package server import ( "log" "math/rand" "sync" "time" ) // topic represents a channel to which subscribers can subscribe, and publishers // can publish a message type topic struct { id string last time.Time subscribers map[int]subscriber mu sync.Mutex } // subscriber is a function that is called for every new message on a topic type subscriber func(msg *message) error // newTopic creates a new topic func newTopic(id string, last time.Time) *topic { return &topic{ id: id, last: last, subscribers: make(map[int]subscriber), } } func (t *topic) Subscribe(s subscriber) int { t.mu.Lock() defer t.mu.Unlock() subscriberID := rand.Int() t.subscribers[subscriberID] = s t.last = time.Now() return subscriberID } func (t *topic) Unsubscribe(id int) { t.mu.Lock() defer t.mu.Unlock() delete(t.subscribers, id) } func (t *topic) Publish(m *message) error { t.mu.Lock() defer t.mu.Unlock() t.last = time.Now() for _, s := range t.subscribers { if err := s(m); err != nil { log.Printf("error publishing message to subscriber") } } return nil } func (t *topic) Subscribers() int { t.mu.Lock() defer t.mu.Unlock() return len(t.subscribers) }