package hostname

import (
	"errors"
	"fmt"
	"net"
	"strings"
)

var ErrorEmptyDomainName error = errors.New("domain name is empty")
var ErrorDomainNameMisconfigured error = errors.New("your OS domain name is not configured correctly")

// returns 'hostname', 'domainname'
func Split(s string) (string, string) {
	parts := strings.Fields(s)
	if len(parts) == 0 {
		return "", ""
	}
	if len(parts) == 1 {
		return parts[0], ""
	}
	return parts[0], strings.Join(parts[1:], ".")
}

// checks to make sure there is a domainname
func ValidDomainname(s string) error {
	_, domainname := Split(s)
	if domainname == "" {
		return ErrorEmptyDomainName
	}
	return nil
}

func ReverseLookupFQDN(hostname string) (string, error) {
	addrs, err := net.LookupIP(hostname)
	if err != nil || len(addrs) == 0 {
		return hostname, fmt.Errorf("failed to lookup IP for hostname %s: %w", hostname, err)
	}

	// Try reverse lookup on the first IP address
	names, err := net.LookupAddr(addrs[0].String())
	if err != nil || len(names) == 0 {
		return hostname, fmt.Errorf("reverse DNS lookup failed for IP %s: %w", addrs[0].String(), err)
	}

	return names[0], nil
}