//
// Authors:
//   Ben Motmans <ben.motmans@gmail.com>
//   Lucas Ontivero lucasontivero@gmail.com
//
// Copyright (C) 2007 Ben Motmans
// Copyright (C) 2014 Lucas Ontivero
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
// 
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Sockets;
using System.Threading;
using System.Threading.Tasks;

namespace Open.Nat
{
    internal abstract class Searcher
    {
        private readonly List<NatDevice> _devices = new List<NatDevice>(); 
        protected List<UdpClient> Sockets;
        public EventHandler<DeviceEventArgs> DeviceFound;
        internal DateTime NextSearch = DateTime.UtcNow;

        public async Task<IEnumerable<NatDevice>> Search(CancellationToken cancelationToken)
        {
            await Task.Factory.StartNew(async _ =>
                {
                    NatDiscoverer.TraceSource.LogInfo("Searching for: {0}", GetType().Name);
                    while (!cancelationToken.IsCancellationRequested)
                    {
                        Discover(cancelationToken);
                        Receive(cancelationToken);
                    }
                    CloseSockets();
                }, cancelationToken);
            return _devices;
        }

        private void Discover(CancellationToken cancelationToken)
        {
            if(DateTime.UtcNow < NextSearch) return;

            foreach (var socket in Sockets)
            {
                try
                {
                    Discover(socket, cancelationToken);
                }
                catch (Exception e)
                {
                    NatDiscoverer.TraceSource.LogError("Error searching {0} - Details:", GetType().Name);
                    NatDiscoverer.TraceSource.LogError(e.ToString());
                }
            }
        }

        private void Receive(CancellationToken cancelationToken)
        {
            foreach (var client in Sockets.Where(x=>x.Available>0))
            {
                if(cancelationToken.IsCancellationRequested) return;

                var localHost = ((IPEndPoint)client.Client.LocalEndPoint).Address;
                var receivedFrom = new IPEndPoint(IPAddress.None, 0);
                var buffer = client.Receive(ref receivedFrom);
                var device = AnalyseReceivedResponse(localHost, buffer, receivedFrom);

                if (device != null) RaiseDeviceFound(device);
            }
        }


        protected abstract void Discover(UdpClient client, CancellationToken cancelationToken);

        public abstract NatDevice AnalyseReceivedResponse(IPAddress localAddress, byte[] response, IPEndPoint endpoint);

        public void CloseSockets()
        {
            foreach (var udpClient in Sockets)
            {
                udpClient.Close();
            }
        }

        private void RaiseDeviceFound(NatDevice device)
        {
            _devices.Add(device);
            var handler = DeviceFound;
            if(handler!=null)
                handler(this, new DeviceEventArgs(device));
        }
    }
}