2 files changed, 103 insertions, 0 deletions
diff --git a/internal/converter/processor_interface.go b/internal/converter/processor_interface.go
new file mode 100644
index 0000000..88b5ac3
--- /dev/null
+++ b/internal/converter/processor_interface.go
@@ -0,0 +1,8 @@
+package converter
+
+import "io"
+
+type Converter interface {
+	DeductOutputPath(inputPath string) string
+	Process(ext string, reader io.ReadCloser, writer io.WriteCloser) error
+}
diff --git a/internal/converter/webp.go b/internal/converter/webp.go
new file mode 100644
index 0000000..b7f1216
--- /dev/null
+++ b/internal/converter/webp.go
@@ -0,0 +1,95 @@
+package converter
+
+import (
+	"fmt"
+	"image"
+	"image/jpeg"
+	"image/png"
+	"io"
+	"log/slog"
+	"strings"
+
+	"golang.org/x/image/draw"
+
+	"github.com/SayaAndy/saya-today-thumbnail-generator/config"
+	"github.com/kolesa-team/go-webp/encoder"
+	"github.com/kolesa-team/go-webp/webp"
+)
+
+var _ Converter = (*WebpConverter)(nil)
+
+type WebpConverter struct {
+	maxWidth  int
+	maxHeight int
+	quality   int
+}
+
+func NewWebpConverter(cfg *config.ConverterConfig) (*WebpConverter, error) {
+	if cfg.Type != "webp" {
+		return nil, fmt.Errorf("invalid storage type for WebpConverter")
+	}
+	webpCfg := cfg.Config.(*config.WebpConfig)
+
+	return &WebpConverter{webpCfg.Size.MaxWidth, webpCfg.Size.MaxHeight, webpCfg.Quality}, nil
+}
+
+func (p *WebpConverter) DeductOutputPath(inputPath string) string {
+	pathParts := strings.Split(inputPath, ".")
+	if len(pathParts) < 2 {
+		return inputPath + ".webp"
+	}
+	pathParts[len(pathParts)-1] = "webp"
+	return strings.Join(pathParts, ".")
+}
+
+func (p *WebpConverter) Process(contentType string, reader io.ReadCloser, writer io.WriteCloser) error {
+	var src image.Image
+	var err error
+
+	defer reader.Close()
+	defer writer.Close()
+
+	switch contentType {
+	case "image/jpeg":
+		src, err = jpeg.Decode(reader)
+		if err != nil {
+			return fmt.Errorf("decode jpeg: %w", err)
+		}
+	case "image/png":
+		src, err = png.Decode(reader)
+		if err != nil {
+			return fmt.Errorf("decode png: %w", err)
+		}
+	default:
+		return fmt.Errorf("unsupported content type: %s", contentType)
+	}
+
+	opts, err := encoder.NewLossyEncoderOptions(encoder.PresetDefault, float32(p.quality))
+	if err != nil {
+		return fmt.Errorf("create webp encoder options: %w", err)
+	}
+
+	xCoef := float64(p.maxWidth) / float64(src.Bounds().Max.X)
+	if p.maxWidth == 0 {
+		xCoef = 1
+	}
+	yCoef := float64(p.maxHeight) / float64(src.Bounds().Max.Y)
+	if p.maxHeight == 0 {
+		yCoef = 1
+	}
+	slog.Debug("calculated coefficients", slog.Float64("x_coef", xCoef), slog.Float64("y_coef", yCoef))
+
+	if xCoef > 1 && yCoef > 1 {
+		return webp.Encode(writer, src, opts)
+	}
+
+	minCoef := xCoef
+	if yCoef < minCoef {
+		minCoef = yCoef
+	}
+
+	dst := image.NewRGBA(image.Rect(0, 0, int(float64(src.Bounds().Max.X)*minCoef+0.5), int(float64(src.Bounds().Max.Y)*minCoef+0.5)))
+	draw.CatmullRom.Scale(dst, dst.Rect, src, src.Bounds(), draw.Over, nil)
+
+	return webp.Encode(writer, dst, opts)
+}