package dnsresolver

import (
	"errors"
	"net"

	"github.com/miekg/dns"
)

type dnsResolver struct {
	resolver dns.Client
}

// New creates new DomainNameResolver.
func New() DomainNameResolver {
	return &dnsResolver{
		resolver: dns.Client{},
	}
}

// ResolveA implements DomainNameResolver.
func (r *dnsResolver) ResolveA(domain, nameserver string) ([]net.IP, error) {
	msg := &dns.Msg{}
	msg.SetQuestion(domain+".", dns.TypeA)

	answer, _, err := r.resolver.Exchange(msg, nameserver+":53")
	if err != nil {
		return nil, err
	}

	if len(answer.Answer) == 0 {
		return nil, errors.New("empty answer")
	}

	result := make([]net.IP, len(answer.Answer))
	for idx, rr := range answer.Answer {
		record := rr.(*dns.A)
		result[idx] = record.A
	}
	return result, nil
}

var (
	_ DomainNameResolver = &dnsResolver{}
)