runtime_view.hpp

#ifndef ENTT_ENTITY_RUNTIME_VIEW_HPP
#define ENTT_ENTITY_RUNTIME_VIEW_HPP


#include <iterator>
#include <cassert>
#include <vector>
#include <utility>
#include <algorithm>
#include <type_traits>
#include "../config/config.h"
#include "sparse_set.hpp"
#include "entity.hpp"
#include "fwd.hpp"


namespace entt {


template<typename Entity>
class basic_runtime_view {
    friend class basic_registry<Entity>;

    using underlying_iterator_type = typename sparse_set<Entity>::iterator_type;
    using traits_type = entt_traits<std::underlying_type_t<Entity>>;

    class iterator {
        friend class basic_runtime_view<Entity>;

        iterator(underlying_iterator_type first, underlying_iterator_type last, const sparse_set<Entity> * const *others, const sparse_set<Entity> * const *length) ENTT_NOEXCEPT
            : begin{first},
              end{last},
              from{others},
              to{length}
        {
            if(begin != end && !valid()) {
                ++(*this);
            }
        }

        bool valid() const ENTT_NOEXCEPT {
            return std::all_of(from, to, [entt = *begin](const auto *view) {
                return view->has(entt);
            });
        }

    public:
        using difference_type = typename underlying_iterator_type::difference_type;
        using value_type = typename underlying_iterator_type::value_type;
        using pointer = typename underlying_iterator_type::pointer;
        using reference = typename underlying_iterator_type::reference;
        using iterator_category = std::forward_iterator_tag;

        iterator() ENTT_NOEXCEPT = default;

        iterator & operator++() ENTT_NOEXCEPT {
            return (++begin != end && !valid()) ? ++(*this) : *this;
        }

        iterator operator++(int) ENTT_NOEXCEPT {
            iterator orig = *this;
            return ++(*this), orig;
        }

        bool operator==(const iterator &other) const ENTT_NOEXCEPT {
            return other.begin == begin;
        }

        bool operator!=(const iterator &other) const ENTT_NOEXCEPT {
            return !(*this == other);
        }

        pointer operator->() const ENTT_NOEXCEPT {
            return begin.operator->();
        }

        reference operator*() const ENTT_NOEXCEPT {
            return *operator->();
        }

    private:
        underlying_iterator_type begin;
        underlying_iterator_type end;
        const sparse_set<Entity> * const *from;
        const sparse_set<Entity> * const *to;
    };

    basic_runtime_view(std::vector<const sparse_set<Entity> *> others) ENTT_NOEXCEPT
        : pools{std::move(others)}
    {
        const auto it = std::min_element(pools.begin(), pools.end(), [](const auto *lhs, const auto *rhs) {
            return (!lhs && rhs) || (lhs && rhs && lhs->size() < rhs->size());
        });

        // brings the best candidate (if any) on front of the vector
        std::rotate(pools.begin(), it, pools.end());
    }

    bool valid() const ENTT_NOEXCEPT {
        return !pools.empty() && pools.front();
    }

public:
    using entity_type = typename sparse_set<Entity>::entity_type;
    using size_type = typename sparse_set<Entity>::size_type;
    using iterator_type = iterator;

    size_type size() const ENTT_NOEXCEPT {
        return valid() ? pools.front()->size() : size_type{};
    }

    bool empty() const ENTT_NOEXCEPT {
        return !valid() || pools.front()->empty();
    }

    iterator_type begin() const ENTT_NOEXCEPT {
        iterator_type it{};

        if(valid()) {
            const auto &pool = *pools.front();
            const auto * const *data = pools.data();
            it = { pool.begin(), pool.end(), data + 1, data + pools.size() };
        }

        return it;
    }

    iterator_type end() const ENTT_NOEXCEPT {
        iterator_type it{};

        if(valid()) {
            const auto &pool = *pools.front();
            it = { pool.end(), pool.end(), nullptr, nullptr };
        }

        return it;
    }

    bool contains(const entity_type entt) const ENTT_NOEXCEPT {
        return valid() && std::all_of(pools.cbegin(), pools.cend(), [entt](const auto *view) {
            return view->find(entt) != view->end();
        });
    }

    template<typename Func>
    void each(Func func) const {
        std::for_each(begin(), end(), func);
    }

private:
    std::vector<const sparse_set<Entity> *> pools;
};


}


#endif // ENTT_ENTITY_RUNTIME_VIEW_HPP