add image conversion for telegram

internal/media/convert.go

@@ -0,0 +1,66 @@
+package media
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"os/exec"
+	"strings"
+)
+
+const maxTelegramPhotoSize = 10 * 1024 * 1024 // 10 MB
+
+// CompressImage compresses an image if it exceeds Telegram's 10 MB photo limit.
+// It uses ImageMagick's magick command to convert via stdin/stdout.
+// Returns the (possibly compressed) data, updated filename, and any error.
+func CompressImage(ctx context.Context, data []byte, filename string) (out []byte, outName string, err error) {
+	if len(data) <= maxTelegramPhotoSize {
+		return data, filename, nil
+	}
+
+	// First attempt: just re-encode as JPEG with quality 85
+	out, err = runMagick(ctx, data, "-quality", "85")
+	if err != nil {
+		return nil, "", fmt.Errorf("compress image: %w", err)
+	}
+
+	newFilename := replaceExt(filename, ".jpg")
+
+	if len(out) <= maxTelegramPhotoSize {
+		return out, newFilename, nil
+	}
+
+	// Second attempt: resize to 50% and quality 85
+	out, err = runMagick(ctx, data, "-resize", "50%", "-quality", "85")
+	if err != nil {
+		return nil, "", fmt.Errorf("compress image with resize: %w", err)
+	}
+
+	if len(out) > maxTelegramPhotoSize {
+		return nil, "", fmt.Errorf("image still too large after compression (%d bytes)", len(out))
+	}
+
+	return out, newFilename, nil
+}
+
+func runMagick(ctx context.Context, data []byte, args ...string) ([]byte, error) {
+	cmdArgs := append([]string{"-"}, args...)
+	cmdArgs = append(cmdArgs, "jpeg:-")
+
+	cmd := exec.CommandContext(ctx, "magick", cmdArgs...)
+	cmd.Stdin = bytes.NewReader(data)
+
+	out, err := cmd.Output()
+	if err != nil {
+		return nil, fmt.Errorf("magick: %w", err)
+	}
+
+	return out, nil
+}
+
+func replaceExt(filename, newExt string) string {
+	if i := strings.LastIndex(filename, "."); i >= 0 {
+		return filename[:i] + newExt
+	}
+	return filename + newExt
+}