From df1be55debeece9292087fa947905c9864f4c700 Mon Sep 17 00:00:00 2001
From: Roman <roman.atachiants@gmail.com>
Date: Sun, 8 Oct 2023 13:13:29 +0400
Subject: [PATCH] Add OnEvery timer event

---
 emit/event.go      | 32 ++++++++++++++++++++++++++++++++
 emit/event_test.go | 23 +++++++++++++++++++++++
 2 files changed, 55 insertions(+)

diff --git a/emit/event.go b/emit/event.go
index 22c98ae..a5d4bee 100644
--- a/emit/event.go
+++ b/emit/event.go
@@ -6,6 +6,7 @@ package emit
 import (
 	"context"
 	"math"
+	"sync/atomic"
 	"time"
 
 	"github.com/kelindar/event"
@@ -46,6 +47,20 @@ func (e fault) Type() uint32 {
 	return math.MaxUint32
 }
 
+// ----------------------------------------- Timer Event -----------------------------------------
+
+var nextTimerID uint32 = 1 << 30
+
+// timer represents a timer event
+type timer struct {
+	ID uint32
+}
+
+// Type returns the type of the event
+func (e timer) Type() uint32 {
+	return e.ID
+}
+
 // ----------------------------------------- Subscribe -----------------------------------------
 
 // On subscribes to an event, the type of the event will be automatically
@@ -74,6 +89,23 @@ func OnError(handler func(err error, about any)) context.CancelFunc {
 	})
 }
 
+// OnEvery creates a timer that fires every 'interval' and calls the handler.
+func OnEvery(handler func(now time.Time, elapsed time.Duration) error, interval time.Duration) context.CancelFunc {
+	id := atomic.AddUint32(&nextTimerID, 1)
+	if id >= (math.MaxUint32 - 1) {
+		panic("emit: too many timers created")
+	}
+
+	// Subscribe to the timer event
+	cancel := OnType[timer](id, func(_ timer, now time.Time, elapsed time.Duration) error {
+		return handler(now, elapsed)
+	})
+
+	// Start the timer
+	Every(timer{ID: id}, interval)
+	return cancel
+}
+
 // ----------------------------------------- Publish -----------------------------------------
 
 // Next writes an event during the next tick.
diff --git a/emit/event_test.go b/emit/event_test.go
index fc707a1..1b7f6ab 100644
--- a/emit/event_test.go
+++ b/emit/event_test.go
@@ -2,6 +2,7 @@ package emit
 
 import (
 	"fmt"
+	"math"
 	"sync/atomic"
 	"testing"
 	"time"
@@ -125,6 +126,28 @@ func TestOnTypeError(t *testing.T) {
 	assert.Equal(t, "OnType()", (<-errors).Error())
 }
 
+func TestOnEvery(t *testing.T) {
+	events := make(chan MyEvent2)
+	defer OnEvery(func(now time.Time, elapsed time.Duration) error {
+		events <- MyEvent2{}
+		return nil
+	}, 20*time.Millisecond)()
+
+	// Emit the event
+	<-events
+	<-events
+	<-events
+}
+
+func TestTooManyTimers(t *testing.T) {
+	assert.Panics(t, func() {
+		nextTimerID = math.MaxUint32 - 1
+		defer OnEvery(func(now time.Time, elapsed time.Duration) error {
+			return nil
+		}, 200*time.Millisecond)()
+	})
+}
+
 // ------------------------------------- Test Events -------------------------------------
 
 const (