// =====================================================================================================================
//  fennec, a free and open source game engine
//  Copyright © 2025  Medusa Slockbower
//
//  This program 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.
//
//  This program 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 this program.  If not, see <https://www.gnu.org/licenses/>.
// =====================================================================================================================

///
/// \file list.h
/// \brief List of elements
///
///
/// \details
/// \author Medusa Slockbower
///
/// \copyright Copyright © 2025 Medusa Slockbower ([GPLv3](https://www.gnu.org/licenses/gpl-3.0.en.html))
///
///

#ifndef FENNEC_CONTAINERS_LIST_H
#define FENNEC_CONTAINERS_LIST_H

#include <fennec/containers/dynarray.h>
#include <fennec/containers/list.h>
#include <fennec/containers/optional.h>
#include <fennec/memory/allocator.h>

#include <fennec/math/common.h>

namespace fennec
{

///
///
/// \brief wrapper for lists of elements
/// \details
/// | Property  | Value        |
/// |-----------|--------------|
/// | stable    | \emoji anger |
/// | access    | \f$O(1)\f$   |
/// | insertion | \f$O(1)\f$   |
/// | deletion  | \f$O(1)\f$   |
/// | space     | \f$O(N)\f$   |
///
/// \tparam TypeT value type
template<class TypeT, class Alloc = allocator<TypeT>>
struct list {
public:
	using alloc_t = typename allocator_traits<Alloc>::template rebind<TypeT>;
	using value_t = TypeT;
	static constexpr size_t npos = -1;

	class iterator;
	class const_iterator;

private:
	struct node;

public:
	using elem_t = node;

	constexpr list()
		: _table(), _freed(), _root(npos), _last(npos), _size(0) {
	}

	constexpr ~list() = default;

	constexpr bool size()     const { return _size; }
	constexpr bool capacity() const { return _table.capacity(); }
	constexpr bool empty()    const { return _root == npos; }

	constexpr value_t& operator[](int i) {
		assertd(i >= 0 && size_t(i) < _size, "Index out of Bounds");
		size_t n = _walk(i);
		assertd(n != npos, "Index out of Bounds");
		return *_table[n].data;
	}

	constexpr const value_t& operator[](int i) const {
		assertd(i >= 0 && size_t(i) < _size, "Index out of Bounds");
		size_t n = _walk(i);
		assertd(n != npos, "Index out of Bounds");
		return *_table[n].data;
	}

	void insert(const iterator& it, const value_t& x) {
		if (size() == capacity()) {
			_expand();
		}

		size_t n = it._n;
		size_t p = _next_free();
		fennec::construct(&_table[p].data, x);
		if (n == npos) {
			if (empty()) {
				_root = p;
				_table[p].next = npos;
				_table[p].prev = npos;
			} else {
				_table[p].prev = n;
				_table[p].next = npos;
				_last = n;
			}
			return;
		}
		_table[p].next = n;
		_table[p].prev = _prev(n);
		_table[n].prev = p;
		++_size;
	}

	void insert(const iterator& it, value_t&& x) {
		if (size() == capacity()) {
			_expand();
		}

		size_t n = it._n;
		size_t p = _next_free();
		fennec::construct(&_table[p].data, fennec::forward<value_t>(x));
		if (n == npos) {
			if (empty()) {
				_root = p;
				_table[p].next = npos;
				_table[p].prev = npos;
			} else {
				_table[p].prev = n;
				_table[p].next = npos;
				_last = n;
			}
			return;
		}
		_table[p].next = n;
		_table[p].prev = _prev(n);
		_table[n].prev = p;
		++_size;
	}

	void insert(size_t i, const value_t& x) {
		assert(i <= size(), "Index out of Bounds");
		if (size() == capacity()) {
			_expand();
		}

		size_t n = _walk(min(i, size_t(size() - 1)));
		size_t p = _next_free();
		fennec::construct(&_table[p].data, x);
		if (n == npos) {
			if (empty()) {
				_root = p;
				_table[p].next = npos;
				_table[p].prev = npos;
			} else {
				_table[p].prev = n;
				_table[p].next = npos;
				_last = n;
			}
			return;
		}
		_table[p].next = n;
		_table[p].prev = _prev(n);
		_table[n].prev = p;
		++_size;
	}

	void insert(size_t i, value_t&& x) {
		assert(i <= size(), "Index out of Bounds");
		if (size() == capacity()) {
			_expand();
		}

		size_t n = _walk(min(i, size_t(size() - 1)));
		size_t p = _next_free();
		fennec::construct(&_table[p].data, fennec::forward<value_t>(x));
		if (n == npos) {
			if (empty()) {
				_root = p;
				_table[p].next = npos;
				_table[p].prev = npos;
			} else {
				_table[p].prev = n;
				_table[p].next = npos;
				_last = n;
			}
			return;
		}
		_table[p].next = n;
		_table[p].prev = _prev(n);
		_table[n].prev = p;
		++_size;
	}

	template<typename...ArgsT>
	void emplace(size_t i, ArgsT&&...args) {
		assert(i <= size(), "Index out of Bounds");
		if (size() == capacity()) {
			_expand();
		}

		size_t n = _walk(min(i, size_t(size() - 1)));
		size_t p = _next_free();
		fennec::construct(&_table[p].data, fennec::forward<ArgsT>(args)...);
		if (n == npos) {
			if (empty()) {
				_root = p;
				_table[p].next = npos;
				_table[p].prev = npos;
			} else {
				_table[p].prev = n;
				_table[p].next = npos;
				_last = n;
			}
			return;
		}
		_table[p].next = n;
		_table[p].prev = _prev(n);
		_table[n].prev = p;
		++_size;
	}

	void push_front(const value_t& x) {
		this->insert(0, x);
	}

	void push_front(value_t&& x) {
		this->insert(0, fennec::forward<value_t>(x));
	}

	template<typename...ArgsT>
	void emplace_front(ArgsT...args) {
		this->emplace(0, fennec::forward<ArgsT>(args)...);
	}

	void push_back(const value_t& x) {
		this->insert(_size, x);
	}

	void push_back(value_t&& x) {
		this->insert(_size, fennec::forward<value_t>(x));
	}

	template<typename...ArgsT>
	void emplace_back(ArgsT...args) {
		this->emplace(_size, fennec::forward<ArgsT>(args)...);
	}

	void erase(size_t i) {
		size_t j = _walk(i);
		if (j == npos) return;
		if (not _table[j].data) return;

		// Get the prev and next indices
		size_t p = _prev(j);
		size_t n = _next(j);

		// clear the node
		_table[j].data = nullopt;
		_table[j].prev = npos;
		_table[j].next = npos;

		// Fix prev and next nodes
		if (p != npos) _table[p].next = n;
		else _root = n;
		if (n != npos) _table[n].prev = p;
		else _last = p;

		// Mark node as freed
		_freed.push_back(j);
	}

	void pop_front() {
		erase(0);
	}

	void pop_back() {
		erase(_size - 1);
	}

	constexpr value_t& front() {
		return *_table[_root].data;
	}

	constexpr const value_t& front() const {
		return *_table[_root].data;
	}

	constexpr value_t& back() {
		return *_table[_last].data;
	}

	constexpr const value_t& back() const {
		return *_table[_last].data;
	}

// ITERATOR ============================================================================================================

	class iterator {
	public:
		~iterator() {
			_list = nullptr;
		}

		// prefix operator
		constexpr friend iterator& operator++(iterator& rhs) {
			if (rhs._list->_next(rhs._n) < rhs._list->capacity()) {
				return rhs;
			}
			rhs._n = npos;
			return rhs;
		}

		constexpr friend iterator operator++(iterator& lhs, int) {
			iterator prev = lhs;
			++lhs;
			return prev;
		}

		constexpr value_t& operator*() {
			return *(_list->_table[_n].data);
		}

		constexpr value_t* operator->() {
			return &*(_list->_table[_n].data);
		}

		constexpr bool operator==(const iterator& it) {
			return _list == it._list and _n == it._n;
		}

		constexpr bool operator!=(const iterator& it) {
			return _list != it._list or _n != it._n;
		}

	private:
		list*  _list;
		size_t _n;
		friend list;

		iterator(list* ls, size_t n)
			: _list(ls)
			, _n(n) {
		}
	};

	class const_iterator {
	public:
		~const_iterator() {
			_list = nullptr;
		}

		// prefix operator
		constexpr friend const_iterator& operator++(const_iterator& rhs) {
			if (rhs._list->_next(rhs._n) < rhs._list->capacity()) {
				return rhs;
			}
			rhs._n = npos;
			return rhs;
		}

		constexpr friend const_iterator operator++(const_iterator& lhs, int) {
			const_iterator prev = lhs;
			++lhs;
			return prev;
		}

		constexpr const value_t& operator*() {
			return *(_list->_table[_n].data);
		}

		constexpr const value_t* operator->() {
			return &*(_list->_table[_n].data);
		}

		constexpr bool operator==(const const_iterator& it) {
			return _list == it._list and _n == it._n;
		}

		constexpr bool operator!=(const const_iterator& it) {
			return _list != it._list or _n != it._n;
		}

	private:
		const list*  _list;
		size_t _n;
		friend list;

		const_iterator(const list* ls, size_t n)
			: _list(ls)
			, _n(n) {
		}
	};

	constexpr iterator begin() {
		return iterator(this, _root);
	}

	constexpr iterator end() {
		return iterator(this, npos);
	}

	constexpr const_iterator begin() const {
		return const_iterator(this, _root);
	}

	constexpr const_iterator end() const {
		return const_iterator(this, npos);
	}

private:
	allocation<elem_t, alloc_t> _table;
	dynarray<size_t> _freed;
	size_t _root, _last, _size;

	friend class iterator;

	constexpr void _expand() {
		_table.creallocate(fennec::max(_table.capacity(), size_t(1)) * 2);
	}

	struct node {
		optional<value_t> data;
		size_t prev, next;

		constexpr node()
			: data()
			, prev(npos)
			, next(npos) {
		}

		constexpr node(size_t p, size_t n)
			: data()
			, prev(p)
			, next(n) {
		}

		constexpr node(size_t p, size_t n, value_t&& val)
			: data(fennec::forward<value_t>(val))
			, prev(p)
			, next(n) {
		}

		constexpr ~node() = default;

		constexpr void clear() {
			data = nullopt;
			prev = npos;
			next = npos;
		}
	};

	size_t _next(size_t n) const {
		return _table[n].next;
	}

	size_t _prev(size_t n) const {
		return _table[n].prev;
	}

	size_t _walk(size_t i) const {
		size_t n = _root;
		if (n == npos) return n;
		while (i > 0 && n != npos) {
			n = _next(n); --i;
		}
		return n;
	}

	size_t _next_free() {
		if (not _freed.empty()) {
			size_t n = _freed.back();
			_freed.pop_back();
			return n;
		}
		_table[_size];
		return _size;
	}
};

}

#endif // FENNEC_CONTAINERS_LIST_H