bool IsCrcOK(byte[] datas)
        {
            int length = datas.Length-2;

            byte[] bytes = new byte[length];
            Array.Copy(datas, 0, bytes, 0, length);
            byte[] getCrc = GetModbusCrc16(bytes);

            if(getCrc[0]== datas[length]&&getCrc[1]==datas[length+1])
            {
                return true;
            }
            else
            {
                return false;
            }           
        }
        /// <summary>
        /// 传入数据添加两位crc
        /// </summary>
        /// <param name="datas"></param>
        /// <returns></returns>
        public static byte[] GetCRCDatas(byte[] datas)
        {
            int length = datas.Length;
            byte[] crc16 = GetModbusCrc16(datas);
            byte[] crcDatas = new byte[length + 2];
            Array.Copy(datas, crcDatas, length);
            Array.Copy(crc16, 0, crcDatas, length,2);         
            return crcDatas;
        }
         private static byte[] GetModbusCrc16(byte[] bytes)
        {
            byte crcRegister_H = 0xFF, crcRegister_L = 0xFF;// 预置一个值为 0xFFFF 的 16 位寄存器

            byte polynomialCode_H = 0xA0, polynomialCode_L = 0x01;// 多项式码 0xA001

            for (int i = 0; i < bytes.Length; i++)
            {
                crcRegister_L = (byte)(crcRegister_L ^ bytes[i]);

                for (int j = 0; j < 8; j++)
                {
                    byte tempCRC_H = crcRegister_H;
                    byte tempCRC_L = crcRegister_L;

                    crcRegister_H = (byte)(crcRegister_H >> 1);
                    crcRegister_L = (byte)(crcRegister_L >> 1);
                    // 高位右移前最后 1 位应该是低位右移后的第 1 位：如果高位最后一位为 1 则低位右移后前面补 1
                    if ((tempCRC_H & 0x01) == 0x01)
                    {
                        crcRegister_L = (byte)(crcRegister_L | 0x80);
                    }

                    if ((tempCRC_L & 0x01) == 0x01)
                    {
                        crcRegister_H = (byte)(crcRegister_H ^ polynomialCode_H);
                        crcRegister_L = (byte)(crcRegister_L ^ polynomialCode_L);
                    }
                }
            }

            return new byte[] { crcRegister_L, crcRegister_H };
        }

    }
}