using System;
using System.Collections.Generic;
using System.Linq;
#nullable enable
using System.Net;
using System.Threading.Tasks;

namespace Swan.Net.Dns {
  /// <summary>
  /// DnsClient public methods.
  /// </summary>
  internal partial class DnsClient {
    private readonly IPEndPoint _dns;
    private readonly IDnsRequestResolver _resolver;

    public DnsClient(IPEndPoint dns, IDnsRequestResolver? resolver = null) {
      this._dns = dns;
      this._resolver = resolver ?? new DnsUdpRequestResolver(new DnsTcpRequestResolver());
    }

    public DnsClient(IPAddress ip, Int32 port = Network.DnsDefaultPort, IDnsRequestResolver? resolver = null) : this(new IPEndPoint(ip, port), resolver) {
    }

    public DnsClientRequest Create(IDnsRequest? request = null) => new DnsClientRequest(this._dns, request, this._resolver);

    public async Task<IList<IPAddress>> Lookup(String domain, DnsRecordType type = DnsRecordType.A) {
      if(String.IsNullOrWhiteSpace(domain)) {
        throw new ArgumentNullException(nameof(domain));
      }

      if(type != DnsRecordType.A && type != DnsRecordType.AAAA) {
        throw new ArgumentException("Invalid record type " + type);
      }

      DnsClientResponse response = await this.Resolve(domain, type).ConfigureAwait(false);
      List<IPAddress> ips = response.AnswerRecords.Where(r => r.Type == type).Cast<DnsIPAddressResourceRecord>().Select(r => r.IPAddress).ToList();

      return ips.Count == 0 ? throw new DnsQueryException(response, "No matching records") : ips;
    }

    public async Task<String> Reverse(IPAddress ip) {
      if(ip == null) {
        throw new ArgumentNullException(nameof(ip));
      }

      DnsClientResponse response = await this.Resolve(DnsDomain.PointerName(ip), DnsRecordType.PTR);
      IDnsResourceRecord ptr = response.AnswerRecords.FirstOrDefault(r => r.Type == DnsRecordType.PTR);

      return ptr == null ? throw new DnsQueryException(response, "No matching records") : ((DnsPointerResourceRecord)ptr).PointerDomainName.ToString();
    }

    public Task<DnsClientResponse> Resolve(String domain, DnsRecordType type) => this.Resolve(new DnsDomain(domain), type);

    public Task<DnsClientResponse> Resolve(DnsDomain domain, DnsRecordType type) {
      DnsClientRequest request = this.Create();
      DnsQuestion question = new DnsQuestion(domain, type);

      request.Questions.Add(question);
      request.OperationCode = DnsOperationCode.Query;
      request.RecursionDesired = true;

      return request.Resolve();
    }
  }
}