// update function, making it ready for use.
func NewFromFunc[T any](ttl time.Duration, opts Opts, update func() (T, error)) *Cache[T] {
	return &Cache[T]{
		ttl:      ttl,
		updateFn: update,
		opts:     opts,
	}
}

// InitOnce initializes the cache with a TTL and an update function. It is
// guaranteed to be called only once.
func (t *Cache[T]) InitOnce(ttl time.Duration, opts Opts, update func() (T, error)) {
	t.Once.Do(func() {

	}
}

func saveKeyEtcdWithTTL(ctx context.Context, client *etcd.Client, key string, data []byte, ttl int64) error {
	timeoutCtx, cancel := context.WithTimeout(ctx, defaultContextTimeout)
	defer cancel()
	lease, err := client.Grant(timeoutCtx, ttl)
	if err != nil {
		return etcdErrToErr(err, client.Endpoints())
	}
	_, err = client.Put(timeoutCtx, key, string(data), etcd.WithLease(lease.ID))

const etcdPathSeparator = "/"

// create a new coredns service record for the bucket.
func newCoreDNSMsg(ip string, port string, ttl uint32, t time.Time) ([]byte, error) {
	return json.Marshal(&SrvRecord{
		Host:         ip,
		Port:         json.Number(port),
		TTL:          ttl,
		CreationDate: t,
	})
}

// Close closes the internal etcd client and cannot be used further
func (c *CoreDNS) Close() error {

	Weight   int         `json:"weight,omitempty"`
	Text     string      `json:"text,omitempty"`
	Mail     bool        `json:"mail,omitempty"` // Be an MX record. Priority becomes Preference.
	TTL      uint32      `json:"ttl,omitempty"`

	// Holds info about when the entry was created first.
	CreationDate time.Time `json:"creationDate"`

	// When a SRV record with a "Host: IP-address" is added, we synthesize