/*
 * rfc4251.h -- implements types from RFC 4251, section 5
 *
 * rfc4251::byte	byte
 * rfc4251::boolean	boolean
 * rfc4251::uint32	uint32
 * rfc4251::uint64	uint64
 * rfc4251::string	string, incl. mpint and name-list
 *
 * those structs contain the objects in their RFC 4251 representation,
 * conversions are provided via constructors and cast operators
 *
 * Copyright (C) 2013-2015,2021 Timo Weingärtner <timo@tiwe.de>
 *
 * This file is part of ssh-agent-filter.
 *
 * ssh-agent-filter is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * ssh-agent-filter is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with ssh-agent-filter.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <type_traits>
#include <cstdint>
#include <array>
#include <vector>
#include <string>
#include <iostream>
#include <limits>
#include <stdexcept>
#include <gmpxx.h>
#include <boost/operators.hpp>

namespace rfc4251 {

namespace internal {
	template<typename T>
	constexpr inline auto host_to_network (T value) noexcept {
		static_assert(std::is_unsigned_v<T>, "shift is only supported on unsigned");

		std::array<char, sizeof(T)> ret;
		for (auto it{rbegin(ret)}; it != rend(ret); ++it) {
			*it = value & 0xff;
			if constexpr (sizeof(T) > 1) value >>= 8;
		}
		return ret;
	}

	template<typename T>
	constexpr inline auto network_to_host (std::array<char, sizeof(T)> const buf) noexcept {
		static_assert(std::is_unsigned_v<T>, "shift is only supported on unsigned");

		T ret{0};
		for (auto it{cbegin(buf)}; it != cend(buf); ++it) {
			if constexpr (sizeof(T) > 1) ret <<= 8;
			ret |= static_cast<uint8_t>(*it);
		}
		return ret;
	}

	template<typename T>
	struct fixed_length {
		static_assert(std::is_unsigned_v<T>, "support for signed types might need more work");

		std::array<char, sizeof(T)> buf{};

		constexpr fixed_length () noexcept = default;
		constexpr explicit fixed_length (T const v) noexcept : buf{host_to_network(v)} {}
		explicit fixed_length (std::istream & is) { is >> *this; }

		constexpr operator T () const noexcept { return network_to_host<T>(buf); }

		friend std::istream & operator>> (std::istream & is, fixed_length & x) {
			return is.read(x.buf.data(), x.buf.size());
		}
		friend std::ostream & operator<< (std::ostream & os, fixed_length const & x) {
			return os.write(x.buf.data(), x.buf.size());
		}
	};
}

using byte    = internal::fixed_length<uint8_t>;
using boolean = internal::fixed_length<bool>;
using uint32  = internal::fixed_length<uint32_t>;
using uint64  = internal::fixed_length<uint64_t>;

struct string : boost::totally_ordered<string> {
	std::vector<char> value;
	
	string () = default;
	inline explicit string (char const *, size_t);
	explicit string (std::string const & s) : string{s.data(), s.size()} {}
	explicit string (std::vector<std::string> const &);
	explicit string (mpz_srcptr);
	explicit string (mpz_class const & x) : string{x.get_mpz_t()} {}
	inline explicit string (std::istream &);

	size_t size () const noexcept { return value.size(); }
	char const * data () const noexcept { return value.data(); }
	char * data () noexcept { return value.data(); }

	operator std::string () const { return {value.begin(), value.end()}; }
	operator std::vector<std::string> () const;
	operator mpz_class () const;
};

inline string::string (char const * s, size_t l) {
	if (l > std::numeric_limits<uint32_t>::max())
		throw std::length_error{"32-bit limit for rfc4251::string exceeded"};
	value.insert(value.end(), s, s + l);
}

inline std::istream & operator>> (std::istream & is, string & s) {
	s.value.clear();
	if (uint32_t const len{uint32{is}}; is) {
		s.value.resize(len);
		is.read(s.value.data(), len);
	}
	return is;
}

inline std::ostream & operator<< (std::ostream & os, string const & s) {
	if (s.value.size() > std::numeric_limits<uint32_t>::max())
		throw std::length_error{"32-bit limit for rfc4251::string exceeded"};
	if (os << uint32{static_cast<uint32_t>(s.value.size())})
		os.write(s.value.data(), s.value.size());
	return os;
}

inline string::string (std::istream & is) {
	is >> *this;
}

inline bool operator== (string const & l, string const & r) {
	return l.value == r.value;
}

inline bool operator< (string const & l, string const & r) {
	return l.value < r.value;
}

}