package cdns

import (
	"net"
	"os"
	"strings"
	"time"

	"github.com/miekg/dns"
)

// DNS check configuration constants.
const (
	// Timeout is the DNS query timeout in seconds.
	Timeout        float64 = float64(1.5)
	MaxTrials      uint    = 3
	MaxNameservers uint    = 20
	MaxAddresses   uint    = 10
	EdnsbufferSize uint16  = 4096
)

var (
	conf           *dns.ClientConfig
	debug          = false
	maxTrials      = 3
	v4only         = true
	v6only         = false
	bufsize        = EdnsbufferSize
	timeout        = time.Duration(float64(Timeout) * float64(time.Second))
	noedns         = false
	recursion      = false
	tcp            = false
	noauthrequired = false
	nodnssec       = false
)

func init() {
	conf = &dns.ClientConfig{
		Servers: resolversFromEnv(),
		Port:    "53",
	}
}

func resolversFromEnv() []string {
	const defaults = "188.93.17.19,188.93.16.19,82.117.245.122"
	resolvers := strings.Split(os.Getenv("RSMON_DNS_RESOLVERS"), ",")
	if strings.TrimSpace(os.Getenv("RSMON_DNS_RESOLVERS")) == "" {
		resolvers = strings.Split(defaults, ",")
	}

	valid := make([]string, 0, len(resolvers))
	for _, resolver := range resolvers {
		resolver = strings.TrimSpace(resolver)
		if net.ParseIP(resolver) != nil {
			valid = append(valid, resolver)
		}
	}
	if len(valid) == 0 {
		return strings.Split(defaults, ",")
	}
	return valid
}