//	Distributed under the Boost Software License Version 1.0 https://www.boost.org/LICENSE_1_0.txt
//	Copyright Gero Peterhoff

#ifndef INCLUDE_BOOST_ALGORITHM_STRING_CONCAT_HPP
#define INCLUDE_BOOST_ALGORITHM_STRING_CONCAT_HPP

#include <boost/utility/string_view.hpp>
#include <boost/config/config_more.hpp>
#include <boost/config.hpp>
#include <boost/mp11.hpp>
#include <algorithm>
#include <tuple>

#if !defined(BOOST_NO_CXX17_HDR_STRING_VIEW)
#include <string_view>
#endif



namespace boost
{
namespace algorithm
{
namespace detail
{
template <typename Char, typename Traits, typename Allocator>
BOOST_FORCEINLINE constexpr boost::basic_string_view<Char>	make_view(const std::basic_string<Char, Traits, Allocator>& str)	noexcept
{
	using view_type	= boost::basic_string_view<Char>;

	return view_type(str);
}

template <typename Char, typename Traits>
BOOST_FORCEINLINE constexpr boost::basic_string_view<Char>	make_view(const boost::basic_string_view<Char, Traits>& str)	noexcept
{
	return str;
}

#if !defined(BOOST_NO_CXX17_HDR_STRING_VIEW)
template <typename Char, typename Traits>
BOOST_FORCEINLINE constexpr boost::basic_string_view<Char>	make_view(const std::basic_string_view<Char, Traits>& str)	noexcept
{
	using view_type	= boost::basic_string_view<Char>;

	return view_type(str.data(), str.size());
}
#endif

template <typename Char>
BOOST_FORCEINLINE constexpr boost::basic_string_view<Char>	make_view(const Char* const str)	noexcept
{
	using view_type	= boost::basic_string_view<Char>;

	return view_type(str);
}

template <typename... Strings>
BOOST_FORCEINLINE constexpr auto	make_view_tuple(const Strings&... strs)	noexcept -> decltype(std::make_tuple(make_view(strs)...))
{
	return std::make_tuple(make_view(strs)...);
}

struct accumulate_view_size
{
	size_t
		size = 0;

	template <typename View>
	BOOST_FORCEINLINE BOOST_CXX20_CONSTEXPR void	operator()(const View& v)	noexcept
	{
		size += v.size();
	}
};

template <typename String>
struct concat_view
{
	String&
		value;
	typename String::iterator
		position;

	concat_view() = delete;
	BOOST_FORCEINLINE BOOST_CXX20_CONSTEXPR concat_view(String& res, const size_t view_size) noexcept : value{res}
	{
		using difference_type = typename String::difference_type;

		const size_t
			size = value.size();

		value.resize(view_size + size);
		position = std::next(value.begin(), difference_type(size));
	}

	template <typename View>
	BOOST_FORCEINLINE BOOST_CXX20_CONSTEXPR void	operator()(const View& v)	noexcept
	{
		position = std::copy(v.begin(), v.end(), position);
	}
};

}	//	detail



template <typename String, typename... Strings>
inline BOOST_CXX20_CONSTEXPR void	concat(String& res, const Strings&... strs)	noexcept
{
	const auto
		tup = detail::make_view_tuple(strs...);
	detail::accumulate_view_size
		acc;

	boost::mp11::tuple_for_each(tup, acc);

	detail::concat_view<String>
		ccv(res, acc.size);

	boost::mp11::tuple_for_each(tup, ccv);
}

template <typename String, typename... Strings>
inline BOOST_CXX20_CONSTEXPR String	concat_copy(const Strings&... strs)	noexcept
{
	String
		res;

	concat(res, strs...);
	return res;
}

}	//	algorithm
}	//	boost

#endif	//	INCLUDE_BOOST_ALGORITHM_STRING_CONCAT_HPP