tomo/event/event.go

// Package event provides a system for broadcasting events to multiple event
// handlers.
package event

// A cookie is returned when you add an event handler so you can remove it
// later if you so choose.
type Cookie interface {
	// Close removes the event handler this cookie is for.
	Close ()
}

// Broadcaster manages event listeners.
type Broadcaster[L any] struct {
	lastID    int
	listeners map[int] L
}

// Connect adds a new listener to the broadcaster and returns a corresponding
// cookie.
func (broadcaster *Broadcaster[L]) Connect (listener L) Cookie {
	broadcaster.ensure()
	
	cookie := broadcaster.newCookie()
	broadcaster.listeners[cookie.id] = listener
	return cookie
}

// Listeners returns a map of all connected listeners.
func (broadcaster *Broadcaster[L]) Listeners () map[int] L {
	broadcaster.ensure()
	return broadcaster.listeners
}

func (broadcaster *Broadcaster[L]) newCookie () cookie[L] {
	broadcaster.lastID ++
	return cookie[L] {
		id:          broadcaster.lastID,
		broadcaster: broadcaster,
	}
}

func (broadcaster *Broadcaster[L]) ensure () {
	if broadcaster.listeners == nil {
		broadcaster.listeners = make(map[int] L)
	}
}

// NoCookie is a cookie that does nothing when closed.
type NoCookie struct { }
func (NoCookie) Close () { }

type cookie[L any] struct {
	id int
	broadcaster *Broadcaster[L]
}

func (cookie cookie[L]) Close () {
	delete(cookie.broadcaster.listeners, cookie.id)
}

// FuncBroadcaster is a broadcaster that manages functions with no arguments.
type FuncBroadcaster struct {
	Broadcaster[func ()]
}

// Broadcast calls all connected listener funcs.
func (broadcaster *FuncBroadcaster) Broadcast () {
	for _, listener := range broadcaster.Listeners() {
		listener()
	}
}

type multiCookie []Cookie

// MultiCookie creates a single cookie that, when closed, closes a list of other
// cookies.
func MultiCookie (cookies ...Cookie) Cookie {
	return multiCookie(cookies)
}

func (cookies multiCookie) Close () {
	for _, cookie := range cookies {
		cookie.Close()
	}
}