refactor: use dependency injection in backend

backend/internal/utils/file_util.go

@@ -2,6 +2,7 @@ package utils
 
 import (
 	"io"
+	"mime/multipart"
 	"os"
 	"path/filepath"
 	"strings"
@@ -71,3 +72,24 @@ func copyFile(srcFilePath, destFilePath string) error {
 
 	return nil
 }
+
+func SaveFile(file *multipart.FileHeader, dst string) error {
+	src, err := file.Open()
+	if err != nil {
+		return err
+	}
+	defer src.Close()
+
+	if err = os.MkdirAll(filepath.Dir(dst), 0o750); err != nil {
+		return err
+	}
+
+	out, err := os.Create(dst)
+	if err != nil {
+		return err
+	}
+	defer out.Close()
+
+	_, err = io.Copy(out, src)
+	return err
+}