gplib/include/gp/ring_list.hpp

#pragma once
#include "gp_config.hpp"

#include "gp/algorithm/modifiers.hpp"
#include "gp/algorithm/tmp_manip.hpp"

#include <stddef.h>

namespace gp {
	template<typename T, typename allocator, bool copy_allocator = false, bool may_contain_self = false>
	class ring_list{
	public:
		class explorer;
		class node {
			T* value;
			node* prev;
			node* next;
		public:
			node(T* p)
			: value{p}
			, prev{this}
			, next{this}
			{}

			friend class gp::ring_list<T, allocator, copy_allocator, may_contain_self>::explorer;
			friend class gp::ring_list<T, allocator, copy_allocator, may_contain_self>;
		};

		class explorer {
			node* pos;
		public:
			explorer(node* v) 
			: pos{v}
			{}

			bool operator==(const explorer& oth) const {
				return pos == oth.pos;
			}

			bool operator!=(const explorer& oth) const {
				return pos != oth.pos;
			}

			explorer operator++() {
				pos = pos->next;
				return pos;
			}

			explorer operator++(int) {
				auto tmp = pos;
				pos = pos->next;
				return tmp;
			}

			explorer operator--() {
				pos = pos->prev;
				return pos;
			}

			explorer operator--(int) {
				auto tmp = pos;
				pos = pos->prev;
				return tmp;
			}

			T& operator*() {
				return *(pos->value);
			}

			friend class ring_list;
		};

	private:
		node* any_node;
		size_t sz;
		typename gp::either<
			copy_allocator,
			allocator,
			gp::reference_wrapper<allocator>
		>::type alloc;

		void stitch_around(node* n) {
			n->prev->next = n->next;
			n->next->prev = n->prev;
		}

	public:
		ring_list()
		: any_node{nullptr}
		, sz{0}
		, alloc{}
		{}

		ring_list(node* initial, allocator& _alloc)
		: any_node{initial}
		, sz{1}
		, alloc{_alloc}
		{}

		ring_list(allocator& _alloc)
		: any_node{nullptr}
		, sz{0}
		, alloc{_alloc}
		{}

		template<typename V = T, typename ...Args>
		bool insert(Args&&... elem) {
			allocator& used_allocator = alloc;
			void* mem;
			[[unlikely]] if(
				nullptr == (mem = used_allocator.allocate(sizeof(V)))
			) return false;
			T* p = new(mem) V(elem...);
			node* to_insert = nullptr;
			[[unlikely]] if(
				nullptr == (to_insert = reinterpret_cast<node*>(used_allocator.allocate(sizeof(node))))
			) return false;
			to_insert = new(to_insert) node(p);
			[[unlikely]] if (any_node == nullptr) 
			{
				any_node = to_insert;
			} else {
				to_insert->prev = any_node->prev;
				to_insert->next = any_node;
				to_insert->prev->next = to_insert;
				any_node->prev = to_insert;
			}
			return true;
		}

		explorer explore() {
			return any_node;
		}

		void remove(explorer value) {
			auto v = value.pos;
			if(v == any_node) {
				if(v->next == v) {
					any_node = nullptr;
				} else {
					any_node = any_node->next;
					stitch_around(v);
				}
			} else {
				stitch_around(v);
			}
			allocator& used_allocator = alloc;
			v->value->~T();
			gp_config::assertion(used_allocator.deallocate(v->value), "Bad free of value");
			v->~node();
			gp_config::assertion(used_allocator.deallocate(v), "Bad free of node");
		}

		~ring_list()
		{
			// TODO: Find a less hackish way to resove this issue
			if  constexpr (!may_contain_self) {
				while(any_node) {
					remove(explore());
				}
			}
		}
	};
}