// Package hedns implements the Hurricane Electric dynamic DNS update protocol.
package hedns

import (
	"fmt"
	"io"
	"net"
	"net/http"
	"net/url"
	"strings"
	"time"
)

const (
	updateURL      = "https://dyn.dns.he.net/nic/update"
	requestTimeout = 15 * time.Second
)

// Update pushes a single hostname -> ip mapping. HE picks the A or AAAA
// record based on the family of ip.
func Update(hostname, token string, ip net.IP) error {
	client := http.Client{Timeout: requestTimeout}

	form := url.Values{
		"hostname": {hostname},
		"password": {token},
		"myip":     {ip.String()},
	}

	resp, err := client.PostForm(updateURL, form)
	if err != nil {
		return fmt.Errorf("updating %s: %w", hostname, err)
	}
	defer resp.Body.Close()

	body, err := io.ReadAll(io.LimitReader(resp.Body, 4096))
	if err != nil {
		return fmt.Errorf("updating %s: reading response: %w", hostname, err)
	}

	return interpretResponse(hostname, strings.TrimSpace(string(body)))
}

func interpretResponse(hostname, body string) error {
	switch {
	case strings.HasPrefix(body, "good"), strings.HasPrefix(body, "nochg"):
		return nil
	case body == "badauth":
		return fmt.Errorf("updating %s: authentication failed (bad hostname/token)", hostname)
	case body == "nohost":
		return fmt.Errorf("updating %s: hostname not found on account", hostname)
	case body == "notfqdn":
		return fmt.Errorf("updating %s: hostname is not a valid fully-qualified domain name", hostname)
	case body == "abuse":
		return fmt.Errorf("updating %s: blocked for abuse", hostname)
	case body == "":
		return fmt.Errorf("updating %s: empty response from server", hostname)
	default:
		return fmt.Errorf("updating %s: unexpected response %q", hostname, body)
	}
}