#include <codecvt>
#include <cstdlib>
#include <cstring>
#include <cwctype>
#include <iostream>
#include <locale>
#include <vector>

using std::cout;
using std::endl;
using std::exit;
using std::memcmp;
using std::size_t;

using std::wcout;

int main(void)
{
  constexpr char16_t msg_utf16[] = u"¡Hola, mundo! \U0001F600"; // Shouldn't assume endianness.
  constexpr wchar_t msg_w[] = L"¡Hola, mundo! \U0001F600";
  constexpr char32_t msg_utf32[] = U"¡Hola, mundo! \U0001F600";
  constexpr char msg_utf8[] = u8"¡Hola, mundo! \U0001F600";

  // May vary from OS to OS>  "" is the most standard, but might require, e.g. "en_US.utf8".
  constexpr char locale_name[] = "";
  std::locale::global(std::locale(locale_name)); //
  wcout.imbue(std::locale());

  const std::codecvt_utf16<wchar_t, 0x1FFFF, std::little_endian> converter_w;
  const size_t max_len = sizeof(msg_utf16);
  std::vector<char> out(max_len);
  std::mbstate_t state;
  const wchar_t* from_w = nullptr;
  char* to_next = nullptr;

  converter_w.out( state, msg_w, msg_w+sizeof(msg_w)/sizeof(wchar_t), from_w, out.data(), out.data() + out.size(), to_next );

  
  if (memcmp( msg_utf8, out.data(), sizeof(msg_utf8) ) == 0 ) {
    wcout << L"std::codecvt_utf16<wchar_t> converts to UTF-8, not UTF-16!" << endl;
  } else if ( memcmp( msg_utf16, out.data(), max_len ) != 0 ) {
    wcout << L"std::codecvt_utf16<wchar_t> conversion not equal!" << endl;
  } else {
    wcout << L"std::codecvt_utf16<wchar_t> conversion is correct." << endl;
  }
  out.clear();
  out.resize(max_len);

  const std::codecvt_utf16<char32_t, 0x1FFFF, std::little_endian> converter_u32;
  const char32_t* from_u32 = nullptr;
  converter_u32.out( state, msg_utf32, msg_utf32+sizeof(msg_utf32)/sizeof(char32_t), from_u32, out.data(), out.data() + out.size(), to_next );

  if ( memcmp( msg_utf16, out.data(), max_len ) != 0 ) {
    wcout << L"std::codecvt_utf16<char32_t> conversion not equal!" << endl;
  } else {
    wcout << L"std::codecvt_utf16<char32_t> conversion is correct." << endl;
  }

  wcout << msg_w << endl;
  return EXIT_SUCCESS;
}