Fennix/Kernel/include_std/iterator

/*
	This file is part of Fennix Kernel.

	Fennix Kernel 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.

	Fennix Kernel 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 Fennix Kernel. If not, see <https://www.gnu.org/licenses/>.
*/

#pragma once

#include <type_traits>
#include <cstddef>

namespace std
{
	struct input_iterator_tag
	{
	};

	struct output_iterator_tag
	{
	};

	struct forward_iterator_tag : public input_iterator_tag
	{
	};

	struct bidirectional_iterator_tag : public forward_iterator_tag
	{
	};

	struct random_access_iterator_tag : public bidirectional_iterator_tag
	{
	};

	struct contiguous_iterator_tag : public random_access_iterator_tag
	{
	};

	template <class Iter>
	struct iterator_traits
	{
	public:
		using difference_type = typename Iter::difference_type;
		using value_type = typename Iter::value_type;
		using pointer = typename Iter::pointer;
		using reference = typename Iter::reference;
		using iterator_category = typename Iter::iterator_category;
	};

	template <class T>
	struct iterator_traits<T *>
	{
	public:
		using difference_type = std::ptrdiff_t;
		using value_type = std::remove_cv_t<T>;
		using pointer = T *;
		using reference = T &;
		using iterator_category = std::random_access_iterator_tag;
		using iterator_concept = std::contiguous_iterator_tag;
	};

	namespace detail
	{
		template <class It>
		constexpr typename std::iterator_traits<It>::difference_type do_distance(It first, It last, std::input_iterator_tag)
		{
			typename std::iterator_traits<It>::difference_type result = 0;
			while (first != last)
			{
				++first;
				++result;
			}
			return result;
		}

		template <class It>
		constexpr typename std::iterator_traits<It>::difference_type do_distance(It first, It last, std::random_access_iterator_tag)
		{
			return last - first;
		}
	}

	template <class It>
	constexpr typename std::iterator_traits<It>::difference_type distance(It first, It last)
	{
		return detail::do_distance(first, last, typename std::iterator_traits<It>::iterator_category());
	}

	template <class InputIt>
	void __do_advance(InputIt &it, typename std::iterator_traits<InputIt>::difference_type n, std::input_iterator_tag)
	{
		while (n > 0)
		{
			--n;
			++it;
		}
	}

	template <class InputIt>
	void __do_advance(InputIt &it, typename std::iterator_traits<InputIt>::difference_type n, std::bidirectional_iterator_tag)
	{
		while (n > 0)
		{
			--n;
			++it;
		}
		while (n < 0)
		{
			++n;
			--it;
		}
	}

	template <class InputIt>
	void __do_advance(InputIt &it, typename std::iterator_traits<InputIt>::difference_type n, std::random_access_iterator_tag)
	{
		it += n;
	}

	template <class InputIt, class Distance>
	constexpr void advance(InputIt &it, Distance n)
	{
		__do_advance(it, typename std::iterator_traits<InputIt>::difference_type(n),
					 typename std::iterator_traits<InputIt>::iterator_category());
	}

	template <class BidirIt>
	constexpr BidirIt prev(BidirIt it, typename std::iterator_traits<BidirIt>::difference_type n = 1)
	{
		std::advance(it, -n);
		return it;
	}

	template <class InputIt>
	constexpr InputIt next(InputIt it, typename std::iterator_traits<InputIt>::difference_type n = 1)
	{
		std::advance(it, n);
		return it;
	}

	struct default_sentinel_t
	{
	};

	inline constexpr default_sentinel_t default_sentinel{};

	template <class T>
	using iter_value_t = typename std::iterator_traits<T>::value_type;

	template <class T>
	using iter_difference_t = typename std::iterator_traits<T>::difference_type;

	template <class T>
	using iter_reference_t = decltype(*std::declval<T &>());

	template <class Iter>
	class reverse_iterator
	{
	public:
		using iterator_type = Iter;
		using iterator_concept = std::bidirectional_iterator_tag;
		using iterator_category = std::iterator_traits<Iter>::iterator_category;
		using value_type = std::iter_value_t<Iter>;
		using difference_type = std::iter_difference_t<Iter>;
		using pointer = std::iterator_traits<Iter>::pointer;
		using reference = std::iter_reference_t<Iter>;

	protected:
		Iter current = Iter();

	public:
		reverse_iterator() = default;
		constexpr explicit reverse_iterator(Iter x) : current(x) {}
		// template <class U>
		// 	requires(!std::is_same_v<U, Iter> && std::convertible_to<const U &, Iter>)
		// constexpr explicit reverse_iterator(const U &other) : current(other.base())
		// {
		// }

		template <class U>
		reverse_iterator(const reverse_iterator<U> &other) : current(other.base()) {}

		template <class U>
		reverse_iterator &operator=(const reverse_iterator<U> &other)
		{
			current = other.base();
			return *this;
		}

		constexpr Iter base() const { return current; }

		constexpr decltype(auto) operator*() const
		{
			return *std::prev(current);
			// Iter tmp = current;
			// return *--tmp;
		}

		pointer operator->() const
		{
			if constexpr (std::is_pointer_v<Iter>)
				return current - 1;
			else
				return std::prev(current).operator->();
		}

		constexpr decltype(auto) operator[](difference_type n) const
		{
			return current[-n - 1];
		}

		constexpr reverse_iterator &operator++()
		{
			--current;
			return *this;
		}

		constexpr reverse_iterator operator++(int)
		{
			auto tmp = *this;
			--current;
			return tmp;
		}

		constexpr reverse_iterator &operator--()
		{
			++current;
			return *this;
		}

		constexpr reverse_iterator operator--(int)
		{
			auto tmp = *this;
			++current;
			return tmp;
		}

		constexpr reverse_iterator operator+(difference_type n) const
		{
			return reverse_iterator(current - n);
		}

		constexpr reverse_iterator operator-(difference_type n) const
		{
			return reverse_iterator(current + n);
		}

		constexpr reverse_iterator &operator+=(difference_type n)
		{
			current -= n;
			return *this;
		}

		constexpr reverse_iterator &operator-=(difference_type n)
		{
			current += n;
			return *this;
		}
	};
}