Issue with string.lower in lua code with cyrillic (LuaLaTeX)

Question

The string.lower function Lua does not work with Cyrillic. How to fix it?

MWE:

% !TeX program = lualatex
\documentclass[12pt]{article}
\usepackage{polyglossia}
\setdefaultlanguage[spelling=modern]{russian}
\setotherlanguage{english}
\defaultfontfeatures{Ligatures={TeX},Renderer=Basic}
\setmainfont{Times New Roman}

\def\ptestcyr{%
\directlua{
tex.print(string.lower("Supervisory Control And Data Acquisition"),"\string\\newline")
tex.print(string.lower("Ямало-Ненецкий Автономный Округ"))
}%
}
\begin{document}
\noindent\ptestcyr
\end{document}

Answer 1

As mentioned in the comments, you can write your own Tim Toady function.

Based on utf8data that you can download from https://github.com/artemshein/luv/blob/master/utf8data.lua and some code found in https://github.com/Stepets/utf8.lua/issues/13:

\documentclass[12pt]{article}
\usepackage{polyglossia}
\usepackage{luacode}
\setdefaultlanguage[spelling=modern]{russian}
\setotherlanguage{english}
\setmainfont{DejaVu Serif}
\begin{luacode}
require("utf8data")
function timtowtdilower(str_in)
  local lc_str = str_in:gsub(utf8.charpattern,utf8_uc_lc)
  return lc_str
end
\end{luacode}
\def\ptestcyr{%
\directlua{
tex.print(string.lower("Supervisory Control And Data Acquisition"),"\string\\newline")
tex.print(timtowtdilower("Ямало-Ненецкий Автономный Округ"))
}%
}
\begin{document}
\noindent\ptestcyr
\end{document}

Note that the font is different because I don't have Times New Roman installed.