using Sick.SafetyScanners.DataStructures;
using Sick.SafetyScanners.Helpers;

namespace Sick.SafetyScanners.DataProcessing;

/// <summary>
/// Parser for incoming TCP packets in COLA2 format
/// Thread-safe implementation
/// </summary>
public sealed class ParseTcpPacket
{
    private const int HeaderSize = 18; // COLA2 header size
    
    /// <summary>
    /// Gets the expected packet length from the header
    /// Matches: ParseTCPPacket::getExpectedPacketLength in C++
    /// </summary>
    public uint GetExpectedPacketLength(PacketBuffer buffer)
    {
        var bufferData = buffer.GetBuffer();
        var length = ReadWriteHelper.ReadUint32BigEndian(bufferData.Span, 4);
        return length + 8; // for STX and Length which is not included in length datafield
    }
    
    /// <summary>
    /// Gets the request ID from the packet header
    /// Matches: ParseTCPPacket::getRequestID in C++
    /// </summary>
    public ushort GetRequestId(PacketBuffer buffer)
    {
        var bufferData = buffer.GetBuffer();
        return ReadWriteHelper.ReadUint16BigEndian(bufferData.Span, 14);
    }
    
    /// <summary>
    /// Parses the TCP sequence to extract COLA2 header information
    /// Matches: ParseTCPPacket::parseTCPSequence in C++
    /// </summary>
    public ParseResult ParseTcpSequence(PacketBuffer buffer)
    {
        var bufferData = buffer.GetBuffer();
        var span = bufferData.Span;
        
        // Read header fields
        var stx = ReadWriteHelper.ReadUint32BigEndian(span, 0);
        var length = ReadWriteHelper.ReadUint32BigEndian(span, 4);
        var hubCntr = ReadWriteHelper.ReadUint8BigEndian(span, 8);
        var noc = ReadWriteHelper.ReadUint8BigEndian(span, 9);
        var sessionId = ReadWriteHelper.ReadUint32BigEndian(span, 10);
        var requestId = ReadWriteHelper.ReadUint16BigEndian(span, 14);
        var commandType = ReadWriteHelper.ReadUint8BigEndian(span, 16);
        var commandMode = ReadWriteHelper.ReadUint8BigEndian(span, 17);
        
        // Read data payload (everything after header, starting at offset 20)
        // Matches: ParseTCPPacket::readData in C++ - returns data from offset 20
        ReadOnlyMemory<byte> data = ReadOnlyMemory<byte>.Empty;
        if (bufferData.Length >= 20)
        {
            var dataStart = 20;
            data = bufferData[dataStart..];
        }
        
        return new ParseResult
        {
            Stx = stx,
            Length = length,
            HubCntr = hubCntr,
            NoC = noc,
            SessionId = sessionId,
            RequestId = requestId,
            CommandType = commandType,
            CommandMode = commandMode,
            ErrorCode = null,
            Data = data
        };
    }
    
    /// <summary>
    /// Result of parsing a TCP packet
    /// </summary>
    public sealed class ParseResult
    {
        public uint Stx { get; init; }
        public uint Length { get; init; }
        public byte HubCntr { get; init; }
        public byte NoC { get; init; }
        public uint SessionId { get; init; }
        public ushort RequestId { get; init; }
        public byte CommandType { get; init; }
        public byte CommandMode { get; init; }
        public ushort? ErrorCode { get; init; }
        public ReadOnlyMemory<byte> Data { get; init; }
    }
}