using System;
using System.Collections.Generic;
using System.Net;
using System.Net.Sockets;

namespace IgniteEngine.Networking
{
    /// <summary>
    /// Class that listens for incoming network connections using the
    /// TCP socket protocol.
    /// </summary>
    public class NetworkServer : Object
    {
        /// <summary>
        /// The default backlog size, which will be used if none is provided.
        /// </summary>
        public const int BACKLOG_SIZE = 100;

        /// <summary>
        /// A list of the active connections to the <see cref="NetworkServer"/>.
        /// </summary>
        public List<NetworkConnection> Connections { get; }

        /// <summary>
        /// Returns true if this server listens for local (server-to-server) connections.
        /// </summary>
        public bool IsInterService => connectionType != NetworkConnectionType.NCT_CLIENT;

        /// <summary>
        /// The type of connections the server is listening for.
        /// </summary>
        private readonly NetworkConnectionType connectionType;

        /// <summary>
        /// The socket that listens for connections.
        /// </summary>
        private readonly Socket socket;

        /// <summary>
        /// Creates a new instance of the <see cref="NetworkServer"/> class.
        /// </summary>
        public NetworkServer(NetworkConnectionType connectionType)
        {
            Connections = new List<NetworkConnection>();
            socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            this.connectionType = connectionType;
        }

        /// <summary>
        /// Places the server in the listening state.
        /// </summary>
        /// <param name="ipAddress">The IP address to listen for connection on.</param>
        /// <param name="port">The port to listen for connections on.</param>
        /// <param name="backlog">The maximum number of pending connections in the queue.</param>
        public void Listen(string ipAddress, ushort port, int backlog = BACKLOG_SIZE)
        {
            if (!IPAddress.TryParse(ipAddress, out var address))
            {
                Debug.LogAssert($"The IPAddress {ipAddress} is invalid.");
                return;
            }

            socket.Bind(new IPEndPoint(address, port));
            socket.Listen(backlog);
            socket.BeginAccept(AcceptConnection, socket);
        }

        /// <summary>
        /// Accepts a pending connection.
        /// </summary>
        /// <param name="e">The status of the operation.</param>
        private void AcceptConnection(IAsyncResult e)
        {
            if (e.AsyncState == null)
            {
                Debug.LogAssert("NetworkServer::AcceptConnection : AsyncState is null");
                return;
            }

            var serverSocket = (Socket) e.AsyncState;
            var clientSocket = serverSocket.EndAccept(e);

            if (clientSocket != null)
            {
                var connection = new NetworkConnection(this, clientSocket, connectionType);
                if (connection.IsConnected)
                {
                    Connections.Add(connection);
                }
            }

            // Begin accepting connections again.
            serverSocket.BeginAccept(AcceptConnection, serverSocket);
        }

        /// <summary>
        /// Destroys the <see cref="NetworkServer"/> instance.
        /// </summary>
        protected override void Destroy()
        {
            // Close() calls the dispose method for us.
            socket.Close();
        }
    }
}