view.hpp

#ifndef ENTT_ENTITY_VIEW_HPP
#define ENTT_ENTITY_VIEW_HPP
 
#include <algorithm>
#include <array>
#include <iterator>
#include <tuple>
#include <type_traits>
#include <utility>
#include "../config/config.h"
#include "../core/iterator.hpp"
#include "../core/type_traits.hpp"
#include "component.hpp"
#include "entity.hpp"
#include "fwd.hpp"
#include "sparse_set.hpp"
#include "storage.hpp"
#include "utility.hpp"
 
namespace entt {
 
namespace internal {
 
template<typename Type, std::size_t Component, std::size_t Exclude>
class view_iterator final {
    using iterator_type = typename Type::const_iterator;
 
    [[nodiscard]] bool valid() const ENTT_NOEXCEPT {
        return ((Component != 0u) || (*it != tombstone))
               && std::apply([entt = *it](const auto *...curr) { return (curr->contains(entt) && ...); }, pools)
               && std::apply([entt = *it](const auto *...curr) { return (!curr->contains(entt) && ...); }, filter);
    }
 
public:
    using value_type = typename iterator_type::value_type;
    using pointer = typename iterator_type::pointer;
    using reference = typename iterator_type::reference;
    using difference_type = typename iterator_type::difference_type;
    using iterator_category = std::forward_iterator_tag;
 
    view_iterator() ENTT_NOEXCEPT = default;
 
    view_iterator(iterator_type curr, iterator_type to, std::array<const Type *, Component> all_of, std::array<const Type *, Exclude> none_of) ENTT_NOEXCEPT
        : it{curr},
          last{to},
          pools{all_of},
          filter{none_of} {
        if(it != last && !valid()) {
            ++(*this);
        }
    }
 
    view_iterator &operator++() ENTT_NOEXCEPT {
        while(++it != last && !valid()) {}
        return *this;
    }
 
    view_iterator operator++(int) ENTT_NOEXCEPT {
        view_iterator orig = *this;
        return ++(*this), orig;
    }
 
    [[nodiscard]] pointer operator->() const ENTT_NOEXCEPT {
        return &*it;
    }
 
    [[nodiscard]] reference operator*() const ENTT_NOEXCEPT {
        return *operator->();
    }
 
    template<typename LhsType, auto... LhsArgs, typename RhsType, auto... RhsArgs>
    friend bool operator==(const view_iterator<LhsType, LhsArgs...> &, const view_iterator<RhsType, RhsArgs...> &) ENTT_NOEXCEPT;
 
private:
    iterator_type it;
    iterator_type last;
    std::array<const Type *, Component> pools;
    std::array<const Type *, Exclude> filter;
};
 
template<typename LhsType, auto... LhsArgs, typename RhsType, auto... RhsArgs>
[[nodiscard]] bool operator==(const view_iterator<LhsType, LhsArgs...> &lhs, const view_iterator<RhsType, RhsArgs...> &rhs) ENTT_NOEXCEPT {
    return lhs.it == rhs.it;
}
 
template<typename LhsType, auto... LhsArgs, typename RhsType, auto... RhsArgs>
[[nodiscard]] bool operator!=(const view_iterator<LhsType, LhsArgs...> &lhs, const view_iterator<RhsType, RhsArgs...> &rhs) ENTT_NOEXCEPT {
    return !(lhs == rhs);
}
 
template<typename It, typename... Storage>
struct extended_view_iterator final {
    using difference_type = std::ptrdiff_t;
    using value_type = decltype(std::tuple_cat(std::make_tuple(*std::declval<It>()), std::declval<Storage>().get_as_tuple({})...));
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using iterator_category = std::input_iterator_tag;
 
    extended_view_iterator() = default;
 
    extended_view_iterator(It from, std::tuple<Storage *...> storage)
        : it{from},
          pools{storage} {}
 
    extended_view_iterator &operator++() ENTT_NOEXCEPT {
        return ++it, *this;
    }
 
    extended_view_iterator operator++(int) ENTT_NOEXCEPT {
        extended_view_iterator orig = *this;
        return ++(*this), orig;
    }
 
    [[nodiscard]] reference operator*() const ENTT_NOEXCEPT {
        return std::apply([entt = *it](auto *...curr) { return std::tuple_cat(std::make_tuple(entt), curr->get_as_tuple(entt)...); }, pools);
    }
 
    [[nodiscard]] pointer operator->() const ENTT_NOEXCEPT {
        return operator*();
    }
 
    template<typename... Lhs, typename... Rhs>
    friend bool operator==(const extended_view_iterator<Lhs...> &, const extended_view_iterator<Rhs...> &) ENTT_NOEXCEPT;
 
private:
    It it;
    std::tuple<Storage *...> pools;
};
 
template<typename... Lhs, typename... Rhs>
[[nodiscard]] bool operator==(const extended_view_iterator<Lhs...> &lhs, const extended_view_iterator<Rhs...> &rhs) ENTT_NOEXCEPT {
    return lhs.it == rhs.it;
}
 
template<typename... Lhs, typename... Rhs>
[[nodiscard]] bool operator!=(const extended_view_iterator<Lhs...> &lhs, const extended_view_iterator<Rhs...> &rhs) ENTT_NOEXCEPT {
    return !(lhs == rhs);
}
 
} // namespace internal
 
template<typename, typename, typename, typename>
class basic_view;
 
template<typename Entity, typename... Component, typename... Exclude>
class basic_view<Entity, get_t<Component...>, exclude_t<Exclude...>> {
    template<typename, typename, typename, typename>
    friend class basic_view;
 
    template<typename Comp>
    using storage_type = constness_as_t<typename storage_traits<Entity, std::remove_const_t<Comp>>::storage_type, Comp>;
 
    template<std::size_t... Index>
    [[nodiscard]] auto pools_to_array(std::index_sequence<Index...>) const ENTT_NOEXCEPT {
        std::size_t pos{};
        std::array<const base_type *, sizeof...(Component) - 1u> other{};
        (static_cast<void>(std::get<Index>(pools) == view ? void() : void(other[pos++] = std::get<Index>(pools))), ...);
        return other;
    }
 
    template<std::size_t Comp, std::size_t Other, typename... Args>
    [[nodiscard]] auto dispatch_get(const std::tuple<Entity, Args...> &curr) const {
        if constexpr(Comp == Other) {
            return std::forward_as_tuple(std::get<Args>(curr)...);
        } else {
            return std::get<Other>(pools)->get_as_tuple(std::get<0>(curr));
        }
    }
 
    template<std::size_t Comp, typename Func, std::size_t... Index>
    void each(Func func, std::index_sequence<Index...>) const {
        for(const auto curr: std::get<Comp>(pools)->each()) {
            const auto entt = std::get<0>(curr);
 
            if(((sizeof...(Component) != 1u) || (entt != tombstone))
               && ((Comp == Index || std::get<Index>(pools)->contains(entt)) && ...)
               && std::apply([entt](const auto *...cpool) { return (!cpool->contains(entt) && ...); }, filter)) {
                if constexpr(is_applicable_v<Func, decltype(std::tuple_cat(std::tuple<entity_type>{}, std::declval<basic_view>().get({})))>) {
                    std::apply(func, std::tuple_cat(std::make_tuple(entt), dispatch_get<Comp, Index>(curr)...));
                } else {
                    std::apply(func, std::tuple_cat(dispatch_get<Comp, Index>(curr)...));
                }
            }
        }
    }
 
    template<typename Func, std::size_t... Index>
    void pick_and_each(Func func, std::index_sequence<Index...> seq) const {
        ((std::get<Index>(pools) == view ? each<Index>(std::move(func), seq) : void()), ...);
    }
 
public:
    using entity_type = Entity;
    using size_type = std::size_t;
    using base_type = std::common_type_t<typename storage_type<Component>::base_type...>;
    using iterator = internal::view_iterator<base_type, sizeof...(Component) - 1u, sizeof...(Exclude)>;
    using iterable = iterable_adaptor<internal::extended_view_iterator<iterator, storage_type<Component>...>>;
 
    basic_view() ENTT_NOEXCEPT
        : pools{},
          filter{},
          view{} {}
 
    basic_view(storage_type<Component> &...component, const storage_type<Exclude> &...epool) ENTT_NOEXCEPT
        : pools{&component...},
          filter{&epool...},
          view{(std::min)({&static_cast<const base_type &>(component)...}, [](auto *lhs, auto *rhs) { return lhs->size() < rhs->size(); })} {}
 
    template<typename Comp>
    [[nodiscard]] basic_view use() const ENTT_NOEXCEPT {
        basic_view other{*this};
        other.view = std::get<storage_type<Comp> *>(pools);
        return other;
    }
 
    template<std::size_t Comp>
    [[nodiscard]] basic_view use() const ENTT_NOEXCEPT {
        basic_view other{*this};
        other.view = std::get<Comp>(pools);
        return other;
    }
 
    const base_type &handle() const ENTT_NOEXCEPT {
        return *view;
    }
 
    template<typename Comp>
    [[nodiscard]] decltype(auto) storage() const ENTT_NOEXCEPT {
        return *std::get<storage_type<Comp> *>(pools);
    }
 
    template<std::size_t Comp>
    [[nodiscard]] decltype(auto) storage() const ENTT_NOEXCEPT {
        return *std::get<Comp>(pools);
    }
 
    [[nodiscard]] size_type size_hint() const ENTT_NOEXCEPT {
        return view->size();
    }
 
    [[nodiscard]] iterator begin() const ENTT_NOEXCEPT {
        return iterator{view->begin(), view->end(), pools_to_array(std::index_sequence_for<Component...>{}), filter};
    }
 
    [[nodiscard]] iterator end() const ENTT_NOEXCEPT {
        return iterator{view->end(), view->end(), pools_to_array(std::index_sequence_for<Component...>{}), filter};
    }
 
    [[nodiscard]] entity_type front() const ENTT_NOEXCEPT {
        const auto it = begin();
        return it != end() ? *it : null;
    }
 
    [[nodiscard]] entity_type back() const ENTT_NOEXCEPT {
        auto it = view->rbegin();
        for(const auto last = view->rend(); it != last && !contains(*it); ++it) {}
        return it == view->rend() ? null : *it;
    }
 
    [[nodiscard]] iterator find(const entity_type entt) const ENTT_NOEXCEPT {
        return contains(entt) ? iterator{view->find(entt), view->end(), pools_to_array(std::index_sequence_for<Component...>{}), filter} : end();
    }
 
    [[nodiscard]] decltype(auto) operator[](const entity_type entt) const {
        return get<Component...>(entt);
    }
 
    [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
        return view != nullptr;
    }
 
    [[nodiscard]] bool contains(const entity_type entt) const ENTT_NOEXCEPT {
        return std::apply([entt](const auto *...curr) { return (curr->contains(entt) && ...); }, pools)
               && std::apply([entt](const auto *...curr) { return (!curr->contains(entt) && ...); }, filter);
    }
 
    template<typename... Comp>
    [[nodiscard]] decltype(auto) get(const entity_type entt) const {
        ENTT_ASSERT(contains(entt), "View does not contain entity");
 
        if constexpr(sizeof...(Comp) == 0) {
            return std::apply([entt](auto *...curr) { return std::tuple_cat(curr->get_as_tuple(entt)...); }, pools);
        } else if constexpr(sizeof...(Comp) == 1) {
            return (std::get<storage_type<Comp> *>(pools)->get(entt), ...);
        } else {
            return std::tuple_cat(std::get<storage_type<Comp> *>(pools)->get_as_tuple(entt)...);
        }
    }
 
    template<std::size_t First, std::size_t... Other>
    [[nodiscard]] decltype(auto) get(const entity_type entt) const {
        ENTT_ASSERT(contains(entt), "View does not contain entity");
 
        if constexpr(sizeof...(Other) == 0) {
            return std::get<First>(pools)->get(entt);
        } else {
            return std::tuple_cat(std::get<First>(pools)->get_as_tuple(entt), std::get<Other>(pools)->get_as_tuple(entt)...);
        }
    }
 
    template<typename Func>
    void each(Func func) const {
        pick_and_each(std::move(func), std::index_sequence_for<Component...>{});
    }
 
    [[nodiscard]] iterable each() const ENTT_NOEXCEPT {
        return {internal::extended_view_iterator{begin(), pools}, internal::extended_view_iterator{end(), pools}};
    }
 
    template<typename... Get, typename... Excl>
    [[nodiscard]] auto operator|(const basic_view<Entity, get_t<Get...>, exclude_t<Excl...>> &other) const ENTT_NOEXCEPT {
        using view_type = basic_view<Entity, get_t<Component..., Get...>, exclude_t<Exclude..., Excl...>>;
        return std::make_from_tuple<view_type>(std::tuple_cat(
            std::apply([](auto *...curr) { return std::forward_as_tuple(*curr...); }, pools),
            std::apply([](auto *...curr) { return std::forward_as_tuple(*curr...); }, other.pools),
            std::apply([](const auto *...curr) { return std::forward_as_tuple(static_cast<const storage_type<Exclude> &>(*curr)...); }, filter),
            std::apply([](const auto *...curr) { return std::forward_as_tuple(static_cast<const storage_type<Excl> &>(*curr)...); }, other.filter)));
    }
 
private:
    std::tuple<storage_type<Component> *...> pools;
    std::array<const base_type *, sizeof...(Exclude)> filter;
    const base_type *view;
};
 
template<typename Entity, typename Component>
class basic_view<Entity, get_t<Component>, exclude_t<>, std::void_t<std::enable_if_t<!component_traits<std::remove_const_t<Component>>::in_place_delete>>> {
    template<typename, typename, typename, typename>
    friend class basic_view;
 
    using storage_type = constness_as_t<typename storage_traits<Entity, std::remove_const_t<Component>>::storage_type, Component>;
 
public:
    using entity_type = Entity;
    using size_type = std::size_t;
    using base_type = typename storage_type::base_type;
    using iterator = typename base_type::iterator;
    using reverse_iterator = typename base_type::reverse_iterator;
    using iterable = decltype(std::declval<storage_type>().each());
 
    basic_view() ENTT_NOEXCEPT
        : pools{},
          filter{},
          view{} {}
 
    basic_view(storage_type &ref) ENTT_NOEXCEPT
        : pools{&ref},
          filter{},
          view{&ref} {}
 
    const base_type &handle() const ENTT_NOEXCEPT {
        return *view;
    }
 
    template<typename Comp = Component>
    [[nodiscard]] decltype(auto) storage() const ENTT_NOEXCEPT {
        static_assert(std::is_same_v<Comp, Component>, "Invalid component type");
        return *std::get<0>(pools);
    }
 
    template<std::size_t Comp>
    [[nodiscard]] decltype(auto) storage() const ENTT_NOEXCEPT {
        return *std::get<Comp>(pools);
    }
 
    [[nodiscard]] size_type size() const ENTT_NOEXCEPT {
        return view->size();
    }
 
    [[nodiscard]] bool empty() const ENTT_NOEXCEPT {
        return view->empty();
    }
 
    [[nodiscard]] iterator begin() const ENTT_NOEXCEPT {
        return view->begin();
    }
 
    [[nodiscard]] iterator end() const ENTT_NOEXCEPT {
        return view->end();
    }
 
    [[nodiscard]] reverse_iterator rbegin() const ENTT_NOEXCEPT {
        return view->rbegin();
    }
 
    [[nodiscard]] reverse_iterator rend() const ENTT_NOEXCEPT {
        return view->rend();
    }
 
    [[nodiscard]] entity_type front() const ENTT_NOEXCEPT {
        return empty() ? null : *begin();
    }
 
    [[nodiscard]] entity_type back() const ENTT_NOEXCEPT {
        return empty() ? null : *rbegin();
    }
 
    [[nodiscard]] iterator find(const entity_type entt) const ENTT_NOEXCEPT {
        return contains(entt) ? view->find(entt) : end();
    }
 
    [[nodiscard]] entity_type operator[](const size_type pos) const {
        return begin()[pos];
    }
 
    [[nodiscard]] decltype(auto) operator[](const entity_type entt) const {
        return get<Component>(entt);
    }
 
    [[nodiscard]] explicit operator bool() const ENTT_NOEXCEPT {
        return view != nullptr;
    }
 
    [[nodiscard]] bool contains(const entity_type entt) const ENTT_NOEXCEPT {
        return view->contains(entt);
    }
 
    template<typename... Comp>
    [[nodiscard]] decltype(auto) get(const entity_type entt) const {
        ENTT_ASSERT(contains(entt), "View does not contain entity");
 
        if constexpr(sizeof...(Comp) == 0) {
            return std::get<0>(pools)->get_as_tuple(entt);
        } else {
            static_assert(std::is_same_v<Comp..., Component>, "Invalid component type");
            return std::get<0>(pools)->get(entt);
        }
    }
 
    template<std::size_t Comp>
    [[nodiscard]] decltype(auto) get(const entity_type entt) const {
        ENTT_ASSERT(contains(entt), "View does not contain entity");
        return std::get<0>(pools)->get(entt);
    }
 
    template<typename Func>
    void each(Func func) const {
        if constexpr(is_applicable_v<Func, decltype(*each().begin())>) {
            for(const auto pack: each()) {
                std::apply(func, pack);
            }
        } else if constexpr(std::is_invocable_v<Func, Component &>) {
            for(auto &&component: *std::get<0>(pools)) {
                func(component);
            }
        } else if constexpr(std::is_invocable_v<Func, Entity>) {
            for(auto entity: *view) {
                func(entity);
            }
        } else {
            for(size_type pos{}, last = size(); pos < last; ++pos) {
                func();
            }
        }
    }
 
    [[nodiscard]] iterable each() const ENTT_NOEXCEPT {
        return std::get<0>(pools)->each();
    }
 
    template<typename... Get, typename... Excl>
    [[nodiscard]] auto operator|(const basic_view<Entity, get_t<Get...>, exclude_t<Excl...>> &other) const ENTT_NOEXCEPT {
        using view_type = basic_view<Entity, get_t<Component, Get...>, exclude_t<Excl...>>;
        return std::make_from_tuple<view_type>(std::tuple_cat(
            std::forward_as_tuple(*std::get<0>(pools)),
            std::apply([](auto *...curr) { return std::forward_as_tuple(*curr...); }, other.pools),
            std::apply([](const auto *...curr) { return std::forward_as_tuple(static_cast<const typename view_type::template storage_type<Excl> &>(*curr)...); }, other.filter)));
    }
 
private:
    std::tuple<storage_type *> pools;
    std::array<const base_type *, 0u> filter;
    const base_type *view;
};
 
template<typename... Storage>
basic_view(Storage &...storage) -> basic_view<std::common_type_t<typename Storage::entity_type...>, get_t<constness_as_t<typename Storage::value_type, Storage>...>, exclude_t<>>;
 
} // namespace entt
 
#endif