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

using SBRL.Utilities;
using System.Text;
using System.Runtime.CompilerServices;

namespace PixelServer.Net
{
	/// <summary>
	/// Provides a mechanism to broadcast a program's presence on a multicast address and port.
	/// </summary>
	public class DiscoveryBeacon : IDisposable
	{
		TextWriter logger;
		UdpClient beacon;
		/// <summary>
		/// Whether the beacon is currently active.
		/// If true then the beacon needs disposing of properly by calling the Dispose() method before the program ends.
		/// </summary>
		public bool Active { get; private set; } = true;

		string role = "server";

		/// <summary>
		/// The current IP address of the local machine.
		/// </summary>
		/// <remarks>
		/// Setting this value affects the IP address that is broadcast by the beacon.
		/// </remarks>
		public IPAddress LocalIP { get; set; }
		/// <summary>
		/// The (multicast) IP address that the beacon should broadcast to.
		/// </summary>
		public IPAddress DestinationAddress { get; private set; }
		/// <summary>
		/// The multicast endpoint that the beacon will broadcast to.
		/// This value is dynamically generated from the DestinationAddress and Port properties.
		/// </summary>
		public IPEndPoint MulticastChannel { get; private set; }
		/// <summary>
		/// The port that the beacon should broadcast on.
		/// </summary>
		public int Port { get; set; } = 5050;

		public string Role {
			get{
				return role;
			}
			private set {
				if (value.Contains(" "))
					throw new InvalidDataException($"Error: Invalid role '{value}'.");
				role = value;
			}
		}

		/// <summary>
		/// The frequency at which the beacon should emit broadcasts.
		/// </summary>
		public int EmitFrequency { get; set; } = 2000;

		/// <summary>
		/// Initializes a new instance of the <see cref="PixelServer.Net.DiscoveryBeacon"/> class.
		/// </summary>
		/// <param name="inDestAddress">The destination address to broadcast to.</param>
		/// <param name="inPort">The port to broadcast on.</param>
		/// <param name="inLogger">The place to send log messages to defaults to Console.Out.</param>
		public DiscoveryBeacon(IPAddress inDestAddress, int inPort, TextWriter inLogger)
		{
			logger = inLogger;

			Port = inPort;
			DestinationAddress = inDestAddress;
			MulticastChannel = new IPEndPoint(DestinationAddress, Port);

			LocalIP = findLocalIP();
			logger.WriteLine("Using {0} as the local IP Address.", LocalIP);
		}
		/// <summary>
		/// Initializes a new instance of the <see cref="PixelServer.Net.DiscoveryBeacon"/> class.
		/// </summary>
		/// <param name="inDestAddress">The destination address to broadcast to.</param>
		/// <param name="inPort">The port to broadcast on.</param>
		public DiscoveryBeacon(IPAddress inDestAddress, int inPort) : this(inDestAddress, inPort, Console.Out)
		{
		}
		/// <summary>
		/// Initializes a new instance of the <see cref="PixelServer.Net.DiscoveryBeacon"/> class.
		/// </summary>
		/// <param name="inDestAddress">The destination address to broadcast to.</param>
		public DiscoveryBeacon(IPAddress inDestAddress) : this(inDestAddress, 5050)
		{
		}

		/// <summary>
		/// Start the beacon up and broadcast the program's presence on a regular (See <see cref="EmitFrequency"/> basis.
		/// </summary>
		public async Task Emit()
		{
			connect();

			while(true)
			{
				await emitOnce();
				await Task.Delay(EmitFrequency);
			}
		}

		/// <summary>
		/// Finds the IP of the machine the beacon is running on.
		/// </summary>
		/// <returns>The first IP found that points to this machine.</returns>
		private IPAddress findLocalIP()
		{
			List<IPAddress> localIPS = Utilities.GetLocalIps().ToList();
			return localIPS[0];
		}

		/// <summary>
		/// Connects the underlying UdpClient client.
		/// </summary>
		private void connect()
		{
			beacon = new UdpClient(Port);
			Active = true;
			beacon.JoinMulticastGroup(DestinationAddress);
		}
		
		/// <summary>
		/// Emits a single presence broadcast from the beacon.
		/// </summary>
		private async Task emitOnce()
		{
			await Send($"{Role}@{LocalIP}:{Port}\n");
		}

		/// <summary>
		/// Sends a message from the underlying UdpClient to the attached multicast address.
		/// </summary>
		/// <param name="data">The message to send.</param>
		private async Task Send(string data)
		{
			await Send(MulticastChannel, data);
		}
		/// <summary>
		/// Sends a message to the given endpoint using the underlying UdpClient.
		/// </summary>
		/// <param name="destination">The place to send the message to.</param>
		/// <param name="data">The message payload.</param>
		private async Task Send(IPEndPoint destination, string data)
		{
			logger.WriteLine("Sending '{0}' to {1}.", Utilities.EscapeString(data), destination);
			byte[] payload = Encoding.UTF8.GetBytes(data);
			await Send(destination, payload);
		}
		/// <summary>
		/// Sends a raw byte array message to the given endpoint.
		/// This is the lowest level Send() method before the message is passed to the UcpClient itself.
		/// </summary>
		/// <param name="destination">THe destination endpoint to send the message to.</param>
		/// <param name="payload">The byte array to use as the message body.</param>
		private async Task Send(IPEndPoint destination, byte[] payload)
		{
			if (beacon == null)
				throw new InvalidOperationException("Error: Can't send data until you join a channel.");
			await beacon.SendAsync(payload, payload.Length, MulticastChannel);
		}

		/// <summary>
		/// Releases all resource used by the <see cref="PixelServer.Net.DiscoveryBeacon"/>.
		/// </summary>
		/// <remarks>
		/// Call <see cref="Dispose"/> when you are finished using the <see cref="PixelServer.Net.DiscoveryBeacon"/>. The
		/// <see cref="Dispose"/> method leaves the <see cref="PixelServer.Net.DiscoveryBeacon"/> in an unusable state. After
		/// calling <see cref="Dispose"/>, you must release all references to the
		/// <see cref="PixelServer.Net.DiscoveryBeacon"/> so the garbage collector can reclaim the memory that the
		/// <see cref="PixelServer.Net.DiscoveryBeacon"/> was occupying.</remarks>
		public void Dispose()
		{
			beacon.Close();
		}
	}
}