package web

import "sync"

// Broadcaster fans a string message out to all SSE subscribers. Slow
// subscribers drop messages rather than blocking publishers.
type Broadcaster struct {
	mu   sync.Mutex
	subs map[chan string]struct{}
}

func NewBroadcaster() *Broadcaster {
	return &Broadcaster{subs: make(map[chan string]struct{})}
}

func (b *Broadcaster) Subscribe() chan string {
	ch := make(chan string, 8)
	b.mu.Lock()
	b.subs[ch] = struct{}{}
	b.mu.Unlock()
	return ch
}

func (b *Broadcaster) Unsubscribe(ch chan string) {
	b.mu.Lock()
	if _, ok := b.subs[ch]; ok {
		delete(b.subs, ch)
		close(ch)
	}
	b.mu.Unlock()
}

func (b *Broadcaster) Publish(msg string) {
	b.mu.Lock()
	defer b.mu.Unlock()
	for ch := range b.subs {
		select {
		case ch <- msg:
		default: // drop for slow subscriber
		}
	}
}