package activator

// PrepareScheduledToken orders token preparation with this host's local fence.
// An admitted callback finishes before its fence is installed. Other hosts do
// not wait for its IO. The callback must not reenter preparation or fencing for
// the same host. This establishes neither wake nor durable maintenance authority.
func (a *Service) PrepareScheduledToken(host string, prepare func() (string, error)) (string, error) {
	if a == nil || prepare == nil {
		return "", ErrFenced
	}
	for {
		a.mu.Lock()
		if a.fences[host] != 0 {
			a.mu.Unlock()
			return "", ErrFenced
		}
		if pending := a.tokenPreparations[host]; pending != nil {
			a.mu.Unlock()
			<-pending
			continue
		}
		if a.tokenPreparations == nil {
			a.tokenPreparations = make(map[string]chan struct{})
		}
		done := make(chan struct{})
		a.tokenPreparations[host] = done
		a.mu.Unlock()
		defer func() {
			a.mu.Lock()
			delete(a.tokenPreparations, host)
			close(done)
			a.mu.Unlock()
		}()
		return prepare()
	}
}