sparse_map.hpp

/* clang-format off */
 
/*
  stellarlib
  Copyright (C) 2025-2026 Domán Zana
 
  This software is provided 'as-is', without any express or implied
  warranty. In no event will the authors be held liable for any damages
  arising from the use of this software.
 
  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:
 
  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.
*/
 
#ifndef STELLARLIB_ECS_SPARSE_MAP_HPP
#define STELLARLIB_ECS_SPARSE_MAP_HPP
 
#include <stellarlib/ecs/any_set.hpp>
#include <stellarlib/ecs/stack_vector.hpp>
 
#include <limits>
#include <memory>
#include <ranges>
#include <type_traits>
#include <utility>
 
namespace stellarlib::ecs::internal
{
template <typename Key, typename T>
class sparse_map final : public any_set<Key>
{
public:
    [[nodiscard]]
    constexpr sparse_map() noexcept = default;
 
    [[nodiscard]]
    constexpr sparse_map(const sparse_map &) noexcept = delete;
 
    [[nodiscard]]
    constexpr sparse_map(sparse_map &&) noexcept = default;
 
    constexpr auto operator=(const sparse_map &) noexcept
        -> sparse_map & = delete;
 
    constexpr auto operator=(sparse_map &&) noexcept
        -> sparse_map & = default;
 
    constexpr ~sparse_map() noexcept final = default;
 
    template <typename ...Args>
    constexpr void insert(const Key key, Args &&...args) noexcept
    {
        if (_sparse.extend(key + 1, std::numeric_limits<Key>::max()) || _sparse[key] == std::numeric_limits<Key>::max()) {
            _sparse[key] = _keys.size();
            _keys.push(key);
            _values.push(std::forward<Args>(args)...);
        }
        else if constexpr (sizeof...(Args) == 1 && (std::is_assignable_v<T &, Args> && ...)) {
            (*this)[key] = (std::forward<Args>(args), ...);
        }
        else {
            std::destroy_at(_values.begin() + _sparse[key]);
            std::construct_at(_values.begin() + _sparse[key], std::forward<Args>(args)...);
        }
    }
 
    [[nodiscard]]
    constexpr auto size() const noexcept
    {
        return _keys.size();
    }
 
    [[nodiscard]]
    constexpr auto contains(const Key key) const noexcept
    {
        return key < _sparse.size() && _sparse[key] != std::numeric_limits<Key>::max();
    }
 
    [[nodiscard]]
    constexpr auto at(const Key key) const noexcept
    {
        return contains(key) ? _values.begin() + _sparse[key] : nullptr;
    }
 
    [[nodiscard]]
    constexpr auto at(const Key key) noexcept
    {
        return contains(key) ? _values.begin() + _sparse[key] : nullptr;
    }
 
    [[nodiscard]]
    constexpr auto operator[](const Key key) const noexcept
        -> const auto &
    {
        return _values[_sparse[key]];
    }
 
    [[nodiscard]]
    constexpr auto operator[](const Key key) noexcept
        -> auto &
    {
        return _values[_sparse[key]];
    }
 
    [[nodiscard]]
    constexpr auto values() const noexcept
    {
        return std::ranges::subrange{_values.begin(), _values.end()};
    }
 
    [[nodiscard]]
    constexpr auto values() noexcept
    {
        return std::ranges::subrange{_values.begin(), _values.end()};
    }
 
    [[nodiscard]]
    constexpr auto zip() const noexcept
    {
        return std::views::zip(std::ranges::subrange{static_cast<const Key *>(_keys.begin()), static_cast<const Key *>(_keys.end())}, values());
    }
 
    [[nodiscard]]
    constexpr auto zip() noexcept
    {
        return std::views::zip(std::ranges::subrange{static_cast<const Key *>(_keys.begin()), static_cast<const Key *>(_keys.end())}, values());
    }
 
    constexpr void erase(const Key key) noexcept final
    {
        if (!contains(key)) {
            return;
        }
 
        if (_sparse[key] != _keys.size() - 1) {
            _values[_sparse[key]] = std::move(*(_values.end() - 1));
            _keys[_sparse[key]] = *(_keys.end() - 1);
            _sparse[_keys[_sparse[key]]] = _sparse[key];
        }
 
        _sparse[key] = std::numeric_limits<Key>::max();
        _keys.pop();
        _values.pop();
    }
 
    constexpr void clear() noexcept final
    {
        _sparse.clear();
        _keys.clear();
        _values.clear();
    }
 
private:
    stack_vector<Key, Key> _sparse;
    stack_vector<T, Key> _values;
    stack_vector<Key, Key> _keys;
};
}
 
#endif