//using Swan.Net.Dns;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Net.NetworkInformation;
using System.Net.Sockets;
using System.Threading;
using System.Threading.Tasks;

namespace Swan.Net {
  /// <summary>
  /// Provides miscellaneous network utilities such as a Public IP finder,
  /// a DNS client to query DNS records of any kind, and an NTP client.
  /// </summary>
  public static class Network {
    /*/// <summary>
    /// The DNS default port.
    /// </summary>
    public const Int32 DnsDefaultPort = 53;

    /// <summary>
    /// The NTP default port.
    /// </summary>
    public const Int32 NtpDefaultPort = 123;*/

    /// <summary>
    /// Gets the name of the host.
    /// </summary>
    /// <value>
    /// The name of the host.
    /// </value>
    // [Obsolete("NEED", false)]
    public static String HostName => IPGlobalProperties.GetIPGlobalProperties().HostName;

    /*/// <summary>
    /// Gets the name of the network domain.
    /// </summary>
    /// <value>
    /// The name of the network domain.
    /// </value>
    public static String DomainName => IPGlobalProperties.GetIPGlobalProperties().DomainName;

    #region IP Addresses and Adapters Information Methods

    /// <summary>
    /// Gets the active IPv4 interfaces.
    /// Only those interfaces with a valid unicast address and a valid gateway will be returned in the collection.
    /// </summary>
    /// <returns>
    /// A collection of NetworkInterface/IPInterfaceProperties pairs
    /// that represents the active IPv4 interfaces.
    /// </returns>
    public static Dictionary<NetworkInterface, IPInterfaceProperties> GetIPv4Interfaces() {
      // zero conf ip address
      IPAddress zeroConf = new IPAddress(0);

      NetworkInterface[] adapters = NetworkInterface.GetAllNetworkInterfaces().Where(network => network.OperationalStatus == OperationalStatus.Up && network.NetworkInterfaceType != NetworkInterfaceType.Unknown && network.NetworkInterfaceType != NetworkInterfaceType.Loopback).ToArray();

      Dictionary<NetworkInterface, IPInterfaceProperties> result = new Dictionary<NetworkInterface, IPInterfaceProperties>();

      foreach(NetworkInterface adapter in adapters) {
        IPInterfaceProperties properties = adapter.GetIPProperties();
        if(properties == null || properties.GatewayAddresses.Count == 0 || properties.GatewayAddresses.All(gateway => Equals(gateway.Address, zeroConf)) || properties.UnicastAddresses.Count == 0 || properties.GatewayAddresses.All(address => Equals(address.Address, zeroConf)) || properties.UnicastAddresses.Any(a => a.Address.AddressFamily == AddressFamily.InterNetwork) == false) {
          continue;
        }

        result[adapter] = properties;
      }

      return result;
    }

    /// <summary>
    /// Retrieves the local ip addresses.
    /// </summary>
    /// <param name="includeLoopback">if set to <c>true</c> [include loopback].</param>
    /// <returns>An array of local ip addresses.</returns>
    public static IPAddress[] GetIPv4Addresses(Boolean includeLoopback = true) => GetIPv4Addresses(NetworkInterfaceType.Unknown, true, includeLoopback);

    /// <summary>
    /// Retrieves the local ip addresses.
    /// </summary>
    /// <param name="interfaceType">Type of the interface.</param>
    /// <param name="skipTypeFilter">if set to <c>true</c> [skip type filter].</param>
    /// <param name="includeLoopback">if set to <c>true</c> [include loopback].</param>
    /// <returns>An array of local ip addresses.</returns>
    public static IPAddress[] GetIPv4Addresses(NetworkInterfaceType interfaceType, Boolean skipTypeFilter = false, Boolean includeLoopback = false) {
      List<IPAddress> addressList = new List<IPAddress>();
      NetworkInterface[] interfaces = NetworkInterface.GetAllNetworkInterfaces()
          .Where(ni => (skipTypeFilter || ni.NetworkInterfaceType == interfaceType) && ni.OperationalStatus == OperationalStatus.Up).ToArray();

      foreach(NetworkInterface networkInterface in interfaces) {
        IPInterfaceProperties properties = networkInterface.GetIPProperties();

        if(properties.GatewayAddresses.All(g => g.Address.AddressFamily != AddressFamily.InterNetwork)) {
          continue;
        }

        addressList.AddRange(properties.UnicastAddresses.Where(i => i.Address.AddressFamily == AddressFamily.InterNetwork).Select(i => i.Address));
      }

      if(includeLoopback || interfaceType == NetworkInterfaceType.Loopback) {
        addressList.Add(IPAddress.Loopback);
      }

      return addressList.ToArray();
    }

    /// <summary>
    /// Gets the public IP address using ipify.org.
    /// </summary>
    /// <param name="cancellationToken">The cancellation token.</param>
    /// <returns>A public IP address of the result produced by this Task.</returns>
    public static async Task<IPAddress> GetPublicIPAddressAsync(CancellationToken cancellationToken = default) {
      using HttpClient client = new HttpClient();
      HttpResponseMessage response = await client.GetAsync("https://api.ipify.org", cancellationToken).ConfigureAwait(false);
      return IPAddress.Parse(await response.Content.ReadAsStringAsync().ConfigureAwait(false));
    }

    /// <summary>
    /// Gets the configured IPv4 DNS servers for the active network interfaces.
    /// </summary>
    /// <returns>
    /// A collection of NetworkInterface/IPInterfaceProperties pairs
    /// that represents the active IPv4 interfaces.
    /// </returns>
    public static IPAddress[] GetIPv4DnsServers() => GetIPv4Interfaces().Select(a => a.Value.DnsAddresses.Where(d => d.AddressFamily == AddressFamily.InterNetwork)).SelectMany(d => d).ToArray();

    #endregion

    #region DNS and NTP Clients

    /// <summary>
    /// Gets the DNS host entry (a list of IP addresses) for the domain name.
    /// </summary>
    /// <param name="fqdn">The FQDN.</param>
    /// <returns>An array of local ip addresses of the result produced by this task.</returns>
    public static Task<IPAddress[]> GetDnsHostEntryAsync(String fqdn) {
      IPAddress dnsServer = GetIPv4DnsServers().FirstOrDefault() ?? IPAddress.Parse("8.8.8.8");
      return GetDnsHostEntryAsync(fqdn, dnsServer, DnsDefaultPort);
    }

    /// <summary>
    /// Gets the DNS host entry (a list of IP addresses) for the domain name.
    /// </summary>
    /// <param name="fqdn">The FQDN.</param>
    /// <param name="dnsServer">The DNS server.</param>
    /// <param name="port">The port.</param>
    /// <returns>
    /// An array of local ip addresses of the result produced by this task.
    /// </returns>
    /// <exception cref="ArgumentNullException">fqdn.</exception>
    public static async Task<IPAddress[]> GetDnsHostEntryAsync(String fqdn, IPAddress dnsServer, Int32 port) {
      if(fqdn == null) {
        throw new ArgumentNullException(nameof(fqdn));
      }

      if(fqdn.IndexOf(".", StringComparison.Ordinal) == -1) {
        fqdn += "." + IPGlobalProperties.GetIPGlobalProperties().DomainName;
      }

      while(true) {
        if(!fqdn.EndsWith(".", StringComparison.OrdinalIgnoreCase)) {
          break;
        }

        fqdn = fqdn[0..^1];
      }

      DnsClient client = new DnsClient(dnsServer, port);
      IList<IPAddress> result = await client.Lookup(fqdn).ConfigureAwait(false);
      return result.ToArray();
    }

    /// <summary>
    /// Gets the reverse lookup FQDN of the given IP Address.
    /// </summary>
    /// <param name="query">The query.</param>
    /// <param name="dnsServer">The DNS server.</param>
    /// <param name="port">The port.</param>
    /// <returns>A <see cref="System.String" /> that represents the current object.</returns>
    public static Task<String> GetDnsPointerEntryAsync(IPAddress query, IPAddress dnsServer, Int32 port) {
      DnsClient client = new DnsClient(dnsServer, port);
      return client.Reverse(query);
    }

    /// <summary>
    /// Gets the reverse lookup FQDN of the given IP Address.
    /// </summary>
    /// <param name="query">The query.</param>
    /// <returns>A <see cref="System.String" /> that represents the current object.</returns>
    public static Task<String> GetDnsPointerEntryAsync(IPAddress query) {
      DnsClient client = new DnsClient(GetIPv4DnsServers().FirstOrDefault());
      return client.Reverse(query);
    }

    /// <summary>
    /// Queries the DNS server for the specified record type.
    /// </summary>
    /// <param name="query">The query.</param>
    /// <param name="recordType">Type of the record.</param>
    /// <param name="dnsServer">The DNS server.</param>
    /// <param name="port">The port.</param>
    /// <returns>Queries the DNS server for the specified record type of the result produced by this Task.</returns>
    public static async Task<DnsQueryResult> QueryDnsAsync(String query, DnsRecordType recordType, IPAddress dnsServer, Int32 port) {
      if(query == null) {
        throw new ArgumentNullException(nameof(query));
      }

      DnsClient client = new DnsClient(dnsServer, port);
      DnsClient.DnsClientResponse response = await client.Resolve(query, recordType).ConfigureAwait(false);
      return new DnsQueryResult(response);
    }

    /// <summary>
    /// Queries the DNS server for the specified record type.
    /// </summary>
    /// <param name="query">The query.</param>
    /// <param name="recordType">Type of the record.</param>
    /// <returns>Queries the DNS server for the specified record type of the result produced by this Task.</returns>
    public static Task<DnsQueryResult> QueryDnsAsync(String query, DnsRecordType recordType) => QueryDnsAsync(query, recordType, GetIPv4DnsServers().FirstOrDefault(), DnsDefaultPort);

    /// <summary>
    /// Gets the UTC time by querying from an NTP server.
    /// </summary>
    /// <param name="ntpServerAddress">The NTP server address.</param>
    /// <param name="port">The port.</param>
    /// <returns>The UTC time by querying from an NTP server of the result produced by this Task.</returns>
    public static async Task<DateTime> GetNetworkTimeUtcAsync(IPAddress ntpServerAddress, Int32 port = NtpDefaultPort) {
      if(ntpServerAddress == null) {
        throw new ArgumentNullException(nameof(ntpServerAddress));
      }

      // NTP message size - 16 bytes of the digest (RFC 2030)
      Byte[] ntpData = new Byte[48];

      // Setting the Leap Indicator, Version Number and Mode values
      ntpData[0] = 0x1B; // LI = 0 (no warning), VN = 3 (IPv4 only), Mode = 3 (Client Mode)

      // The UDP port number assigned to NTP is 123
      IPEndPoint endPoint = new IPEndPoint(ntpServerAddress, port);
      Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);


      await socket.ConnectAsync(endPoint).ConfigureAwait(false);


      socket.ReceiveTimeout = 3000; // Stops code hang if NTP is blocked
      _ = socket.Send(ntpData);
      _ = socket.Receive(ntpData);
      socket.Dispose();

      // Offset to get to the "Transmit Timestamp" field (time at which the reply 
      // departed the server for the client, in 64-bit timestamp format."
      const Byte serverReplyTime = 40;

      // Get the seconds part
      UInt64 intPart = BitConverter.ToUInt32(ntpData, serverReplyTime);

      // Get the seconds fraction
      UInt64 fractPart = BitConverter.ToUInt32(ntpData, serverReplyTime + 4);

      // Convert From big-endian to little-endian to match the platform
      if(BitConverter.IsLittleEndian) {
        intPart = intPart.SwapEndianness();
        fractPart = intPart.SwapEndianness();
      }

      UInt64 milliseconds = intPart * 1000 + fractPart * 1000 / 0x100000000L;

      // The time is given in UTC
      return new DateTime(1900, 1, 1, 0, 0, 0, DateTimeKind.Utc).AddMilliseconds((Int64)milliseconds);
    }

    /// <summary>
    /// Gets the UTC time by querying from an NTP server.
    /// </summary>
    /// <param name="ntpServerName">The NTP server, by default pool.ntp.org.</param>
    /// <param name="port">The port, by default NTP 123.</param>
    /// <returns>The UTC time by querying from an NTP server of the result produced by this Task.</returns>
    public static async Task<DateTime> GetNetworkTimeUtcAsync(String ntpServerName = "pool.ntp.org", Int32 port = NtpDefaultPort) {
      IPAddress[] addresses = await GetDnsHostEntryAsync(ntpServerName).ConfigureAwait(false);
      return await GetNetworkTimeUtcAsync(addresses.First(), port).ConfigureAwait(false);
    }

    #endregion*/
  }
}