func (h *EventHandler) getIndexOfSub(t interfaces.Topic, s interfaces.Subscriber) (int, error) {
subs, ok := h.subscriber[t.Topic()]
if !ok {
return -1, errors.New("Topic does not exist.")
}
for k, sub := range subs {
if s == sub {
return k, nil
}
}
return -1, errors.New("Subscriber not found.")
}
// Publish sends out a notification to all subscribers that have a subscription for the given topic.
func (h *EventHandler) Publish(t interfaces.Topic, p interfaces.Publisher) {
if t.Topic() == interfaces.AllTopics {
h.publishAll(t, p)
return
}
// Publish to normal topic subscribers
subs, ok := h.subscriber[t.Topic()]
if ok {
for _, sub := range subs {
sub.Notify(t, p)
}
}
// Publish to all topic subscribers
subs, _ = h.subscriber[interfaces.AllTopics]
for _, sub := range subs {
sub.Notify(t, p)
}
}
// Subscribe subscribes a struct that implements the Subscriber interface to a topic.
// The Subscriber's Notify method is called when the Publish method is called on the same topic.
// Returns an error if the same Subscriber already has a subscribtion for the given topic.
// Be aware, that subscribing to all topics does not revoke previous subscriptions.
func (h *EventHandler) Subscribe(t interfaces.Topic, s interfaces.Subscriber) error {
h.Lock()
defer h.Unlock()
// Check if topic exists. If not, create entry with new slice
_, ok := h.subscriber[t.Topic()]
if !ok {
h.subscriber[t.Topic()] = []interfaces.Subscriber{s}
return nil
}
// Check if subscriber already has a subscription of that topic
_, err := h.getIndexOfSub(t, s)
if err == nil {
return fmt.Errorf("Subscriber %v has already a subscription for topic %v.", s, t)
}
// Add subscriber
h.subscriber[t.Topic()] = append(h.subscriber[t.Topic()], s)
return nil
}
// Unsubscribe unsubscribes a struct that implements the Subscriber interface from a topic.
// Returns an error if the given Subscriber does not have a subscription for the given topic.
func (h *EventHandler) Unsubscribe(t interfaces.Topic, s interfaces.Subscriber) error {
h.Lock()
defer h.Unlock()
// Check if subscriber exists
index, err := h.getIndexOfSub(t, s)
if err != nil {
return err
}
// Delete subscriber from slice
h.subscriber[t.Topic()], h.subscriber[t.Topic()][len(h.subscriber[t.Topic()])-1] = append(h.subscriber[t.Topic()][:index], h.subscriber[t.Topic()][index+1:]...), nil
return nil
}