1 files changed, 116 insertions, 0 deletions
diff --git a/internal/processor/image.go b/internal/processor/image.go
new file mode 100644
index 0000000..9a7d769
--- /dev/null
+++ b/internal/processor/image.go
@@ -0,0 +1,116 @@
+package processor
+
+import (
+	"fmt"
+	"image"
+	"image/gif"
+	"image/jpeg"
+	"image/png"
+	"os"
+	"path/filepath"
+
+	"golang.org/x/image/draw"
+)
+
+const (
+	maxImageWidth  = 1024
+	jpegQuality    = 80
+)
+
+// processImage reads the source image, resizes it if wider than maxImageWidth,
+// encodes it as JPEG at jpegQuality, and writes the result to destDir.
+// Returns the output filename (always a .jpg) and an HTML <img> snippet.
+func processImage(srcPath, destDir, postID string) (filename, htmlContent string, err error) {
+	img, err := decodeImage(srcPath)
+	if err != nil {
+		return "", "", err
+	}
+
+	img = resizeIfNeeded(img)
+
+	outName := "image.jpg"
+	outPath := filepath.Join(destDir, outName)
+
+	if err := writeJPEG(img, outPath); err != nil {
+		return "", "", err
+	}
+
+	// The <img> src is relative to the site root, pointing into the posts dir.
+	src := fmt.Sprintf("posts/%s/%s", postID, outName)
+	html := fmt.Sprintf(`<img src="%s" alt="" class="post-image">`, src)
+
+	return outName, html, nil
+}
+
+// decodeImage decodes a JPEG, PNG, or GIF (first frame) from srcPath.
+func decodeImage(srcPath string) (image.Image, error) {
+	f, err := os.Open(srcPath)
+	if err != nil {
+		return nil, fmt.Errorf("open image %s: %w", srcPath, err)
+	}
+	defer f.Close()
+
+	ext := filepath.Ext(srcPath)
+	switch ext {
+	case ".jpg", ".jpeg":
+		img, err := jpeg.Decode(f)
+		if err != nil {
+			return nil, fmt.Errorf("decode JPEG %s: %w", srcPath, err)
+		}
+		return img, nil
+
+	case ".png":
+		img, err := png.Decode(f)
+		if err != nil {
+			return nil, fmt.Errorf("decode PNG %s: %w", srcPath, err)
+		}
+		return img, nil
+
+	case ".gif":
+		// Use only the first frame of animated GIFs.
+		g, err := gif.Decode(f)
+		if err != nil {
+			return nil, fmt.Errorf("decode GIF %s: %w", srcPath, err)
+		}
+		return g, nil
+
+	default:
+		return nil, fmt.Errorf("unsupported image format: %s", ext)
+	}
+}
+
+// resizeIfNeeded returns a resized copy of img if its width exceeds maxImageWidth,
+// preserving aspect ratio. Otherwise the original is returned unchanged.
+func resizeIfNeeded(img image.Image) image.Image {
+	bounds := img.Bounds()
+	w := bounds.Dx()
+
+	if w <= maxImageWidth {
+		return img
+	}
+
+	h := bounds.Dy()
+	newW := maxImageWidth
+	newH := (h * newW) / w
+
+	dst := image.NewRGBA(image.Rect(0, 0, newW, newH))
+	draw.BiLinear.Scale(dst, dst.Bounds(), img, bounds, draw.Over, nil)
+
+	return dst
+}
+
+// writeJPEG encodes img as JPEG at the configured quality level and writes to path.
+func writeJPEG(img image.Image, path string) error {
+	f, err := os.Create(path)
+	if err != nil {
+		return fmt.Errorf("create JPEG %s: %w", path, err)
+	}
+	defer f.Close()
+
+	opts := &jpeg.Options{Quality: jpegQuality}
+	if err := jpeg.Encode(f, img, opts); err != nil {
+		return fmt.Errorf("encode JPEG %s: %w", path, err)
+	}
+
+	return nil
+}