Add option to generate image thumbnails during generate (#4602)

* Add option to generate image thumbnails
* Limit number of concurrent image thumbnail generation ops

internal/manager/task_generate_image_thumbnail.go

@@ -0,0 +1,79 @@
+package manager
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"github.com/stashapp/stash/pkg/fsutil"
+	"github.com/stashapp/stash/pkg/image"
+	"github.com/stashapp/stash/pkg/logger"
+	"github.com/stashapp/stash/pkg/models"
+)
+
+type GenerateImageThumbnailTask struct {
+	Image     models.Image
+	Overwrite bool
+}
+
+func (t *GenerateImageThumbnailTask) GetDescription() string {
+	return fmt.Sprintf("Generating Thumbnail for image %s", t.Image.Path)
+}
+
+func (t *GenerateImageThumbnailTask) Start(ctx context.Context) {
+	if !t.required() {
+		return
+	}
+
+	thumbPath := GetInstance().Paths.Generated.GetThumbnailPath(t.Image.Checksum, models.DefaultGthumbWidth)
+	f := t.Image.Files.Primary()
+	path := f.Base().Path
+
+	logger.Debugf("Generating thumbnail for %s", path)
+
+	mgr := GetInstance()
+	c := mgr.Config
+
+	clipPreviewOptions := image.ClipPreviewOptions{
+		InputArgs:  c.GetTranscodeInputArgs(),
+		OutputArgs: c.GetTranscodeOutputArgs(),
+		Preset:     c.GetPreviewPreset().String(),
+	}
+
+	encoder := image.NewThumbnailEncoder(mgr.FFMpeg, mgr.FFProbe, clipPreviewOptions)
+	data, err := encoder.GetThumbnail(f, models.DefaultGthumbWidth)
+
+	if err != nil {
+		// don't log for animated images
+		if !errors.Is(err, image.ErrNotSupportedForThumbnail) {
+			logger.Errorf("[generator] getting thumbnail for image %s: %w", path, err)
+		}
+		return
+	}
+
+	err = fsutil.WriteFile(thumbPath, data)
+	if err != nil {
+		logger.Errorf("[generator] writing thumbnail for image %s: %w", path, err)
+		return
+	}
+}
+
+func (t *GenerateImageThumbnailTask) required() bool {
+	vf, ok := t.Image.Files.Primary().(models.VisualFile)
+	if !ok {
+		return false
+	}
+
+	if vf.GetHeight() <= models.DefaultGthumbWidth && vf.GetWidth() <= models.DefaultGthumbWidth {
+		return false
+	}
+
+	if t.Overwrite {
+		return true
+	}
+
+	thumbPath := GetInstance().Paths.Generated.GetThumbnailPath(t.Image.Checksum, models.DefaultGthumbWidth)
+	exists, _ := fsutil.FileExists(thumbPath)
+
+	return !exists
+}