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)
        {
            // payload exists only if frame longer than:
            // START + DIRECTION + LEN + CTRL + END = 5 bytes
            // OR VERSION_START + VERSION = 5 bytes
            if (data.Length <= 5)
                return Array.Empty<byte>();

            //check prefix is equal
            int prefixLength = prefix.Count;
            byte[] commandPrefix = new byte[prefixLength];
            Buffer.BlockCopy(data, 0, commandPrefix, 0, prefixLength);

            if (StartsWithPrefix(end, commandPrefix))
            {
                return Array.Empty<byte>();    
            }
            
            int payloadLength = data.Length - (prefix.Count + end.Count);
            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)
        {
            int prefixLength = prefix.Count;
            // payload exists only if frame longer than:
            // OR VERSION_START + VERSION = 5 bytes - "?VERS" version implemented 
            if (data.Length <= prefixLength) // need be and on END
                return false;

            //check prefix is equal
            byte[] commandPrefix = new byte[prefixLength];
            Buffer.BlockCopy(data, 0, commandPrefix, 0, prefixLength);

            if (StartsWithPrefix(end, commandPrefix))
            {
                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;
        }
    }


}