diff --git a/helpers.inc.php b/helpers.inc.php
index 97380e7..0ba8f6d 100644
--- a/helpers.inc.php
+++ b/helpers.inc.php
@@ -275,6 +275,30 @@ function gen_file(string $tpl_file, string $result_file, $deps = array(), $force
   }
 }
 
+function gen_to_dir(string $output_dir, array $rel_file2output)
+{
+  $existing_files = scan_files_rec([$output_dir]);
+
+  $gen_files = [];
+  foreach($rel_file2output as $output_file => $output_text)
+  {
+    $gen_file = $output_dir.'/'.$output_file;
+    $gen_files[] = $gen_file;
+    ensure_write($gen_file, $output_text);
+  }
+
+  $obsolete_files = array_diff(
+    array_map(function($file) { return normalize_path($file, true); }, $existing_files),
+    array_map(function($file) { return normalize_path($file, true); }, $gen_files)
+  );
+
+  foreach($obsolete_files as $file)
+    ensure_rm($file);
+
+  //this is really important to change directory last modified time
+  touch($output_dir);
+}
+
 function ensure_read($file)
 {
   $c = file_get_contents($file);