using System;
using System.Collections.Generic;
using System.IO;
using System.Security.Cryptography;
using System.Text;

//*****************************************************************************
// Copyright 2020 Sensus GmbH Ludwigshafen. All rights reserved.
// Author: Venkat, Rajeshwar
//*****************************************************************************

namespace Sensus.iPerl.NfcHandler
{
	public static class Tools
	{
		public static bool ByteArrayCompare(byte[] a1, byte[] a2)
		{
			// thanks to https://stackoverflow.com/questions/43289/comparing-two-byte-arrays-in-net
			if (a1.Length != a2.Length)
				return false;

			for (int i = 0; i < a1.Length; i++)
				if (a1[i] != a2[i])
					return false;

			return true;
		}
		public static string SwapHex(string sHex)
		{
			string sResult = "";
			int iPos = sHex.Length - 2;
			while (iPos >= 0)
			{
				sResult += sHex.Substring(iPos, 2);
				sHex = sHex.Remove(iPos, 2);
				iPos = sHex.Length - 2;
			}
			return sResult;
		}
        public static string DecimalToHexString(string value, int size = 1)
        {
            try
            {
                long Lval = long.Parse(value);
                if (size == 1) return Lval.ToString("X2");
                if (size == 2) return Lval.ToString("X4");
                if (size == 4) return Lval.ToString("X8");
            }
            catch (Exception)
            {
                if (size == 1) return "00";
                if (size == 2) return "0000";
                if (size == 4) return "00000000";
            }
            return "00";
        }
        public static string ByteToHexString(byte data)
        {
            List<byte> val = new List<byte>();
            val.Add(data);
            byte[] arr = val.ToArray();
            return BytesToHex(arr); 
        }
        public static string BytesToHex(byte[] data)
		{
			StringBuilder sb = new StringBuilder();
			foreach (byte b in data)
				sb.Append(b.ToString("X2"));

			return sb.ToString();

		}
		public static byte[] HexStringToByteArray(String hexString)
		{
			int numberChars = hexString.Length;
			byte[] bytes = new byte[numberChars / 2];
			for (int i = 0; i < numberChars; i += 2)
			{
				bytes[i / 2] = Convert.ToByte(hexString.Substring(i, 2), 16);
			}
			return bytes;
		}
        public enum InitialCrcValue
		{
			Zeros,
			NonZero1 = 0xffff,
			NonZero2 = 0x1D0F
		}

        public class Crc16Ccitt
		{
            private const ushort poly = 0x1021;
			ushort[] table = new ushort[256];
			ushort initialValue = 0;

            public ushort ComputeChecksum(byte[] bytes)
            {
                ushort crc = this.initialValue;
                for (int i = 0; i < bytes.Length; ++i)
                {
                    crc = (ushort)((crc << 8) ^ table[((crc >> 8) ^ (0xff & bytes[i]))]);
                }
                return crc;
            }
            public byte[] ComputeChecksumBytes(byte[] bytes)
            {
                ushort crc = ComputeChecksum(bytes);
                return BitConverter.GetBytes(crc);
            }
            public Crc16Ccitt(InitialCrcValue initialValue)
			{
				this.initialValue = (ushort) initialValue;
				ushort temp, a;
				for (int i = 0; i < table.Length; ++i)
				{
					temp = 0;
					a = (ushort) (i << 8);
					for (int j = 0; j < 8; ++j)
					{
						if (((temp ^ a) & 0x8000) != 0)
						{
							temp = (ushort) ((temp << 1) ^ poly);
						}
						else
						{
							temp <<= 1;
						}
						a <<= 1;
					}
					table[i] = temp;
				}
			}
			public byte[] calcCRCfromMessage(byte[] message)
			{
				// CRC calculation goes from MessageID to Password
				// For Read this means MsgID (1) + Offset (2) + PayloadLength (1) + Password (2) = 6
				// for write the length of the payload comes on top.
				// STX(1), length(1), CRC(2) and ETX(1) are excluded, in total 5 bytes.
				//
				// the method works both for sending messages (where the CRC and ETX are not in message)
				// and for receiving messages (where the CRC and ETX are included at the end)
				byte[] crc_msg = new byte[message[1]];  // message length is 2nd byte
				Array.Copy(message, 2, crc_msg, 0, crc_msg.Length);
				return ComputeChecksumBytes(crc_msg);
			}
			public string commentCRC(byte[] crc_meter, byte[] crc_computed)
            {
				bool crc_do_match = Tools.ByteArrayCompare(crc_meter, crc_computed);
				string crcComment = crc_do_match ? "ok." : "CRC DOESN'T MATCH!!";
				return "CRC Meter: " + Tools.BytesToHex(crc_meter) + (crc_do_match ? " == " : " != ")
					+ "CRC Computed: " + Tools.BytesToHex(crc_computed) + ". " + crcComment;
			}
			public bool crc_do_match(byte[] a, byte[] b)
            {
				return ByteArrayCompare(a, b);
			}

		}
	}
}