using DnsClient;

using System;

using System.Collections.Generic;

using System.Linq;

using System.Net;

using System.Threading.Tasks;

using log4net;

namespace NETworkManager.Utilities;

public class DNSClient : SingletonBase<DNSClient>

{

private static readonly ILog Log = LogManager.GetLogger(typeof(DNSClient));

/// <summary>

/// Error message which is returned when the DNS client is not configured.

/// </summary>

private const string NotConfiguredMessage = "DNS client is not configured. Call Configure() first.";

/// <summary>

/// Hold the current instance of the LookupClient.

/// </summary>

private LookupClient _client;

/// <summary>

/// Indicates if the DNS client is configured.

/// </summary>

private bool _isConfigured;

/// <summary>

/// Store the current DNS settings.

/// </summary>

private DNSClientSettings _settings;

/// <summary>

/// Method to configure the DNS client.

/// </summary>

/// <param name="settings"></param>

public void Configure(DNSClientSettings settings)

{

_settings = settings;

Log.Debug("Configure - Configuring DNS client...");

if (_settings.UseCustomDNSServers)

{

Log.Debug("Configure - Using custom DNS servers...");

// Setup custom DNS servers

List<NameServer> servers = [];

foreach (var (server, port) in _settings.DNSServers)

{

Log.Debug($"Configure - Adding custom DNS server: {server}:{port}");

servers.Add(new IPEndPoint(IPAddress.Parse(server), port));

}

Log.Debug("Configure - Creating LookupClient with custom DNS servers...");

_client = new LookupClient(new LookupClientOptions(servers.ToArray()));

}

else

{

Log.Debug("Configure - Creating LookupClient with Windows default DNS servers...");

_client = new LookupClient();

}

Log.Debug("Configure - DNS client configured.");

_isConfigured = true;

}

/// <summary>

/// Method to update the (Windows) name servers of the DNS client

/// when they may have changed due to a network update.

/// </summary>

public void UpdateWindowsDNSSever()

{

Log.Debug("UpdateWindowsDNSSever - Recreating LookupClient with with Windows default DNS servers...");

_client = new LookupClient();

}

/// <summary>

/// Resolve an IPv4 address from a hostname or FQDN.

/// </summary>

/// <param name="query">Hostname or FQDN as string like "example.com".</param>

/// <returns><see cref="IPAddress" /> of the host.</returns>

public async Task<DNSClientResultIPAddress> ResolveAAsync(string query)

{

if (!_isConfigured)

throw new DNSClientNotConfiguredException(NotConfiguredMessage);

try

{

var result = await _client.QueryAsync(query, QueryType.A);

// Pass the error we got from the lookup client (dns server).

if (result.HasError)

return new DNSClientResultIPAddress(result.HasError, result.ErrorMessage, $"{result.NameServer}");

// Validate result because of https://github.com/BornToBeRoot/NETworkManager/issues/1934

var record = result.Answers.ARecords().FirstOrDefault();

return record != null

? new DNSClientResultIPAddress(record.Address, $"{result.NameServer}")

: new DNSClientResultIPAddress(true,

$"IP address for \"{query}\" could not be resolved and the DNS server did not return an error. Try to check your DNS server with: dig @{result.NameServer.Address} {query}",

$"{result.NameServer}");

}

catch (DnsResponseException ex)

{

return new DNSClientResultIPAddress(true, ex.Message);

}

catch (Exception ex)

{

Log.Error($"Error while resolving A record (Query string is \"{query}\".", ex);

return new DNSClientResultIPAddress(true, ex.Message);

}

}

/// <summary>

/// Resolve an IPv6 address from a hostname or FQDN.

/// </summary>

/// <param name="query">Hostname or FQDN as string like "example.com".</param>

/// <returns><see cref="IPAddress" /> of the host.</returns>

public async Task<DNSClientResultIPAddress> ResolveAaaaAsync(string query)

{

if (!_isConfigured)

throw new DNSClientNotConfiguredException(NotConfiguredMessage);

try

{

var result = await _client.QueryAsync(query, QueryType.AAAA);

// Pass the error we got from the lookup client (dns server).

if (result.HasError)

return new DNSClientResultIPAddress(result.HasError, result.ErrorMessage, $"{result.NameServer}");

// Validate result because of https://github.com/BornToBeRoot/NETworkManager/issues/1934

var record = result.Answers.AaaaRecords().FirstOrDefault();

return record != null

? new DNSClientResultIPAddress(record.Address, $"{result.NameServer}")

: new DNSClientResultIPAddress(true,

$"IP address for \"{query}\" could not be resolved and the DNS server did not return an error. Try to check your DNS server with: dig @{result.NameServer.Address} {query}",

$"{result.NameServer}");

}

catch (DnsResponseException ex)

{

return new DNSClientResultIPAddress(true, ex.Message);

}

catch (Exception ex)

{

Log.Error($"Error while resolving AAAA record (Query string is \"{query}\".", ex);

return new DNSClientResultIPAddress(true, ex.Message);

}

}

/// <summary>

/// Resolve a CNAME from a hostname or FQDN.

/// </summary>

/// <param name="query">Hostname or FQDN as string like "example.com".</param>

/// <returns>CNAME of the host.</returns>

public async Task<DNSClientResultString> ResolveCnameAsync(string query)

{

if (!_isConfigured)

throw new DNSClientNotConfiguredException(NotConfiguredMessage);

try

{

var result = await _client.QueryAsync(query, QueryType.CNAME);

// Pass the error we got from the lookup client (dns server).

if (result.HasError)

return new DNSClientResultString(result.HasError, result.ErrorMessage, $"{result.NameServer}");

// Validate result because of https://github.com/BornToBeRoot/NETworkManager/issues/1934

var record = result.Answers.CnameRecords().FirstOrDefault();

return record != null

? new DNSClientResultString(record.CanonicalName, $"{result.NameServer}")

: new DNSClientResultString(true,

$"CNAME for \"{query}\" could not be resolved and the DNS server did not return an error. Try to check your DNS server with: dig @{result.NameServer.Address} {query}",

$"{result.NameServer}");

}

catch (DnsResponseException ex)

{

return new DNSClientResultString(true, ex.Message);

}

catch (Exception ex)

{

Log.Error($"Error while resolving CNAME record (Query string is \"{query}\".", ex);

return new DNSClientResultString(true, ex.Message);

}

}

/// <summary>

/// Resolve a PTR for an IP address.

/// </summary>

/// <param name="ipAddress">IP address of the host.</param>

/// <returns>PTR domain name.</returns>

public async Task<DNSClientResultString> ResolvePtrAsync(IPAddress ipAddress)

{

if (!_isConfigured)

throw new DNSClientNotConfiguredException(NotConfiguredMessage);

try

{

var result = await _client.QueryReverseAsync(ipAddress);

// Pass the error we got from the lookup client (dns server).

if (result.HasError)

return new DNSClientResultString(result.HasError, result.ErrorMessage, $"{result.NameServer}");

// Validate result because of https://github.com/BornToBeRoot/NETworkManager/issues/1934

var record = result.Answers.PtrRecords().FirstOrDefault();

return record != null

? new DNSClientResultString(record.PtrDomainName, $"{result.NameServer}")

: new DNSClientResultString(true,

$"PTR for \"{ipAddress}\" could not be resolved and the DNS server did not return an error. Try to check your DNS server with: dig @{result.NameServer.Address} -x {ipAddress}",

$"{result.NameServer}");

}

catch (DnsResponseException ex)

{

return new DNSClientResultString(true, ex.Message);

}

catch (Exception ex)

{

Log.Error($"Error while resolving PTR record (IP address is \"{ipAddress}\".", ex);

return new DNSClientResultString(true, ex.Message);

}

}

}