/*
 * rfc4251.h -- implements types from RFC 4251, section 5
 *
 * rfc4251::byte	byte
 * rfc4251::boolean	boolean
 * rfc4251::uint32	uint32
 * rfc4251::uint64	uint64
 * rfc4251::string	string
 * rfc4251::mpint	mpint
 * rfc4251::name_list	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());
		}
	};

	template<typename Length_Type>
	struct variable_length  : boost::totally_ordered<variable_length<Length_Type>> {
		using length_type = Length_Type;
		static_assert(std::is_unsigned_v<length_type>, "negative lengths are not supported");

		std::vector<char> buf;

		variable_length () = default;
		explicit variable_length (std::istream & is) { is >> *this; }

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

		friend std::istream & operator>> (std::istream & is, variable_length & v) {
			if (length_type const len{fixed_length<length_type>{is}}; is) {
				v.buf.clear();
				v.buf.resize(len);
				is.read(v.buf.data(), len);
			}
			return is;
		}
		friend std::ostream & operator<< (std::ostream & os, variable_length const & v) {
			check_length_against_limit(v.buf.size());
			if (os << fixed_length<length_type>{static_cast<length_type>(v.buf.size())})
				os.write(v.buf.data(), v.buf.size());
			return os;
		}
		friend bool operator== (variable_length const & l, variable_length const & r) {
			return l.buf == r.buf;
		}
		friend bool operator< (variable_length const & l, variable_length const & r) {
			return l.buf < r.buf;
		}

		constexpr static void check_length_against_limit(size_t const length) {
			if (length > std::numeric_limits<length_type>::max())
				throw std::length_error{"numeric limit for length field in rfc4251::variable_length type exceeded"};
		}

	};
}

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 : internal::variable_length<uint32_t> {
	using variable_length::variable_length;

	inline explicit string (char const * s, size_t l) {
		check_length_against_limit(l);
		buf.insert(buf.end(), s, s + l);
	}
	explicit string (std::string const & s) : string{s.data(), s.size()} {}

	operator std::string () const { return {buf.cbegin(), buf.cend()}; }
};

struct name_list : internal::variable_length<uint32_t> {
	using variable_length::variable_length;
	
	explicit name_list (std::vector<std::string> const &);
	
	operator std::vector<std::string> () const;
};

struct mpint : internal::variable_length<uint32_t> {
	using variable_length::variable_length;
	
	explicit mpint (mpz_srcptr);
	explicit mpint (mpz_class const & x) : mpint{x.get_mpz_t()} {}
	
	operator mpz_class () const;
};

}