Add events implementation

It allows us to have unified way to propagate state changes across an app

Co-Authored-By: Christophe Fergeau <cfergeau@redhat.com>
Signed-off-by: Yevhen Vydolob <yvydolob@redhat.com>

Author: evidolob

pkg/events/emitter.go

@@ -0,0 +1,46 @@
+package events
+
+import (
+	"sync"
+)
+
+type Event[T any] interface {
+	AddListener(listener Notifiable[T])
+	RemoveListener(listener Notifiable[T])
+	Fire(data T)
+}
+
+type Notifiable[T any] interface {
+	Notify(event T)
+}
+
+type event[T any] struct {
+	listeners  map[Notifiable[T]]Notifiable[T]
+	eventMutex sync.Mutex
+}
+
+func NewEvent[T any]() Event[T] {
+	return &event[T]{
+		listeners: make(map[Notifiable[T]]Notifiable[T]),
+	}
+}
+
+func (e *event[T]) AddListener(listener Notifiable[T]) {
+	e.eventMutex.Lock()
+	defer e.eventMutex.Unlock()
+	e.listeners[listener] = listener
+}
+
+func (e *event[T]) RemoveListener(listener Notifiable[T]) {
+	e.eventMutex.Lock()
+	defer e.eventMutex.Unlock()
+	delete(e.listeners, listener)
+}
+
+func (e *event[T]) Fire(event T) {
+	e.eventMutex.Lock()
+	defer e.eventMutex.Unlock()
+	for _, listener := range e.listeners {
+		go listener.Notify(event)
+	}
+}

pkg/events/emitter_test.go

@@ -0,0 +1,41 @@
+package events
+
+import (
+	"sync"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+type TestEventData struct {
+	Foo string
+}
+
+type eventListener struct {
+	notifyCb func(e TestEventData)
+}
+
+func newEventListener(notifyCb func(e TestEventData)) *eventListener {
+	return &eventListener{notifyCb: notifyCb}
+}
+
+func (listener *eventListener) Notify(e TestEventData) {
+	listener.notifyCb(e)
+}
+
+func TestEmitter(t *testing.T) {
+	var wg sync.WaitGroup
+	wg.Add(1)
+	var data string
+
+	event := NewEvent[TestEventData]()
+	event.AddListener(newEventListener(func(e TestEventData) {
+		data = e.Foo
+		wg.Done()
+	}))
+	event.Fire(TestEventData{Foo: "bar"})
+
+	wg.Wait()
+
+	assert.Equal(t, "bar", data)
+}