package server

import (
	"context"
	"fmt"
	"strings"
)

// DNSProvider manages the TXT records ACME DNS-01 challenges need.
type DNSProvider interface {
	// CreateTXT adds a TXT record with the given value at name.
	CreateTXT(ctx context.Context, name, value string) error
	// DeleteTXT removes every TXT record at name (best effort cleanup).
	DeleteTXT(ctx context.Context, name string) error
}

// challengeRecordName is the TXT record name a hostname's DNS-01 challenge
// lives at; the wildcard of a hostname shares the same record.
func challengeRecordName(hostname string) string {
	return "_acme-challenge." + hostname
}

// relativeRecordName strips the zone suffix from a record name, as DNS
// provider APIs expect names relative to the zone.
func relativeRecordName(name, zone string) (string, error) {
	suffix := "." + zone
	if !strings.HasSuffix(name, suffix) {
		return "", fmt.Errorf("record %q is not under zone %q", name, zone)
	}
	return strings.TrimSuffix(name, suffix), nil
}

// dnsZone guesses the registrable zone that hosts the tunnel hostnames:
// the domain minus its first label when it has three or more (tunnel.tzgyn.dev
// is served by the tzgyn.dev zone). Override with DNS_ZONE when wrong.
func DNSZone(domain string) string {
	labels := strings.Split(domain, ".")
	if len(labels) >= 3 {
		return strings.Join(labels[1:], ".")
	}
	return domain
}