using NATUPNPLib;
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading.Tasks;

namespace RBG_Server
{
    /// <summary>
    /// Contains all communication data, from both the client's and server's perspective (should be able to switch between each mode as necessary)
    /// </summary>
    /// 
    public class CommunicationHandler
    {
        UPnPNAT upnpnat = new();
        IStaticPortMapping portMapping;
        

        /// <summary>
        /// Image data is stored in memory in a dictionary collection. Each byte[] represents an image file, compressed according to its file type;
        /// which helps save space in memory. Uses a CachedByteArray; essentially a normal byte array but automatically stored on disk if it is larger
        /// than a set size.
        /// This limit can be changed at any time
        /// </summary>
        public ConcurrentDictionary<string, CachedByteArray> ImageCollection { get; } = new();
        public List<string> ImageList {  get; } = new();
        public string BoardName { get; set; }

        public IPAddress IpAddress { get; set; }
        public short Port { get; set; }

        private TcpClient stateRetriever { get; set; }
        private TcpClient dataRetriever { get; set; }


        public int ColumnCount { get;private set; }
        public int RowCount { get;private set; }
        public int ColumnZoomStart { get;private set; }
        public int RowZoomStart { get;private set; }
        public int ColumnZoomSpan { get;private set; }
        public int RowZoomSpan { get;private set; }
        public int StartingColumn { get;private set; }
        public int StartingRow { get;private set; }

        public void InitialiseServer()
        {
            // Find the server's active (reliable) network adapter, by creating a remote connection and retrieving our IP from it:
            using (Socket s = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp))
            {
                s.Bind(new IPEndPoint(IPAddress.Any, 0));
                s.Connect("microsoft.com", 0);
                // The IP is implicitly the one assigned to the interface the OS would use to connect to the remote address
                IpAddress = (s.LocalEndPoint as IPEndPoint).Address;
            }
            // Create the upnp mapping
            upnpnat.StaticPortMappingCollection.Add(Port, "TCP", Port, IpAddress.ToString(), true, "RBGServer");

            TcpListener listener = new(IPAddress.Any, Port); // Allow local comms

            listener.Start();
            while (true)
            {
                TcpClient client = listener.AcceptTcpClient();
                // Delegate to another thread
                _ = Task.Run(() =>
                {
                    AcceptConnections(client);
                });
            }
            // At this point, the ImageCollection will have already been initialised.
            // The name of the board will also be set to <boardname>{0}.<extension>.
            // Server logic, such as accepting players and maintaining communication goes in here
        }

        private void AcceptConnections(TcpClient client)
        {
            throw new NotImplementedException();
        }

        public void InitialiseClient(TcpClient client)
        {
            // At this point, no details about the game are loaded; we must load them from the server (to which we have already connected [no data should have been sent]).
            NetworkStream stateStream = stateRetriever.GetStream();
            Task stateLoader = new Task(async () =>
            {
                // Get game board details
                byte[] buffer = new byte[] { 1, 0, 0, 0, 1 }; 
                stateStream.Write(buffer, 0, buffer.Length);
                // Response size
                var stateResponse = await GetResponse(stateStream, 4);
                // Response data
                stateResponse = await GetResponse(stateStream, GetInt32(stateResponse)); // Get the full response data
                // Board state data
                ColumnCount = GetInt32(stateResponse[..4]);
                RowCount = GetInt32(stateResponse[4..8]);
                ColumnZoomStart = GetInt32(stateResponse[8..12]);
                RowZoomStart = GetInt32(stateResponse[12..16]);
                ColumnZoomSpan = GetInt32(stateResponse[16..20]);
                RowZoomSpan = GetInt32(stateResponse[20..24]);
                StartingColumn = GetInt32(stateResponse[24..28]);
                StartingRow = GetInt32(stateResponse[28..32]);
                // Basic board data loaded; fetch players
                buffer = new byte[] { 1, 0, 0, 0, 2};
                stateStream.Write(buffer, 0, buffer.Length);
                stateResponse = await GetResponse(stateStream, 4);
                stateResponse = await GetResponse(stateStream, GetInt32(stateResponse));
                // state response contains a player list
            });
            


            NetworkStream dataStream = dataRetriever.GetStream();
            Task dataLoader = new Task(async () =>
            {
                byte[] buffer = new byte[] { 2, 0, 0, 0, 128, 0 }; // Get image collection names
                dataStream.Write(buffer, 0, buffer.Length);
                var dataResponse = await GetResponse(stateStream, 4);

                dataResponse = await GetResponse(dataStream, GetInt32(dataResponse));
                List<byte> data = new List<byte>();
                for (int i = 0; i < dataResponse.Length; i++)
                {
                    if (dataResponse[i] != 0)
                    {
                        data.Add(dataResponse[i]);
                    }
                    else
                    {
                        ImageList.Add(Encoding.UTF8.GetString(data.ToArray()));
                        data.Clear();
                    }
                }

                // Load all low-resolution images
                foreach (string item in ImageList)
                {
                    byte[] strBytes = Encoding.ASCII.GetBytes(item);
                    buffer = new byte[strBytes.Length + 6];
                    byte[] lenBytes = GetBytes(strBytes.Length + 6);
                    lenBytes.CopyTo(buffer, 0);
                    buffer[4] = 129; // Download image
                    buffer[5] = 0; // mip_low
                    strBytes.CopyTo(buffer, 6);
                    dataStream.Write(buffer, 0, buffer.Length);
                    // Read the length, then the data
                    dataResponse = await GetResponse(dataStream);
                    dataResponse = await GetResponse(dataStream, GetInt32(dataResponse));
                    ImageCollection.TryAdd(item + "_mip_low", (CachedByteArray)dataResponse);
                }
                // At this point, the minimal amount of work required by the data thread has been done (load all thumbs)
                // When an asset is needed from here, queue a load
            });

            dataLoader.Start();
            stateLoader.Start();


            byte[] buffer = new byte[] {0,0,0,1,1};
            // Writing to the stream is to be considered near constant-time, but reading is non-constant.
            // This application model must be synchronous, but we execute other commands before expecting our response to have arrived (it can complete at any time in that period)
            stateStream.Write(buffer, 0, buffer.Length);
            buffer[0] = 1;
            buffer[3] = 0;
            dataStream.Write(buffer, 0, buffer.Length);
            // A details request is [<uint32, length>, <byte command>]
            // The response is about the same format:
            var stateResponse = GetResponse(stateStream, 4);
            var dataResponse = GetResponse(dataStream, 4);
            // First, load the board state (low mip-map, row definitions, column definitions, zoom position etc.)
            // Retrieval command for the board
            // Then load the player list, and use the low mip for their sprites
            // Then check each loaded image and load the med, then large, then full sprite
            // Then load the low of each unused image (for quick retrieval)
        }

        /// <summary>
        /// Idea is that each response is prefaced by a 4 byte stream length specifier.
        /// This requires a busy wait to achieve, if not all recieved at once.
        /// We retrieve the 
        /// </summary>
        /// <param name="stream"></param>
        /// <param name="targetLength"></param>
        /// <returns></returns>
        private async Task<byte[]> GetResponse(NetworkStream stream, int targetLength=4)
        {
            if (stream.CanRead)
            {
                byte[] buffer = new byte[targetLength];
                StringBuilder myCompleteMessage = new StringBuilder();
                int numberOfBytesRead = 0;

                // Incoming message may be larger than the buffer size.
                do
                {
                    numberOfBytesRead += await stream.ReadAsync(buffer, numberOfBytesRead, targetLength - numberOfBytesRead);
                }
                while (numberOfBytesRead < targetLength);
                return buffer;
            }
            return Array.Empty<byte>();
        }

        static internal byte[] GetBytes(int i)
        {
            byte[] bytes = BitConverter.GetBytes(i);
            if (BitConverter.IsLittleEndian)
            {
                // We need data in big-endian format; so reverse the array
                Array.Reverse(bytes);
            }
            return bytes;
        }

        static internal int GetInt32(byte[] bytes)
        {
            if (BitConverter.IsLittleEndian)
            {
                // We need data in little-endian format; so reverse the array
                Array.Reverse(bytes);
            }
            return BitConverter.ToInt32(bytes, 0);
        }
    }
}