package app

import "sync"

// Topic is a generic pub/sub for broadcasting updates.
type Topic[T any] struct {
	c  []chan *T
	mu sync.Mutex
}

// Watch subscribes a channel to receive updates.
func (t *Topic[T]) Watch(c chan *T) {
	t.mu.Lock()
	defer t.mu.Unlock()
	t.c = append(t.c, c)
}

// Send broadcasts to all subscribers. If a subscriber's channel is full,
// the message is dropped for that subscriber only; the subscriber is not
// removed, so the connection stays alive and later updates are still delivered.
func (t *Topic[T]) Send(b *T) {
	t.mu.Lock()
	defer t.mu.Unlock()
	for i := 0; i < len(t.c); i++ {
		select {
		case t.c[i] <- b:
		default:
			// Channel full: drop this message for this subscriber, keep them subscribed
		}
	}
}

// Close closes all subscriber channels.
func (t *Topic[T]) Close() {
	t.mu.Lock()
	defer t.mu.Unlock()
	for _, c := range t.c {
		close(c)
	}
	t.c = t.c[:0]
}

// Merge represents a map merge event (two maps becoming one).
type Merge struct {
	From, To int
	Shift    Coord
}