优化缩略图

internal/service/scraper_write_metadata_files_test.go

@@ -9,6 +9,7 @@ import (
 	"os"
 	"path/filepath"
 	"testing"
+	"time"
 
 	"github.com/glebarez/sqlite"
 	"go.uber.org/zap"
@@ -62,6 +63,47 @@ func TestWriteArtworkDataToPathReplacesExistingSidecar(t *testing.T) {
 	}
 }
 
+// TestWriteArtworkDataToPathSkipsUnchangedSidecar 验证"内容一致就不重写"：
+// 缩略图缓存键包含源文件的大小与 mtime，无谓的重写会让该条目所有尺寸的缩略图
+// 一起失效，下次浏览全部重新解码。
+func TestWriteArtworkDataToPathSkipsUnchangedSidecar(t *testing.T) {
+	scraper := &ScraperService{log: zap.NewNop()}
+	mediaDir := t.TempDir()
+	dst := scraper.writeArtworkDataToPath(mediaDir, "poster", "image/jpeg", testJPEG)
+	if dst == "" {
+		t.Fatal("expected a written destination path")
+	}
+	// 把 mtime 拨回过去，再写入完全相同的字节：文件必须原样保留。
+	past := time.Now().Add(-2 * time.Hour)
+	if err := os.Chtimes(dst, past, past); err != nil {
+		t.Fatal(err)
+	}
+	if got := scraper.writeArtworkDataToPath(mediaDir, "poster", "image/jpeg", testJPEG); got != dst {
+		t.Fatalf("destination = %q, want %q", got, dst)
+	}
+	info, err := os.Stat(dst)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if time.Since(info.ModTime()) < time.Minute {
+		t.Fatalf("mtime = %v, want the original past timestamp (identical artwork was rewritten)", info.ModTime())
+	}
+
+	// 内容变化时仍然必须覆盖。
+	changed := append([]byte(nil), testJPEG...)
+	changed[len(changed)-1] = 0x00
+	if got := scraper.writeArtworkDataToPath(mediaDir, "poster", "image/jpeg", changed); got != dst {
+		t.Fatalf("destination = %q, want %q", got, dst)
+	}
+	data, err := os.ReadFile(dst)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(data, changed) {
+		t.Fatal("changed artwork was not written")
+	}
+}
+
 func TestShouldCropAdultPosterWhenTMDbArtworkMatchedCodePath(t *testing.T) {
 	media := &model.Media{
 		Path:      filepath.Join(t.TempDir(), "IPX-235.mp4"),