using System.IO;
using System.Linq;
using System.Text;
using JD.Remoting.Exceptions;

namespace JD.Remoting.Details
{
    /// <summary>
    /// The header data of a packet.
    /// </summary>
    internal class PacketHeader
    {
        private static uint _counter = 1;
        private static readonly byte[] _headerInBytes = Encoding.ASCII.GetBytes(PacketHeaderTag + "\0000");

        public const int HeaderSize = 36;
        public const string PacketHeaderTag = "IFT_TCP_HEAD";

        /// <summary>
        /// Body size of all packets (including the message header).
        /// </summary>
        public uint GlobalBodySize;

        /// <summary>
        /// Body size of the current packet.
        /// </summary>
        public uint BodySize;

        /// <summary>
        /// Index of the packet in the current message packets.
        /// </summary>
        public uint Index;

        /// <summary>
        /// Index of the last packet of the message.
        /// </summary>
        public uint MaxIndex;

        /// <summary>
        /// Global id of the message (all the packets of the same message wear the same id).
        /// </summary>
        public uint MessageId;

        public static uint NextMessageId
        {
            get
            {
                unchecked
                {
                    return _counter++;
                }
            }
        }

        public void Read(Stream stream)
        {
            var reader = new BinaryReader(stream);
            var header = reader.ReadBytes(16);

            if (!header.Take(PacketHeaderTag.Length).SequenceEqual(_headerInBytes.Take(PacketHeaderTag.Length))) // Only the ITFPart
            {
                throw new RemotingInvalidDataException("Message header is invalid or not initialized. ");
            }

            GlobalBodySize = reader.ReadUInt32();
            BodySize = reader.ReadUInt32();
            Index = reader.ReadUInt32();
            MaxIndex = reader.ReadUInt32();
            MessageId = reader.ReadUInt32();

            if (MessageId == 0)
            {
                throw new RemotingInvalidDataException("Message header is invalid or not initialized. ");
            }
        }

        public void Write(Stream stream)
        {
            var writer = new BinaryWriter(stream);
            writer.Write(_headerInBytes);
            writer.Write(GlobalBodySize);
            writer.Write(BodySize);
            writer.Write(Index);
            writer.Write(MaxIndex);
            writer.Write(MessageId);
        }
    }
}