package calendar

import "sync"

type ChatEventHub struct {
	mu          sync.Mutex
	subscribers map[string]map[chan struct{}]struct{}
}

func NewChatEventHub() *ChatEventHub {
	return &ChatEventHub{
		subscribers: map[string]map[chan struct{}]struct{}{},
	}
}

func (h *ChatEventHub) Subscribe(itemID string, channel string) (chan struct{}, func()) {
	key := chatEventKey(itemID, channel)
	events := make(chan struct{}, 1)

	h.mu.Lock()
	if h.subscribers[key] == nil {
		h.subscribers[key] = map[chan struct{}]struct{}{}
	}
	h.subscribers[key][events] = struct{}{}
	h.mu.Unlock()

	return events, func() {
		h.mu.Lock()
		defer h.mu.Unlock()

		delete(h.subscribers[key], events)
		if len(h.subscribers[key]) == 0 {
			delete(h.subscribers, key)
		}
		close(events)
	}
}

func (h *ChatEventHub) Publish(itemID string, channel string) {
	key := chatEventKey(itemID, channel)

	h.mu.Lock()
	defer h.mu.Unlock()

	for events := range h.subscribers[key] {
		select {
		case events <- struct{}{}:
		default:
		}
	}
}

func chatEventKey(itemID string, channel string) string {
	return itemID + ":" + channel
}