优化首页分页和图片上传

backend/internal/modules/file/image_variants.go

@@ -0,0 +1,132 @@
+package file
+
+import (
+	"bytes"
+	"image"
+	"image/color"
+	"image/draw"
+	"image/jpeg"
+	_ "image/png"
+	"math"
+	"path"
+	"strings"
+
+	xdraw "golang.org/x/image/draw"
+	_ "golang.org/x/image/webp"
+)
+
+const (
+	ImageVariantThumb  = "thumb"
+	ImageVariantMedium = "medium"
+)
+
+const (
+	thumbMaxSide  = 480
+	mediumMaxSide = 1280
+)
+
+type generatedImageVariant struct {
+	Key         string
+	Content     []byte
+	ContentType string
+}
+
+type imageVariantConfig struct {
+	Name    string
+	MaxSide int
+	Quality int
+}
+
+var imageVariantConfigs = []imageVariantConfig{
+	{Name: ImageVariantThumb, MaxSide: thumbMaxSide, Quality: 76},
+	{Name: ImageVariantMedium, MaxSide: mediumMaxSide, Quality: 82},
+}
+
+func ImageVariantKey(key string, variant string) string {
+	ext := path.Ext(key)
+	base := strings.TrimSuffix(key, ext)
+	if base == "" {
+		base = key
+	}
+	return base + "." + variant + ".jpg"
+}
+
+func ImageVariantFallbackKeys(key string, variant string) []string {
+	if key == "" {
+		return nil
+	}
+	keys := []string{ImageVariantKey(key, variant)}
+	if strings.HasSuffix(key, ".medium.jpg") && variant == ImageVariantThumb {
+		keys = append(keys, strings.TrimSuffix(key, ".medium.jpg")+"."+ImageVariantThumb+".jpg")
+	}
+	keys = append(keys, key)
+	return dedupeKeys(keys)
+}
+
+func generateImageVariants(key string, data []byte, contentType string) []generatedImageVariant {
+	if !strings.HasPrefix(contentType, "image/") || contentType == "image/svg+xml" {
+		return nil
+	}
+	source, _, err := image.Decode(bytes.NewReader(data))
+	if err != nil {
+		return nil
+	}
+	var variants []generatedImageVariant
+	for _, config := range imageVariantConfigs {
+		rendered := resizeForVariant(source, config.MaxSide)
+		encoded, err := encodeJPEG(rendered, config.Quality)
+		if err != nil {
+			continue
+		}
+		variants = append(variants, generatedImageVariant{
+			Key:         ImageVariantKey(key, config.Name),
+			Content:     encoded,
+			ContentType: "image/jpeg",
+		})
+	}
+	return variants
+}
+
+func resizeForVariant(source image.Image, maxSide int) image.Image {
+	bounds := source.Bounds()
+	width := bounds.Dx()
+	height := bounds.Dy()
+	if width <= 0 || height <= 0 || maxSide <= 0 {
+		return source
+	}
+	scale := math.Min(float64(maxSide)/float64(width), float64(maxSide)/float64(height))
+	if scale > 1 {
+		scale = 1
+	}
+	targetWidth := max(1, int(math.Round(float64(width)*scale)))
+	targetHeight := max(1, int(math.Round(float64(height)*scale)))
+	target := image.NewRGBA(image.Rect(0, 0, targetWidth, targetHeight))
+	draw.Draw(target, target.Bounds(), &image.Uniform{C: color.White}, image.Point{}, draw.Src)
+	xdraw.ApproxBiLinear.Scale(target, target.Bounds(), source, bounds, draw.Over, nil)
+	return target
+}
+
+func encodeJPEG(source image.Image, quality int) ([]byte, error) {
+	var buffer bytes.Buffer
+	err := jpeg.Encode(&buffer, source, &jpeg.Options{Quality: quality})
+	if err != nil {
+		return nil, err
+	}
+	return buffer.Bytes(), nil
+}
+
+func dedupeKeys(keys []string) []string {
+	seen := make(map[string]struct{}, len(keys))
+	result := make([]string, 0, len(keys))
+	for _, key := range keys {
+		if key == "" {
+			continue
+		}
+		if _, ok := seen[key]; ok {
+			continue
+		}
+		seen[key] = struct{}{}
+		result = append(result, key)
+	}
+	return result
+}