package notify

import "sync"

// Subscriber represents a client subscribed to receive notifications.
// Each subscriber has a unique ID and receives notifications through
// a buffered channel. Subscribers are created via Notifier.Subscribe().
type Subscriber struct {
	// ID is the unique identifier for this subscriber.
	// This is automatically generated using cryptographic random bytes.
	ID Target

	// notifications is the buffered channel for receiving notifications.
	// The buffer size is determined by the Notifier's configuration.
	notifications chan Notification

	// notifier is a reference back to the parent Notifier.
	notifier *Notifier

	// unsubscribelock protects the unsubscribe operation.
	unsubscribelock *sync.Mutex

	// unsubscribed tracks whether this subscriber has been unsubscribed.
	unsubscribed bool
}

// Listen returns a receive-only channel for reading notifications.
// Use this channel in a for-range loop to process notifications:
//
//	for notification := range sub.Listen() {
//	    // Process notification
//	    fmt.Println(notification.Message)
//	}
//
// The channel will be closed when the subscriber unsubscribes or
// when the notifier is closed.
func (s *Subscriber) Listen() <-chan Notification {
	return s.notifications
}

// Unsubscribe removes this subscriber from the notifier and closes the notification channel.
// It is safe to call Unsubscribe multiple times; subsequent calls are no-ops.
// After unsubscribe, the channel returned by Listen() will be closed immediately.
// Any goroutines reading from Listen() will detect the closure and can exit gracefully.
func (s *Subscriber) Unsubscribe() {
	s.unsubscribelock.Lock()
	if s.unsubscribed {
		s.unsubscribelock.Unlock()
		return
	}
	s.unsubscribed = true
	s.unsubscribelock.Unlock()

	s.notifier.RemoveSubscriber(s)
}