package dns

import (
	"math/rand"
	"strings"

	"github.com/miekg/dns"
)

const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"

// Generate a random string
// https://stackoverflow.com/a/31832326
func generate(length int) string {
	// Create byte array with length
	word := make([]byte, length)

	// Go through word
	for index := range word {
		// Set index to random letter
		word[index] = letterBytes[rand.Intn(len(letterBytes))]
	}

	return string(word)
}

// Query wildcard
func Wildcard(client *dns.Client, resolvers []string, domain string) bool {
	for {
		// Generate subdomain
		subdomain := generate(10) + "." + domain

		// Create message
		message := new(dns.Msg)

		// Set question
		message.SetQuestion(dns.Fqdn(subdomain), dns.TypeA)

		// Choose random resolver
		resolver := resolvers[rand.Intn(len(resolvers))]

		// Query response
		response, _, err := client.Exchange(message, resolver)
		if err != nil {
			// Ratelimited
			if strings.ContainsAny(err.Error(), "i/o timeout") {
				continue
			}

			return false
		}

		// Store status
		var status bool

		// Go through answers
		for _, answer := range response.Answer {
			// Map record
			_, status = answer.(*dns.A)
		}

		return status
	}
}