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

namespace AMWD.Common.Utilities
{
	/// <summary>
	/// Provides some network utils.
	/// </summary>
	public static class NetworkHelper
	{
		/// <summary>
		/// Tries to resolve a <paramref name="hostname"/> to its <see cref="IPAddress"/>es.
		/// </summary>
		/// <param name="hostname">The hostname to resolve.</param>
		/// <param name="addressFamily">An address family to use (available: <see cref="AddressFamily.InterNetwork"/> and <see cref="AddressFamily.InterNetworkV6"/>).</param>
		/// <returns>The resolved <see cref="IPAddress"/>es or an empty list.</returns>
		public static List<IPAddress> ResolveHost(string hostname, AddressFamily addressFamily = default)
		{
			if (string.IsNullOrWhiteSpace(hostname))
				return new();

			if (addressFamily != AddressFamily.InterNetwork && addressFamily != AddressFamily.InterNetworkV6)
				addressFamily = AddressFamily.Unspecified;

			var ipAddress = ResolveIpAddress(hostname, addressFamily);
			// the name was an ip address, should not happen but experience tells other stories
			if (ipAddress != null)
				return new() { ipAddress };

			try
			{
				return Dns.GetHostAddresses(hostname)
					.FilterAddressFamily(addressFamily)
					.ToList();
			}
			catch
			{
				return new();
			}
		}

		/// <summary>
		/// Tries to resolve an interface name to its v4 and v6 <see cref="IPAddress"/>es.
		/// </summary>
		/// <param name="interfaceName">The interface name to resolve.</param>
		/// <param name="addressFamily">An address family to use (available: <see cref="AddressFamily.InterNetwork"/> and <see cref="AddressFamily.InterNetworkV6"/>).</param>
		/// <returns>The resolved <see cref="IPAddress"/>es or an empty list.</returns>
		[System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]   // not possible to define interfaces on unit tests
		public static List<IPAddress> ResolveInterface(string interfaceName, AddressFamily addressFamily = default)
		{
			if (string.IsNullOrWhiteSpace(interfaceName))
				return new();

			if (addressFamily != AddressFamily.InterNetwork && addressFamily != AddressFamily.InterNetworkV6)
				addressFamily = AddressFamily.Unspecified;

			var ipAddress = ResolveIpAddress(interfaceName, addressFamily);
			// the name was an ip address, should not happen but experience tells other stories
			if (ipAddress != null)
				return new() { ipAddress };

			try
			{
				return NetworkInterface.GetAllNetworkInterfaces()
					.Where(nic => nic.Name.Equals(interfaceName, StringComparison.OrdinalIgnoreCase))
					.SelectMany(nic => nic.GetIPProperties().UnicastAddresses.Select(uai => uai.Address))
					.FilterAddressFamily(addressFamily)
					.ToList();
			}
			catch
			{
				return new();
			}
		}

		private static IPAddress ResolveIpAddress(string address, AddressFamily addressFamily)
		{
			if (IPAddress.TryParse(address, out var ipAddress))
			{
				// the address is whether IPv4 nor IPv6
				if (ipAddress.AddressFamily != AddressFamily.InterNetwork && ipAddress.AddressFamily != AddressFamily.InterNetworkV6)
					return null;

				// the address does not match the required address family
				if (addressFamily != AddressFamily.Unspecified && ipAddress.AddressFamily != addressFamily)
					return null;

				return ipAddress;
			}

			return null;
		}

		private static IEnumerable<IPAddress> FilterAddressFamily(this IEnumerable<IPAddress> source, AddressFamily addressFamily)
		{
			return source
				.Where(a => a.AddressFamily == AddressFamily.InterNetwork || a.AddressFamily == AddressFamily.InterNetworkV6)
				.Where(a => addressFamily == AddressFamily.Unspecified || a.AddressFamily == addressFamily)
				.OrderBy(a => a.AddressFamily);
		}
	}
}