Found my old LEL code and got the shell working, so tomorrow I'll try to make it layout some gui element.

tests/ansi_parser.cpp

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+#include <catch2/catch_test_macros.hpp>
+#include <fmt/core.h>
+#include <string>
+#include "ansi_parser.hpp"
+#include <codecvt>
+#include <iostream>
+
+#include "ftxui/dom/elements.hpp"  // for text, bgcolor, color, vbox, hbox, separator, operator|, Elements, Element, Fit, border
+#include "ftxui/dom/node.hpp"      // for Render
+#include "ftxui/screen/color.hpp"  // for Color, Color::Black, Color::Blue, Color::BlueLight, Color::Cyan, Color::CyanLight, Color::Default, Color::GrayDark, Color::GrayLight, Color::Green, Color::GreenLight, Color::Magenta, Color::MagentaLight, Color::Red, Color::RedLight, Color::White, Color::Yellow, Color::YellowLight, Color::Palette256, ftxui
+#include <ftxui/screen/color_info.hpp>  // for ColorInfo
+#include <ftxui/screen/screen.hpp>      // for Full, Screen
+#include <ftxui/screen/screen.hpp>      // for Full, Screen
+#include <ftxui/screen/terminal.hpp>  // for ColorSupport, Color, Palette16, Palette256, TrueColor
+#include "render.hpp"
+
+using namespace fmt;
+using namespace ftxui;
+
+std::string generate_colors() {
+  SFMLRender::init_terminal();
+
+  REQUIRE(ftxui::Terminal::ColorSupport() == ftxui::Terminal::Color::TrueColor);
+
+  const int max_value = 255;
+  const int value_increment = 8;
+  const int hue_increment = 6;
+  int saturation = max_value;
+  Elements array;
+  int count = 0;
+
+  for (int value = 0; value < max_value; value += 2 * value_increment) {
+    Elements line;
+    for (int hue = 0; hue < max_value; hue += hue_increment) {
+      line.push_back(
+          text("#")                                    //
+          | ftxui::color(Color::HSV(hue, saturation, value))  //
+          | ftxui::bgcolor(Color::HSV(hue, saturation, value + value_increment)));
+      count++;
+    }
+    array.push_back(hbox(std::move(line)));
+  }
+
+  auto true_color_display = vbox({
+      vbox(std::move(array)),
+  });
+
+  auto document = vbox({hbox({
+      true_color_display,
+  })});
+
+  auto screen = Screen::Create(Dimension::Full(), Dimension::Fit(document));
+  Render(screen, document);
+  return screen.ToString();
+}
+
+TEST_CASE("test out ragel parser", "[gui]") {
+  SFMLRender::init_terminal();
+  sf::Color default_fg(0,0,0);
+  sf::Color default_bg(100,100,100);
+
+  // this sets the Truecolor so need to do it first
+  ANSIParser ansi(default_fg, default_bg);
+  std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>> $converter;
+  std::string colors = generate_colors();
+  std::wstring colors_utf = $converter.from_bytes(colors);
+
+  bool good = ansi.parse(colors_utf,
+      [&](sf::Color color[[maybe_unused]], sf::Color bgcolor[[maybe_unused]]){
+      },
+      [&](wchar_t ch) {
+      bool correct_char = ch == '#' || ch == ' ' || ch == '\n' || ch == '\r';
+      REQUIRE(correct_char);
+  });
+
+  REQUIRE(good);
+}

tests/lel.cpp

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+#include "lel.hpp"
+#include <catch2/catch_test_macros.hpp>
+#include <fmt/core.h>
+#include <string>
+#include "ansi_parser.hpp"
+#include <codecvt>
+#include <iostream>
+
+
+
+TEST_CASE("test basic ops", "[lel]") {
+  LELParser parser;
+
+  bool good = parser.parse(
+     "[ label_1         | label3      ]"
+     "[ (300,300)*text1 | (150)people ]"
+     "[ <label2         | _           ]"
+     "[ message         | buttons     ]");
+
+  REQUIRE(good);
+}