chore(attachments): refactor building image preview

(cherry picked from commit 02c1de55c4b21863bb7500811e04bc0de9177089)

pkg/models/task_attachment.go

@@ -17,14 +17,21 @@
 package models
 
 import (
+	"bytes"
+	"image"
+	"image/png"
 	"io"
+	"strconv"
 	"time"
 
 	"code.vikunja.io/api/pkg/events"
-
 	"code.vikunja.io/api/pkg/files"
+	"code.vikunja.io/api/pkg/log"
+	"code.vikunja.io/api/pkg/modules/keyvalue"
 	"code.vikunja.io/api/pkg/user"
 	"code.vikunja.io/api/pkg/web"
+
+	"github.com/disintegration/imaging"
 	"xorm.io/xorm"
 )
 
@@ -185,6 +192,110 @@ func (ta *TaskAttachment) ReadAll(s *xorm.Session, _ web.Auth, _ string, page in
 	return attachments, len(attachments), numberOfTotalItems, err
 }
 
+func cacheKeyForTaskAttachmentPreview(id int64, size PreviewSize) string {
+	return "task_attachment_preview_" + strconv.FormatInt(id, 10) + "_size_" + string(size)
+}
+
+func (ta *TaskAttachment) GetPreviewFromCache(previewSize PreviewSize) []byte {
+	cacheKey := cacheKeyForTaskAttachmentPreview(ta.ID, previewSize)
+
+	var cached []byte
+	exists, err := keyvalue.GetWithValue(cacheKey, &cached)
+
+	// If the preview is not cached, return nil
+	if err != nil || !exists || cached == nil {
+		return nil
+	}
+
+	return cached
+}
+
+type PreviewSize string
+
+const (
+	PreviewSizeUnknown PreviewSize = "unknown"
+	PreviewSmall       PreviewSize = "sm"
+	PreviewMedium      PreviewSize = "md"
+	PreviewLarge       PreviewSize = "lg"
+	PreviewExtraLarge  PreviewSize = "xl"
+)
+
+func (previewSize PreviewSize) GetSize() int {
+	switch previewSize {
+	case PreviewSmall:
+		return 100
+	case PreviewMedium:
+		return 200
+	case PreviewLarge:
+		return 400
+	case PreviewExtraLarge:
+		return 800
+	case PreviewSizeUnknown:
+		return 0
+	default:
+		return 200
+	}
+}
+
+func GetPreviewSizeFromString(size string) PreviewSize {
+	switch size {
+	case "sm":
+		return PreviewSmall
+	case "md":
+		return PreviewMedium
+	case "lg":
+		return PreviewLarge
+	case "xl":
+		return PreviewExtraLarge
+	}
+
+	return PreviewSizeUnknown
+}
+
+func resizeImage(img image.Image, width int) *image.NRGBA {
+	resizedImg := imaging.Resize(img, width, 0, imaging.Lanczos)
+	log.Debugf(
+		"Resized attachment image from %vx%v to %vx%v for a preview",
+		img.Bounds().Size().X,
+		img.Bounds().Size().Y,
+		resizedImg.Bounds().Size().X,
+		resizedImg.Bounds().Size().Y,
+	)
+
+	return resizedImg
+}
+
+func (ta *TaskAttachment) GenerateAndSavePreviewToCache(previewSize PreviewSize) []byte {
+	img, _, err := image.Decode(ta.File.File)
+	if err != nil {
+		return nil
+	}
+
+	// Scale down the image to a minimum size
+	resizedImg := resizeImage(img, previewSize.GetSize())
+
+	// Get the raw bytes of the resized image
+	buf := &bytes.Buffer{}
+	if err := png.Encode(buf, resizedImg); err != nil {
+		return nil
+	}
+	previewImage, err := io.ReadAll(buf)
+	if err != nil {
+		return nil
+	}
+
+	// Store the preview image in the cache
+	cacheKey := cacheKeyForTaskAttachmentPreview(ta.ID, previewSize)
+	err = keyvalue.Put(cacheKey, previewImage)
+	if err != nil {
+		return nil
+	}
+
+	log.Infof("Attachment image preview for task attachment %v of size %v created and cached", ta.ID, previewSize)
+
+	return previewImage
+}
+
 // Delete removes an attachment
 // @Summary Delete an attachment
 // @Description Delete an attachment.