Add gated cover byte fetcher

backend/internal/latest/poller.go

@@ -16,8 +16,8 @@ type Fetcher interface {
 	Get(ctx context.Context, url string) (body string, status int, err error)
 }
 
-// CoverFetcher retrieves one kagane cover through the browser-backed path.
-type CoverFetcher interface {
+// BrowserCoverFetcher retrieves one kagane cover through the browser-backed path.
+type BrowserCoverFetcher interface {
 	Image(ctx context.Context, imageID string) (body []byte, contentType string, err error)
 }
 
@@ -42,9 +42,11 @@ type Poller struct {
 	// cannot clear. Nil disables those sites entirely rather than falling back
 	// to Fetch, which would only ever retrieve a challenge page.
 	BrowserFetch Fetcher
-	// CoverFetch is optional: it prefetches kagane covers without changing the
-	// chapter poll's result when the browser or persistence fails.
-	CoverFetch      CoverFetcher
+	// CoverFetch is optional; failures are logged and never affect the chapter poll.
+	CoverFetch BrowserCoverFetcher
+	// CoverBytesFetch is optional; it handles non-kagane sources through the same
+	// failure-isolated prefetch path.
+	CoverBytesFetch CoverBytesFetcher
 	Now             func() time.Time // injected so tests can freeze it
 	Cooldown        time.Duration
 	BrowserCooldown time.Duration
@@ -56,14 +58,39 @@ type Poller struct {
 var browserBackedSites = []string{"kagane", "novelfull"}
 
 func (p *Poller) prefetchCover(ctx context.Context, sr store.Series) {
-	if sr.Site != "kagane" || p.CoverFetch == nil {
+	if sr.Cover == "" {
 		return
 	}
-	imageID, ok := store.KaganeImageID(sr.Cover)
-	if !ok {
+	if sr.Site == "kagane" {
+		if p.CoverFetch == nil {
+			return
+		}
+		imageID, ok := store.KaganeImageID(sr.Cover)
+		if !ok {
+			return
+		}
+		_, _, found, err := p.Store.GetKaganeCover(imageID)
+		if err != nil {
+			log.Printf("latest poll %q: read cover: %v", sr.Key(), err)
+			return
+		}
+		if found {
+			return
+		}
+		body, contentType, err := p.CoverFetch.Image(ctx, imageID)
+		if err != nil {
+			log.Printf("latest poll %q: fetch cover: %v", sr.Key(), err)
+			return
+		}
+		if err := p.Store.PutKaganeCover(imageID, body, contentType); err != nil {
+			log.Printf("latest poll %q: persist cover: %v", sr.Key(), err)
+		}
 		return
 	}
-	_, _, found, err := p.Store.GetKaganeCover(imageID)
+	if p.CoverBytesFetch == nil {
+		return
+	}
+	_, _, found, err := p.Store.GetCover(sr.Cover)
 	if err != nil {
 		log.Printf("latest poll %q: read cover: %v", sr.Key(), err)
 		return
@@ -71,12 +98,12 @@ func (p *Poller) prefetchCover(ctx context.Context, sr store.Series) {
 	if found {
 		return
 	}
-	body, contentType, err := p.CoverFetch.Image(ctx, imageID)
+	body, contentType, err := p.CoverBytesFetch.Fetch(ctx, sr.Cover)
 	if err != nil {
 		log.Printf("latest poll %q: fetch cover: %v", sr.Key(), err)
 		return
 	}
-	if err := p.Store.PutKaganeCover(imageID, body, contentType); err != nil {
+	if err := p.Store.PutCover(sr.Cover, body, contentType); err != nil {
 		log.Printf("latest poll %q: persist cover: %v", sr.Key(), err)
 	}
 }