enhance cache functionality with stale time and background refresh support

relay/cache/cache.go

@@ -8,11 +8,13 @@ import (
 type item struct {
 	value      interface{}
 	expiration int64
+	staleTime  int64
 }
 
 type Cache struct {
-	items map[string]item
+	items      map[string]item
-	mu    sync.RWMutex
+	mu         sync.RWMutex
+	refreshing sync.Map
 }
 
 func New() *Cache {
@@ -27,35 +29,68 @@ func (c *Cache) Set(key string, value interface{}, duration time.Duration) {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 
+	now := time.Now().UnixNano()
 	c.items[key] = item{
 		value:      value,
-		expiration: time.Now().Add(duration).UnixNano(),
+		expiration: now + duration.Nanoseconds(),
+		staleTime:  now + (duration * 2).Nanoseconds(), // Stale time is double the normal duration
 	}
 }
 
 func (c *Cache) Get(key string) (interface{}, bool) {
 	c.mu.RLock()
-	defer c.mu.RUnlock()
-
 	item, exists := c.items[key]
+	c.mu.RUnlock()
+
 	if !exists {
 		return nil, false
 	}
 
-	if time.Now().UnixNano() > item.expiration {
+	now := time.Now().UnixNano()
+	if now > item.staleTime {
 		return nil, false
 	}
 
 	return item.value, true
 }
 
+func (c *Cache) GetOrRefresh(key string, refreshFn func() (interface{}, error), duration time.Duration) (interface{}, bool) {
+	// Try to get from cache first
+	if value, exists := c.Get(key); exists {
+		now := time.Now().UnixNano()
+		item := c.items[key]
+
+		// If the value is expired but not stale, trigger refresh in background
+		if now > item.expiration && now <= item.staleTime {
+			if _, loading := c.refreshing.LoadOrStore(key, true); !loading {
+				go func() {
+					defer c.refreshing.Delete(key)
+					if newValue, err := refreshFn(); err == nil {
+						c.Set(key, newValue, duration)
+					}
+				}()
+			}
+		}
+		return value, true
+	}
+
+	// If no value exists, do a blocking refresh
+	value, err := refreshFn()
+	if err != nil {
+		return nil, false
+	}
+
+	c.Set(key, value, duration)
+	return value, true
+}
+
 func (c *Cache) startCleanup() {
 	ticker := time.NewTicker(time.Minute)
 	for range ticker.C {
 		c.mu.Lock()
 		now := time.Now().UnixNano()
 		for k, v := range c.items {
-			if now > v.expiration {
+			if now > v.staleTime {
 				delete(c.items, k)
 			}
 		}

relay/trending/kinds.go

@@ -23,12 +23,7 @@ var (
 	cacheDuration = 5 * time.Minute
 )
 
-// GetTrendingKind20 returns the top 20 trending posts of kind 20 from the last 24 hours
+func fetchTrendingKind20(db *sql.DB) ([]Post, error) {
-func GetTrendingKind20(db *sql.DB) ([]Post, error) {
-	if cached, ok := trendingCache.Get("trending_kind_20"); ok {
-		return cached.([]Post), nil
-	}
-
 	query := `
 		WITH reactions AS (
 			SELECT 
@@ -76,6 +71,17 @@ func GetTrendingKind20(db *sql.DB) ([]Post, error) {
 		trendingPosts = append(trendingPosts, post)
 	}
 
-	trendingCache.Set("trending_kind_20", trendingPosts, cacheDuration)
 	return trendingPosts, nil
 }
+
+func GetTrendingKind20(db *sql.DB) ([]Post, error) {
+	posts, exists := trendingCache.GetOrRefresh("trending_kind_20", func() (interface{}, error) {
+		return fetchTrendingKind20(db)
+	}, cacheDuration)
+
+	if !exists {
+		return nil, nil
+	}
+
+	return posts.([]Post), nil
+}