using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;

namespace SocketSniffConsole {
    public enum IPFlags {
        Reserved = 0x80,
        DoNotFragment = 0x40,
        MoreFragments = 0x20
    }

    public enum PacketProtocol {
        Tcp = 6,
        Udp = 57
    }

    public class IPPacket {
        public int Version { get; set; }
        public int HeaderLength { get; set; }
        public int TypeOfService { get; set; }
        public int TotalLength { get; set; }
        public int Identification { get; set; }
        public IPFlags Flags { get; set; }
        public int FragmentOffset { get; set; }
        public int TimeToLive { get; set; }
        public PacketProtocol Protocol { get; set; }
        public int Checksum { get; set; }
        public IPAddress Source { get; set; }
        public IPAddress Destination { get; set; }
        public byte[] Options { get; set; }
        public byte[] Payload { get; set; }

        public IPPacket() {
        }

        public static IPPacket Parse(byte[] raw) {
            IPPacket packet;

            packet = new IPPacket();
            packet.Version = (raw[0] & 0xF0) >> 4;
            packet.HeaderLength = (raw[0] & 0x0F);
            packet.TypeOfService = raw[1];
            packet.TotalLength = (int)IPAddress.NetworkToHostOrder(BitConverter.ToInt16(raw, 2)); // LOL
            packet.Identification = (int)IPAddress.NetworkToHostOrder(BitConverter.ToInt16(raw, 4));
            packet.Flags = (IPFlags)(raw[6] & 0x70);
            packet.FragmentOffset = (BitConverter.ToInt32(raw, 6) & 0x1FFF);
            packet.TimeToLive = raw[8];
            packet.Protocol = (PacketProtocol)raw[9];
            packet.Checksum = (int)IPAddress.NetworkToHostOrder(BitConverter.ToInt16(raw, 10));
            packet.Source = new IPAddress(new byte[] { raw[12], raw[13], raw[14], raw[15] });
            packet.Destination = new IPAddress(new byte[] { raw[16], raw[17], raw[18], raw[19] });

            int optionsLength = packet.HeaderLength * 5 - 20;
            packet.Options = new byte[optionsLength];
            if (optionsLength > 0)
                Array.Copy(raw, 20, packet.Options, 0,  optionsLength);

            int payloadLength = packet.TotalLength - 20 - optionsLength;
            packet.Payload = new byte[payloadLength];
            Array.Copy(raw, 20 + optionsLength, packet.Payload, 0, payloadLength);
            return packet;
        }
    }
}