docs: public static File getStorageDirectory(File parent_directory, String new_child_directory_name){
  
          File result = new File(parent_directory, new_child_directory_name);
          if(!result.exists())
              if(result.mkdir())
                  return result;
              else{
                  Log.e("getStorageDirectory", "Error creating " + result.getAbsolutePath());
                  return null;
              }
          else if(result.isFile()){
              return null;
          }
  
          Log.d("getStorageDirectory", "directory ready: " + result.getAbsolutePath());
          return result;
      }