tbf/TBF/Rig/TestMethods/iPerlCommunication/communication/C4/IperlHatProtocol/IperlHatFrameParser.cs

using System;
using System.Collections.Generic;

namespace TBF.Rig.TestMethods.iPerlCommunication.communication.C4.IperlHatProtocol
{
    public sealed class IperlHatFrameParser
    {

        public IperlHatResponse Parse(byte[] data)
        {
            if (data == null)
                throw new ArgumentNullException(nameof(data));

            if (data.Length < 5)
                throw new FormatException("Frame too short.");

            
            
            if (data[0] != TestMethods.iPerlCommunication.communication.C4.IperlHatProtocol.IperlHatProtocolConstants.Start)
            {
                //if version parse version 
                if (data[0] == TestMethods.iPerlCommunication.communication.C4.IperlHatProtocol.IperlHatProtocolConstants.Question)
                {
                    //Define Question answer
                    var prefix = new List<byte>{ TestMethods.iPerlCommunication.communication.C4.IperlHatProtocol.IperlHatProtocolConstants.Question };
                    var end = new List<byte>{ TestMethods.iPerlCommunication.communication.C4.IperlHatProtocol.IperlHatProtocolConstants.End };
                    
                    if (IsPrefixValid(data, prefix, end))
                    {
                        //whole payload may be like "vers: Harry T:B800, V:06.06.01, FW:190215, 7ECE, B1.6.01, HW:4, Serial:0"
                        prefix = new List<byte>{ TestMethods.iPerlCommunication.communication.C4.IperlHatProtocol.IperlHatProtocolConstants.Question };
                        byte[] payloadVersion = ExtractPayloadUsePrefix(data, prefix, end);
                        return new IperlHatResponse(TestMethods.iPerlCommunication.communication.C4.IperlHatProtocol.IperlHatProtocolConstants.Question, payloadVersion.Length > 0 ? TestMethods.iPerlCommunication.communication.C4.IperlHatProtocol.IperlHatProtocolConstants.StatusOk : TestMethods.iPerlCommunication.communication.C4.IperlHatProtocol.IperlHatProtocolConstants.StatusNok, payloadVersion);    
                    }
                }

                throw new FormatException("Invalid START byte.");
            }

            if (data[1] != TestMethods.iPerlCommunication.communication.C4.IperlHatProtocol.IperlHatProtocolConstants.Read)
                throw new FormatException("Frame is no Response.");
            
            byte length = data[2];
            if (length != data.Length)
                throw new FormatException("Length mismatch.");

            byte direction = data[1];
            byte status = data[3];
            
            var prefixCommand = new List<byte>{ TestMethods.iPerlCommunication.communication.C4.IperlHatProtocol.IperlHatProtocolConstants.Start,direction,length,status };
            var endCommand = new List<byte>{ TestMethods.iPerlCommunication.communication.C4.IperlHatProtocol.IperlHatProtocolConstants.End };

            byte[] payload = ExtractPayloadUsePrefix(data,prefixCommand,endCommand);

            return new IperlHatResponse(0x00, status, payload);
        }


        private static byte[] ExtractPayloadUsePrefix(
            byte[] data,
            List<byte> prefix,
            List<byte> end)
        {
            if (!IsPrefixValid(data, prefix, end))
                return Array.Empty<byte>();

            int payloadLength = data.Length - (prefix.Count + end.Count);

            if (payloadLength <= 0)
                return Array.Empty<byte>();

            byte[] payload = new byte[payloadLength];

            Buffer.BlockCopy(
                data,
                prefix.Count,
                payload,
                0,
                payloadLength);

            return payload;
        }

        private static bool IsPrefixValid(
            byte[] data,
            List<byte> prefix,
            List<byte> end)
        {
            if (data == null ||
                prefix == null ||
                end == null ||
                data.Length < prefix.Count + end.Count)
            {
                return false;
            }

            // Check frame prefix.
            byte[] commandPrefix = new byte[prefix.Count];

            Buffer.BlockCopy(
                data,
                0,
                commandPrefix,
                0,
                prefix.Count);

            if (!StartsWithPrefix(prefix, commandPrefix))
                return false;

            // Check frame ending.
            byte[] commandEnd = new byte[end.Count];

            Buffer.BlockCopy(
                data,
                data.Length - end.Count,
                commandEnd,
                0,
                end.Count);

            if (!StartsWithPrefix(end, commandEnd))
                return false;

            return true;
        }
        
        private static bool StartsWithPrefix(List<byte> data, byte[] prefix)
        {
            if (data.Count < prefix.Length)
                return false;

            for (int i = 0; i < prefix.Length; i++)
            {
                if (data[i] != prefix[i])
                    return false;
            }

            return true;
        }
        
        private static byte[] ExtractVersionPayload(byte[] data)
        {
            // payload exists only if frame longer than:
            // START + LEN + CTRL + STATUS + CHK_HI + CHK_LO = 6 bytes
            if (data.Length <= 5)
                return Array.Empty<byte>();

            int payloadLength = data.Length - 4;
            byte[] payload = new byte[payloadLength];
            Buffer.BlockCopy(data, 5, payload, 0, payloadLength);
            return payload;
        }
    }


}