feat: cache top-picks with stale-while-refresh

internal/anime/recommendations.go

@@ -4,12 +4,133 @@ import (
 	"context"
 	"mal/internal/anime/recommendations"
 	"mal/internal/domain"
+	"mal/internal/observability"
+	"strings"
+	"sync"
+	"time"
 )
 
-func (s *animeService) GetTopPickForYou(ctx context.Context, userID string) (domain.CatalogSectionData, error) {
-	return recommendations.GetTopPicksForYou(ctx, s.jikan, s.repo, userID, recommendations.TopPickLimit)
+type recommendationComputeFunc func(context.Context, string, int) (domain.CatalogSectionData, error)
+
+type topPicksCacheKey struct {
+	userID string
+	limit  int
 }
 
-func (s *animeService) GetTopPicksForYou(ctx context.Context, userID string) (domain.CatalogSectionData, error) {
-	return recommendations.GetTopPicksForYou(ctx, s.jikan, s.repo, userID, recommendations.TopPicksLimit)
+type topPicksCacheEntry struct {
+	data       domain.CatalogSectionData
+	updatedAt  time.Time
+	hasData    bool
+	refreshing bool
+}
+
+type topPicksCache struct {
+	mu      sync.Mutex
+	entries map[topPicksCacheKey]*topPicksCacheEntry
+}
+
+const topPicksRefreshTimeout = 30 * time.Second
+
+func (s *animeService) GetTopPickForYou(_ context.Context, userID string) (domain.CatalogSectionData, error) {
+	return s.getCachedTopPicksForYou(userID, recommendations.TopPickLimit), nil
+}
+
+func (s *animeService) GetTopPicksForYou(_ context.Context, userID string) (domain.CatalogSectionData, error) {
+	return s.getCachedTopPicksForYou(userID, recommendations.TopPicksLimit), nil
+}
+
+func (s *animeService) fetchTopPicksForYou(ctx context.Context, userID string, limit int) (domain.CatalogSectionData, error) {
+	return recommendations.GetTopPicksForYou(ctx, s.jikan, s.repo, userID, limit)
+}
+
+func (s *animeService) getCachedTopPicksForYou(userID string, limit int) domain.CatalogSectionData {
+	userID = strings.TrimSpace(userID)
+	if userID == "" {
+		return domain.CatalogSectionData{Animes: []domain.Anime{}}
+	}
+
+	key := topPicksCacheKey{userID: userID, limit: limit}
+	now := time.Now()
+
+	s.topPicksCache.mu.Lock()
+	entry := s.topPicksCache.entries[key]
+	if entry != nil && entry.hasData {
+		data := cloneCatalogSectionData(entry.data)
+		if now.Sub(entry.updatedAt) >= s.topPicksCacheTTL && !entry.refreshing {
+			entry.refreshing = true
+			go s.refreshTopPicksForYou(key)
+		}
+		s.topPicksCache.mu.Unlock()
+		return data
+	}
+
+	if entry == nil {
+		entry = &topPicksCacheEntry{}
+		s.topPicksCache.entries[key] = entry
+	}
+	if !entry.refreshing {
+		entry.refreshing = true
+		go s.refreshTopPicksForYou(key)
+	}
+	s.topPicksCache.mu.Unlock()
+
+	return domain.CatalogSectionData{Animes: []domain.Anime{}}
+}
+
+func (s *animeService) refreshTopPicksForYou(key topPicksCacheKey) {
+	ctx, cancel := context.WithTimeout(context.Background(), topPicksRefreshTimeout)
+	defer cancel()
+
+	data, err := s.computeTopPicks(ctx, key.userID, key.limit)
+	if err != nil {
+		observability.WarnContext(ctx,
+			"top_picks_refresh_failed",
+			"anime",
+			"",
+			map[string]any{"user_id": key.userID, "limit": key.limit},
+			err,
+		)
+		s.topPicksCache.mu.Lock()
+		if entry := s.topPicksCache.entries[key]; entry != nil {
+			entry.refreshing = false
+		}
+		s.topPicksCache.mu.Unlock()
+		return
+	}
+
+	s.topPicksCache.mu.Lock()
+	s.topPicksCache.entries[key] = &topPicksCacheEntry{
+		data:      cloneCatalogSectionData(data),
+		updatedAt: time.Now(),
+		hasData:   true,
+	}
+	s.topPicksCache.mu.Unlock()
+}
+
+func (s *animeService) InvalidateTopPicksForUser(userID string) {
+	userID = strings.TrimSpace(userID)
+	if userID == "" {
+		return
+	}
+
+	s.topPicksCache.mu.Lock()
+	defer s.topPicksCache.mu.Unlock()
+	for key := range s.topPicksCache.entries {
+		if key.userID == userID {
+			delete(s.topPicksCache.entries, key)
+		}
+	}
+}
+
+func cloneCatalogSectionData(data domain.CatalogSectionData) domain.CatalogSectionData {
+	data.Animes = append([]domain.Anime(nil), data.Animes...)
+	data.ContinueWatching = append(data.ContinueWatching[:0:0], data.ContinueWatching...)
+	if data.WatchlistMap != nil {
+		watchlistMap := make(map[int64]bool, len(data.WatchlistMap))
+		for id, ok := range data.WatchlistMap {
+			watchlistMap[id] = ok
+		}
+		data.WatchlistMap = watchlistMap
+	}
+	return data
 }