using System;
using LiteNetLib.Utils;

namespace LiteNetLib
{
    internal enum PacketProperty : byte
    {
        Unreliable,
        Channeled,
        Ack,
        Ping,
        Pong,
        ConnectRequest,
        ConnectAccept,
        Disconnect,
        UnconnectedMessage,
        MtuCheck,
        MtuOk,
        Broadcast,
        Merged,
        ShutdownOk,
        PeerNotFound,
        InvalidProtocol,
        NatMessage,
        Empty
    }

    internal sealed class NetPacket
    {
        private static readonly int PropertiesCount = Enum.GetValues(typeof(PacketProperty)).Length;
        private static readonly int[] HeaderSizes;

        static NetPacket()
        {
            HeaderSizes = NetUtils.AllocatePinnedUninitializedArray<int>(PropertiesCount);
            for (int i = 0; i < HeaderSizes.Length; i++)
            {
                switch ((PacketProperty)i)
                {
                    case PacketProperty.Channeled:
                    case PacketProperty.Ack:
                        HeaderSizes[i] = NetConstants.ChanneledHeaderSize;
                        break;
                    case PacketProperty.Ping:
                        HeaderSizes[i] = NetConstants.HeaderSize + 2;
                        break;
                    case PacketProperty.ConnectRequest:
                        HeaderSizes[i] = NetConnectRequestPacket.HeaderSize;
                        break;
                    case PacketProperty.ConnectAccept:
                        HeaderSizes[i] = NetConnectAcceptPacket.Size;
                        break;
                    case PacketProperty.Disconnect:
                        HeaderSizes[i] = NetConstants.HeaderSize + 8;
                        break;
                    case PacketProperty.Pong:
                        HeaderSizes[i] = NetConstants.HeaderSize + 10;
                        break;
                    default:
                        HeaderSizes[i] = NetConstants.HeaderSize;
                        break;
                }
            }
        }

        // Header
        public PacketProperty Property
        {
            get => (PacketProperty)(RawData[0] & 0x1F);
            set => RawData[0] = (byte)((RawData[0] & 0xE0) | (byte)value);
        }
        public byte ConnectionNumber
        {
            get => (byte)((RawData[0] & 0x60) >> 5);
            set => RawData[0] = (byte)((RawData[0] & 0x9F) | (value << 5));
        }
        public ushort Sequence
        {
            get => BitConverter.ToUInt16(RawData, 1);
            set => FastBitConverter.GetBytes(RawData, 1, value);
        }
        public bool IsFragmented => (RawData[0] & 0x80) != 0;

        public void MarkFragmented()
        {
            RawData[0] |= 0x80; // set first bit
        }

        public byte ChannelId
        {
            get => RawData[3];
            set => RawData[3] = value;
        }
        public ushort FragmentId
        {
            get => BitConverter.ToUInt16(RawData, 4);
            set => FastBitConverter.GetBytes(RawData, 4, value);
        }
        public ushort FragmentPart
        {
            get => BitConverter.ToUInt16(RawData, 6);
            set => FastBitConverter.GetBytes(RawData, 6, value);
        }
        public ushort FragmentsTotal
        {
            get => BitConverter.ToUInt16(RawData, 8);
            set => FastBitConverter.GetBytes(RawData, 8, value);
        }

        // Data
        public byte[] RawData;
        public int Size;

        // Delivery
        public object UserData;

        // Pool node
        public NetPacket Next;

        public NetPacket(int size)
        {
            RawData = new byte[size];
            Size = size;
        }

        public NetPacket(PacketProperty property, int size)
        {
            size += GetHeaderSize(property);
            RawData = new byte[size];
            Property = property;
            Size = size;
        }

        public static int GetHeaderSize(PacketProperty property)
        {
            return HeaderSizes[(int)property];
        }

        public int GetHeaderSize()
        {
            return HeaderSizes[RawData[0] & 0x1F];
        }

        public bool Verify()
        {
            byte property = (byte)(RawData[0] & 0x1F);
            if (property >= PropertiesCount)
                return false;
            int headerSize = HeaderSizes[property];
            bool fragmented = (RawData[0] & 0x80) != 0;
            return Size >= headerSize && (!fragmented || Size >= headerSize + NetConstants.FragmentHeaderSize);
        }

#if LITENETLIB_SPANS || NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER || NETCOREAPP2_1 || NETCOREAPP3_1 || NET5_0 || NETSTANDARD2_1
        public static implicit operator Span<byte>(NetPacket p) => new(p.RawData, 0, p.Size);
#endif
    }
}