#pragma once

#if !defined(MIJIN_UTIL_ANNOT_HPP_INCLUDED)
#define MIJIN_UTIL_ANNOT_HPP_INCLUDED 1

#include <utility>
#include "../internal/common.hpp"
#include "../debug/assert.hpp"

#if !defined(__has_include)
    #define __has_include(x) (false)
#endif

#if !defined(MIJIN_USE_GSL)
#if __has_include(<gsl/gsl>)
    #define MIJIN_USE_GSL 1
#else
    #define MIJIN_USE_GSL 0
#endif
#endif // !defined(MIJIN_USE_GSL)

#include <concepts>
#include "./concepts.hpp"

#if MIJIN_USE_GSL
    #include <gsl/gsl>
#endif

namespace mijin
{
template<typename T>
concept nullable_type = !std::is_same_v<T, std::nullptr_t> && requires(T t) { t == nullptr; };

template<nullable_type T>
class NotNullable
{
private:
    T base_;
public:
    template<typename U> requires(std::is_same_v<T, U> && std::is_copy_constructible_v<T>)
    constexpr NotNullable(U base) MIJIN_NOEXCEPT_IF(std::is_nothrow_copy_constructible_v<T>)
        : base_(base)
    {
        MIJIN_ASSERT(base_ != nullptr, "Constructed non-nullable type with nullptr.");
    }
    template<typename TOther> requires(std::is_constructible_v<T, const TOther&>)
    constexpr NotNullable(const NotNullable<TOther>& other) MIJIN_NOEXCEPT_IF((std::is_nothrow_constructible_v<T, const TOther&>))
            : base_(other.base_)
    {
        MIJIN_ASSERT(base_ != nullptr, "Constructed non-nullable type with nullptr.");
    }
    template<typename TOther> requires(std::is_constructible_v<T, TOther&&>)
    constexpr NotNullable(NotNullable<TOther>&& other) MIJIN_NOEXCEPT_IF((std::is_nothrow_constructible_v<T, TOther&&>))
            : base_(std::exchange(other.base_, nullptr))
    {
        MIJIN_ASSERT(base_ != nullptr, "Constructed non-nullable type with nullptr.");
    }
    template<typename TArg, typename... TArgs> requires(!std::is_same_v<TArg, std::nullptr_t>
                                                      && (!std::is_same_v<TArg, T> && sizeof...(TArgs) == 0)
                                                      && std::is_constructible_v<T, TArg&&, TArgs&&...>)
    constexpr NotNullable(TArg&& arg, TArgs&&... args) MIJIN_NOEXCEPT_IF((std::is_nothrow_constructible_v<T, TArg&&, TArgs&&...>))
        : base_(std::forward<TArg>(arg), std::forward<TArgs>(args)...)
    {
        MIJIN_ASSERT(base_ != nullptr, "Constructed non-nullable type with nullptr.");
    }
    constexpr NotNullable(T&& base) MIJIN_NOEXCEPT_IF(std::is_nothrow_move_constructible_v<T>)
                                    requires(std::is_move_constructible_v<T>)
        : base_(std::move(base))
    {
        MIJIN_ASSERT(base_ != nullptr, "Constructed non-nullable type with nullptr.");
    }
    constexpr NotNullable(NotNullable&& other) MIJIN_NOEXCEPT_IF(std::is_nothrow_move_constructible_v<T>)
                                               requires(std::is_move_constructible_v<T>)
        : base_(std::exchange(other.base_, nullptr))
    {
        MIJIN_ASSERT(base_ != nullptr, "Constructed non-nullable type with nullptr.");
    }
    constexpr NotNullable(std::nullptr_t) MIJIN_DELETE("Type is not nullable.");

    constexpr NotNullable& operator=(const NotNullable& other) MIJIN_NOEXCEPT_IF(std::is_nothrow_copy_constructible_v<T>)
                                                               requires(std::is_copy_constructible_v<T>)
    {
        if (this != &other)
        {
            this->base_ = other.base_;
        }
        MIJIN_ASSERT(base_ != nullptr, "Assigned nullptr to non-nullable type."); // might still happen if the other type was moved from
        return *this;
    }

    constexpr NotNullable& operator=(NotNullable&& other) MIJIN_NOEXCEPT_IF(std::is_nothrow_move_assignable_v<T>)
                                                          requires(std::is_move_assignable_v<T>)
    {
        if (this != &other)
        {
            this->base_ = std::exchange(other.base_, nullptr);
        }
        MIJIN_ASSERT(base_ != nullptr, "Assigned nullptr to non-nullable type."); // might still happen if the other type was moved from
        return *this;
    }

    constexpr NotNullable& operator=(std::nullptr_t) MIJIN_DELETE("Type is not nullable.");

    template<std::equality_comparable_with<T> TOther>
    bool operator==(const NotNullable<TOther>& other) MIJIN_NOEXCEPT_IF(noexcept(std::declval<T>() == std::declval<TOther>()))
    {
        return base_ == other.base_;
    }

    template<std::equality_comparable_with<T> TOther>
    bool operator!=(const NotNullable<TOther>& other) MIJIN_NOEXCEPT_IF(noexcept(std::declval<T>() != std::declval<TOther>()))
    {
        return base_ != other.base_;
    }

    template<std::equality_comparable_with<T> TOther> requires(!std::is_same_v<TOther, std::nullptr_t>)
    bool operator==(const TOther& other) MIJIN_NOEXCEPT_IF(noexcept(std::declval<T>() == std::declval<TOther>()))
    {
        return base_ == other;
    }

    template<std::equality_comparable_with<T> TOther> requires(!std::is_same_v<TOther, std::nullptr_t>)
    bool operator!=(const TOther& other) MIJIN_NOEXCEPT_IF(noexcept(std::declval<T>() != std::declval<TOther>()))
    {
        return base_ != other;
    }

    bool operator==(std::nullptr_t) MIJIN_DELETE("Type is not nullable.");
    bool operator!=(std::nullptr_t) MIJIN_DELETE("Type is not nullable.");

    constexpr operator const T&() const MIJIN_NOEXCEPT { return get(); }
    constexpr operator std::nullptr_t() const MIJIN_DELETE("Type is not nullable.");
    constexpr const T& operator->() const MIJIN_NOEXCEPT { return get(); }
    constexpr decltype(auto) operator*() const MIJIN_NOEXCEPT_IF(noexcept(*get())) { return *get(); }

    NotNullable& operator++() MIJIN_DELETE("Operator disabled for non-nullable types.");
    NotNullable& operator--() MIJIN_DELETE("Operator disabled for non-nullable types.");
    NotNullable operator++(int) MIJIN_DELETE("Operator disabled for non-nullable types.");
    NotNullable operator--(int) MIJIN_DELETE("Operator disabled for non-nullable types.");
    NotNullable& operator+=(std::ptrdiff_t) MIJIN_DELETE("Operator disabled for non-nullable types.");
    NotNullable& operator-=(std::ptrdiff_t) MIJIN_DELETE("Operator disabled for non-nullable types.");
    void operator[](std::ptrdiff_t) const MIJIN_DELETE("Operator disabled for non-nullable types.");

    [[nodiscard]]
    constexpr const T& get() const MIJIN_NOEXCEPT { return base_; }

    template<nullable_type TOther>
    friend class NotNullable;
};

#if MIJIN_USE_GSL
template<mijin::pointer_type T>
using owner_t = gsl::owner<T>;
#else
template<mijin::pointer_type T>
using owner_t = T;
#endif

template<typename T>
using not_null_t = NotNullable<T>;
}

#endif // !defined(MIJIN_UTIL_ANNOT_HPP_INCLUDED)