#ifndef XMLESCAPE_HH

#define XMLESCAPE_HH

#include <array>

#include <string>

#include <string_view>

// The following routines do the following substitutions:

//  & -> &   must always be done

//  < -> &lt;    must always be done

//  > -> >    always allowed, but must be done when it appears as ]]>

//  ' -> '  always allowed, but must be done inside quoted attribute

//  " -> "  always allowed, but must be done inside quoted attribute

//  all chars less than 32 -> &#xnn;

// So to simplify things we always do these 5+32 substitutions.

// This is a low-level version. It takes an input string and an output-functor.

// That functor is called (possibly) multiple times, each with a (small) chunk

// for the final output (chunk are either parts of the input or xml escape

// sequences).

template<typename Output>

inline void XMLEscape(std::string_view s, Output output)

{

	auto chunk = s.begin();

	auto last = s.end();

	auto it = chunk;

	while (it != last) {

		char c = *it;

		if (auto uc = static_cast<unsigned char>(c); uc < 32) {

			output(std::string_view(chunk, it));

			std::array<char, 6> buf = {'&', '#', 'x', '0', '0', ';'};

			auto hex = [](unsigned x) { return (x < 10) ? char(x + '0') : char(x - 10 + 'a'); };

			buf[3] = hex(uc / 16);

			buf[4] = hex(uc % 16);

			output(std::string_view(buf.data(), sizeof(buf)));

			chunk = ++it;

		} else if (c == '<') {

			output(std::string_view(chunk, it));

			output("<");

			chunk = ++it;

		} else if (c == '>') {

			output(std::string_view(chunk, it));

			output(">");

			chunk = ++it;

		} else if (c == '&') {

			output(std::string_view(chunk, it));

			output("&");

			chunk = ++it;

		} else if (c == '"') {

			output(std::string_view(chunk, it));

			output(""");

			chunk = ++it;

		} else if (c == '\'') {

			output(std::string_view(chunk, it));

			output("'");

			chunk = ++it;

		} else {

			// no output yet

			++it;

		}

	}

	output(std::string_view(chunk, last));

}

// Like above, but produces the output as a (single) std::string.

inline std::string XMLEscape(std::string_view s)

{

	std::string result;

	XMLEscape(s, [&](std::string_view chunk) { result += chunk; });

	return result;

}

#endif