open-cpp-utils/object_pool.h

// =====================================================================================================================
//  open-cpp-utils, an open-source cpp library with data structures that extend the STL.
//  Copyright (C) 2024  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/>.
// =====================================================================================================================

#ifndef OPEN_CPP_UTILS_OBJECT_POOL_H
#define OPEN_CPP_UTILS_OBJECT_POOL_H

#include <deque>

#include "allocation.h"
#include "optional.h"

namespace open_cpp_utils
{

/**
 * \brief
 * \tparam T
 */
template<typename T>
class object_list
{
// Typedefs ============================================================================================================

public:
    using value_type      = T;
    using pointer         = T*;
    using const_pointer   = const T*;
    using reference       = T&;
    using const_reference = const T&;

    using uuid_type  = uint64_t;

	class iterator;
	class const_iterator;

private:
    using node       = optional<value_type>;
	using obj_alloc  = std::vector<node>;
	using free_stack = std::deque<uuid_type>;


// Functions ===========================================================================================================

public:

// Constructors & Destructor -------------------------------------------------------------------------------------------

    object_list() = default;
    object_list(const object_list& other) = default;
    object_list(object_list&& other) = default;
    ~object_list() = default;


// Modifiers -----------------------------------------------------------------------------------------------------------

    size_t size() const { return data_.size(); }
	size_t capacity() const { return data_.capacity(); }


// Modifiers -----------------------------------------------------------------------------------------------------------

    void clear() { data_.clear(); freed_.clear(); }

    uuid_type insert(const_reference& value);
    void      erase(uuid_type id);

    object_list& operator=(const object_list&) = default;
    object_list& operator=(object_list&&) = default;


// Accessors -----------------------------------------------------------------------------------------------------------
	
    reference       operator[](uuid_type id)       { assert(data_[id]()); return data_[id]; }
    const_reference operator[](uuid_type id) const { assert(data_[id]()); return data_[id]; }
    bool            operator()(uuid_type id) const { return data_[id](); }

	iterator begin() { return { this, data_.begin() }; }
	iterator end()   { return { this, data_.end()   }; }

	const_iterator begin() const { return { this, data_.begin() }; }
	const_iterator end()   const { return { this, data_.end()   }; }

// Variables ===========================================================================================================

private:
    obj_alloc  data_;
    free_stack freed_;

public:
	class iterator
	{
	public:
		using obj_iterator = typename obj_alloc::iterator;
		
		iterator(object_list* list, obj_iterator start) : list_(list), it_(start)
		{
			while(it_ != list_->data_.end() && not (*it_)()) { ++it_; }
		}

		iterator& operator++()
		{
			++it_;
			while(it_ != list_->data_.end() && not (*it_)()) { ++it_; }
			return *this;
		}
		
		iterator  operator++(int)
		{
			iterator ret = this;
			++it_;
			while(it_ != list_->data_.end() && not (*it_)()) { ++it_; }
			return ret;
		}

		reference operator*() { return *it_; }

		bool operator==(const iterator& other) const { return list_ == other.list_ && it_ == other.it_; }
		bool operator!=(const const_iterator& other) const { return list_ != other.list_ || it_ != other.it_; }

		uuid_type id() { return (&*it_) - list_->data_.data(); } // Convert to node pointer
		
	private:
		object_list* list_;
		obj_iterator it_;
	};
	
	class const_iterator
	{
	public:
		using obj_iterator = typename obj_alloc::pointer;
		
		const_iterator(const object_list* list, obj_iterator start) : list_(list), it_(start) { }

		const_iterator& operator++()
		{ ++it_; while(it_ != list_->data_.end() && not (*it_)()) { ++it_; } return *this; }
		
		const_iterator  operator++(int)
		{ const_iterator ret = this; ++it_; while(it_ != list_->data_.end() && not (*it_)()) { ++it_; } return ret; }

		const_reference operator*() { return *it_; }

		bool operator==(const const_iterator& other) const { return list_ == other.list_ && it_ == other.it_; }
		bool operator!=(const const_iterator& other) const { return list_ != other.list_ || it_ != other.it_; }

		uuid_type id() { return (&*it_) - list_->data_.data(); } // Convert to node pointer
		
	private:
		const object_list* list_;
		obj_iterator it_;
	};
};

template<typename T>
typename object_list<T>::uuid_type object_list<T>::insert(const_reference value)
{
    if(freed_.empty()) { data_.push_back(value); return data_.size() - 1; }

    uuid_type id = freed_.back(); freed_.pop_back();
    data_[id] = value;
    return id;
}

template<typename T>
void object_list<T>::erase(uuid_type id)
{
    data_[id].reset();
    freed_.push_back(id);
}

} // open_cpp_utils

#endif // OPEN_CPP_UTILS_OBJECT_POOL_H