/*
This file is part of Telegram Desktop,
the official desktop version of Telegram messaging app, see https://telegram.org

Telegram Desktop 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.

It 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.

In addition, as a special exception, the copyright holders give permission
to link the code of portions of this program with the OpenSSL library.

Full license: https://github.com/telegramdesktop/tdesktop/blob/master/LICENSE
Copyright (c) 2014-2017 John Preston, https://desktop.telegram.org
*/
#pragma once

#include <mapbox/variant.hpp>

// We use base::variant<> alias and base::get_if() helper while we don't have std::variant<>.
namespace base {

struct null_variant_type {
};

inline constexpr null_variant_type null_variant() {
	return null_variant_type {};
}

inline bool operator<(null_variant_type a, null_variant_type b) {
	return false;
}

inline bool operator==(null_variant_type a, null_variant_type b) {
	return true;
}

template <typename... Types>
using variant = mapbox::util::variant<Types...>;

template <typename T, typename... Types>
inline T *get_if(variant<Types...> *v) {
	return (v && v->template is<T>()) ? &v->template get_unchecked<T>() : nullptr;
}

template <typename T, typename... Types>
inline const T *get_if(const variant<Types...> *v) {
	return (v && v->template is<T>()) ? &v->template get_unchecked<T>() : nullptr;
}

template <typename... Types>
using optional_variant = variant<null_variant_type, Types...>;

template <typename... Types>
inline bool is_null_variant(const optional_variant<Types...> &variant) {
	return get_if<null_variant_type>(&variant) != nullptr;
}

template <typename Type>
using optional = optional_variant<Type>;

using null_optional_type = null_variant_type;

template <typename Type>
inline Type *get_if(optional<Type> *v) {
	return (v && v->template is<Type>()) ? &v->template get_unchecked<Type>() : nullptr;
}

template <typename Type>
inline const Type *get_if(const optional<Type> *v) {
	return (v && v->template is<Type>()) ? &v->template get_unchecked<Type>() : nullptr;
}

template <typename Type>
inline bool is_null_optional(const optional<Type> &optional) {
	return is_null_variant(optional);
}

inline constexpr null_optional_type null_optional() {
	return null_optional_type {};
}

} // namespace base