package events

import (
	"log"
	"sync"

	"golang.org/x/exp/slices"
)

type ListenerFunc func(interface{})

type Listener struct {
	Event  string
	Handle ListenerFunc
}

type EventBus struct {
	lock      sync.RWMutex
	listeners map[string][]*Listener
}

func NewEventBus() *EventBus {
	return &EventBus{
		listeners: map[string][]*Listener{},
	}
}

// Subscribe a listener for the given event type
func (eb *EventBus) Subscribe(event string, f ListenerFunc) *Listener {
	eb.lock.Lock()
	defer eb.lock.Unlock()

	log.Printf("[EventBus] Subscribed listener for %q", event)

	l := &Listener{event, f}

	if prev, found := eb.listeners[event]; !found {
		eb.listeners[event] = []*Listener{l}
	} else {
		eb.listeners[event] = append(prev, l)
	}

	return l
}

// Unsubscribe removes a listener for the given event type
func (eb *EventBus) Unsubscribe(l *Listener) {
	eb.lock.Lock()
	defer eb.lock.Unlock()

	listeners := eb.listeners[l.Event]

	i := slices.Index(listeners, l)
	if i >= 0 {
		// TODO: Magari usare la tecnica di spostare l'ultimo alla posizione dell'elemento rimosso e accorciare lo slice, tanto alla fine l'ordine dei listener non conta veramente
		eb.listeners[l.Event] = append(listeners[:i], listeners[i+1:]...)
	}
}

// Dispatch
func (eb *EventBus) Dispatch(event string, data interface{}) {
	eb.lock.RLock()
	defer eb.lock.RUnlock()

	log.Printf("[EventBus] Fired event %q with value %v", event, data)

	if listeners, found := eb.listeners[event]; found {
		// make a copy of "listeners" to pass to the goroutine and not block the dispatcher thread
		tmpListeners := append([]*Listener{}, listeners...)
		go func() {
			for _, listener := range tmpListeners {
				listener.Handle(data)
			}
		}()
	}
}