feat(cache): implement TTLCache and TimeCache (#1822)

* feat(pkg): implement ttlcache and timecache

pkg/timecache/timecache.go

@@ -0,0 +1,74 @@
+package timecache
+
+import (
+	"sync"
+	"time"
+)
+
+type Cache struct {
+	m sync.RWMutex
+	t time.Time
+	o Options
+}
+
+type Options struct {
+	round time.Duration
+}
+
+func New(o Options) *Cache {
+	c := Cache{
+		o: o,
+	}
+
+	return &c
+}
+
+func (t *Cache) Now() time.Time {
+	t.m.RLock()
+	if !t.t.IsZero() {
+		defer t.m.RUnlock()
+		return t.t
+	}
+
+	t.m.RUnlock()
+	return t.update()
+}
+
+func (t *Cache) update() time.Time {
+	t.m.Lock()
+	defer t.m.Unlock()
+	if !t.t.IsZero() {
+		return t.t
+	}
+
+	var d time.Duration
+	if t.o.round > time.Nanosecond {
+		d = t.o.round
+	} else {
+		d = time.Second * 1
+	}
+
+	t.t = time.Now().Round(d)
+
+	go func(duration time.Duration) {
+		if t.o.round > time.Nanosecond {
+			duration = t.o.round / 2
+		}
+
+		time.Sleep(duration)
+		t.reset()
+	}(d)
+
+	return t.t
+}
+
+func (t *Cache) reset() {
+	t.m.Lock()
+	defer t.m.Unlock()
+	t.t = time.Time{}
+}
+
+func (o Options) Round(d time.Duration) Options {
+	o.round = d
+	return o
+}