{ config, lib, pkgs, ... }:

with lib;
let
  isEmpty = lst: (length lst) == 0;
  isEmptyAttrs = attrs: (length (attrNames attrs)) == 0;
  renderAttr = name: value: ''${name}="${value}"'';
  renderAttrs = attrs:
    if (isEmptyAttrs attrs) then
      ""
    else
      " " + concatStringsSep " " (mapAttrsToList renderAttr attrs);
  renderTag = tag: attrs: body: "<${tag}${renderAttrs attrs}>${body}</${tag}>";
  # renderLoneTag = tag: attrs: "<${tag}${renderAttrs attrs} />";
  toXML = { tag, attrs ? { }, children ? [ ] }:
    let
      renderElement = el: if isString el then el else toXML el;
      body = concatStringsSep "" (map renderElement children);
    in renderTag tag attrs body;

  toXMLFile = name: content:
    let preformatXML = pkgs.writeText "${name}-preformat.xml" (toXML content);
    in pkgs.stdenv.mkDerivation {
      name = "${name}.xml";
      phases = [ "installPhase" ];
      buildInputs = with pkgs; [ xmlformat ];
      installPhase = "xmlformat ${preformatXML} > $out";
    };

  toFormattedXML = content:
    let xmlFile = toXMLFile "formatted-xml" content;
    in readFile xmlFile;
in { inherit toXML toXMLFile toFormattedXML; }