using System.Collections.Generic;
using System.IO;
using System.Net;
using System.Text;
using TftpServer.Utils;

namespace TftpServer
{
    public class TftpPacket
    {
        public TftpOpCode OpCode { get; set; }

        public string FileName { get; set; }
        public string Mode { get; set; }

        public short BlockNumber { get; set; }
        public byte[] Data { get; set; }

        public short ErrorNumber { get; set; }
        public string ErrorMessage { get; set; }

        public Dictionary<string, byte> Options { get; set; }

        public TftpPacket(byte[] buffer, int length)
        {
            using var stream = new MemoryStream(buffer);
            using var reader = new BinaryReader(stream);

            OpCode = (TftpOpCode)IPAddress.NetworkToHostOrder(reader.ReadInt16());

            switch (OpCode)
            {
                default: throw new InvalidDataException($"Unknown OpCode: {OpCode} (0x{OpCode:X4})");
                case TftpOpCode.Read:
                    var len = buffer.ScanNullTerminated(stream.Position);
                    FileName = Encoding.ASCII.GetString(buffer, (int)stream.Position, len);
                    stream.Position += len;
                    len = buffer.ScanNullTerminated(stream.Position);
                    Mode = Encoding.ASCII.GetString(buffer, (int)stream.Position, len);
                    stream.Position += len;
                    break;
                case TftpOpCode.Ack:
                    BlockNumber = IPAddress.NetworkToHostOrder(reader.ReadInt16());
                    break;
            }
        }
    }
}