observer.hpp

#ifndef ENTT_ENTITY_OBSERVER_HPP
#define ENTT_ENTITY_OBSERVER_HPP
 
#include <cstddef>
#include <cstdint>
#include <limits>
#include <type_traits>
#include <utility>
#include "../core/type_traits.hpp"
#include "../signal/delegate.hpp"
#include "fwd.hpp"
#include "storage.hpp"
 
namespace entt {
 
template<typename...>
struct matcher {};
 
template<typename...>
struct basic_collector;
 
template<>
struct basic_collector<> {
    template<typename... AllOf, typename... NoneOf>
    static constexpr auto group(exclude_t<NoneOf...> = exclude_t{}) noexcept {
        return basic_collector<matcher<type_list<>, type_list<>, type_list<NoneOf...>, AllOf...>>{};
    }
 
    template<typename AnyOf>
    static constexpr auto update() noexcept {
        return basic_collector<matcher<type_list<>, type_list<>, AnyOf>>{};
    }
};
 
template<typename... Reject, typename... Require, typename... Rule, typename... Other>
struct basic_collector<matcher<type_list<Reject...>, type_list<Require...>, Rule...>, Other...> {
    using current_type = matcher<type_list<Reject...>, type_list<Require...>, Rule...>;
 
    template<typename... AllOf, typename... NoneOf>
    static constexpr auto group(exclude_t<NoneOf...> = exclude_t{}) noexcept {
        return basic_collector<matcher<type_list<>, type_list<>, type_list<NoneOf...>, AllOf...>, current_type, Other...>{};
    }
 
    template<typename AnyOf>
    static constexpr auto update() noexcept {
        return basic_collector<matcher<type_list<>, type_list<>, AnyOf>, current_type, Other...>{};
    }
 
    template<typename... AllOf, typename... NoneOf>
    static constexpr auto where(exclude_t<NoneOf...> = exclude_t{}) noexcept {
        using extended_type = matcher<type_list<Reject..., NoneOf...>, type_list<Require..., AllOf...>, Rule...>;
        return basic_collector<extended_type, Other...>{};
    }
};
 
inline constexpr basic_collector<> collector{};
 
template<typename Registry, typename Mask, typename Allocator>
class basic_observer: private basic_storage<Mask, typename Registry::entity_type, Allocator> {
    using base_type = basic_storage<Mask, typename Registry::entity_type, Allocator>;
 
    template<typename>
    struct matcher_handler;
 
    template<typename... Reject, typename... Require, typename AnyOf>
    struct matcher_handler<matcher<type_list<Reject...>, type_list<Require...>, AnyOf>> {
        template<std::size_t Index>
        static void maybe_valid_if(basic_observer &obs, Registry &reg, const typename Registry::entity_type entt) {
            if(reg.template all_of<Require...>(entt) && !reg.template any_of<Reject...>(entt)) {
                if(!obs.contains(entt)) {
                    obs.emplace(entt);
                }
 
                obs.get(entt) |= (1 << Index);
            }
        }
 
        template<std::size_t Index>
        static void discard_if(basic_observer &obs, Registry &, const typename Registry::entity_type entt) {
            if(obs.contains(entt) && !(obs.get(entt) &= (~(1 << Index)))) {
                obs.erase(entt);
            }
        }
 
        template<std::size_t Index>
        static void connect(basic_observer &obs, Registry &reg) {
            (reg.template on_destroy<Require>().template connect<&discard_if<Index>>(obs), ...);
            (reg.template on_construct<Reject>().template connect<&discard_if<Index>>(obs), ...);
            reg.template on_update<AnyOf>().template connect<&maybe_valid_if<Index>>(obs);
            reg.template on_destroy<AnyOf>().template connect<&discard_if<Index>>(obs);
        }
 
        static void disconnect(basic_observer &obs, Registry &reg) {
            (reg.template on_destroy<Require>().disconnect(&obs), ...);
            (reg.template on_construct<Reject>().disconnect(&obs), ...);
            reg.template on_update<AnyOf>().disconnect(&obs);
            reg.template on_destroy<AnyOf>().disconnect(&obs);
        }
    };
 
    template<typename... Reject, typename... Require, typename... NoneOf, typename... AllOf>
    struct matcher_handler<matcher<type_list<Reject...>, type_list<Require...>, type_list<NoneOf...>, AllOf...>> {
        template<std::size_t Index, typename... Ignore>
        static void maybe_valid_if(basic_observer &obs, Registry &reg, const typename Registry::entity_type entt) {
            auto condition = [&reg, entt]() {
                if constexpr(sizeof...(Ignore) == 0) {
                    return reg.template all_of<AllOf..., Require...>(entt) && !reg.template any_of<NoneOf..., Reject...>(entt);
                } else {
                    return reg.template all_of<AllOf..., Require...>(entt) && ((std::is_same_v<Ignore..., NoneOf> || !reg.template any_of<NoneOf>(entt)) && ...) && !reg.template any_of<Reject...>(entt);
                }
            };
 
            if(condition()) {
                if(!obs.contains(entt)) {
                    obs.emplace(entt);
                }
 
                obs.get(entt) |= (1 << Index);
            }
        }
 
        template<std::size_t Index>
        static void discard_if(basic_observer &obs, Registry &, const typename Registry::entity_type entt) {
            if(obs.contains(entt) && !(obs.get(entt) &= (~(1 << Index)))) {
                obs.erase(entt);
            }
        }
 
        template<std::size_t Index>
        static void connect(basic_observer &obs, Registry &reg) {
            (reg.template on_destroy<Require>().template connect<&discard_if<Index>>(obs), ...);
            (reg.template on_construct<Reject>().template connect<&discard_if<Index>>(obs), ...);
            (reg.template on_construct<AllOf>().template connect<&maybe_valid_if<Index>>(obs), ...);
            (reg.template on_destroy<NoneOf>().template connect<&maybe_valid_if<Index, NoneOf>>(obs), ...);
            (reg.template on_destroy<AllOf>().template connect<&discard_if<Index>>(obs), ...);
            (reg.template on_construct<NoneOf>().template connect<&discard_if<Index>>(obs), ...);
        }
 
        static void disconnect(basic_observer &obs, Registry &reg) {
            (reg.template on_destroy<Require>().disconnect(&obs), ...);
            (reg.template on_construct<Reject>().disconnect(&obs), ...);
            (reg.template on_construct<AllOf>().disconnect(&obs), ...);
            (reg.template on_destroy<NoneOf>().disconnect(&obs), ...);
            (reg.template on_destroy<AllOf>().disconnect(&obs), ...);
            (reg.template on_construct<NoneOf>().disconnect(&obs), ...);
        }
    };
 
    template<typename... Matcher>
    static void disconnect(Registry &reg, basic_observer &obs) {
        (matcher_handler<Matcher>::disconnect(obs, reg), ...);
    }
 
    template<typename... Matcher, std::size_t... Index>
    void connect(Registry &reg, std::index_sequence<Index...>) {
        static_assert(sizeof...(Matcher) < std::numeric_limits<typename base_type::value_type>::digits, "Too many matchers");
        (matcher_handler<Matcher>::template connect<Index>(*this, reg), ...);
        release.template connect<&basic_observer::disconnect<Matcher...>>(reg);
    }
 
public:
    using registry_type = Registry;
    using entity_type = typename registry_type::entity_type;
    using size_type = std::size_t;
    using allocator_type = Allocator;
    using iterator = typename registry_type::common_type::iterator;
 
    basic_observer()
        : basic_observer{allocator_type{}} {}
 
    explicit basic_observer(const allocator_type &allocator)
        : base_type{allocator},
          release{} {}
 
    basic_observer(const basic_observer &) = delete;
 
    basic_observer(basic_observer &&) = delete;
 
    template<typename... Matcher>
    basic_observer(registry_type &reg, basic_collector<Matcher...>, const allocator_type &allocator = allocator_type{})
        : basic_observer{allocator} {
        connect<Matcher...>(reg, std::index_sequence_for<Matcher...>{});
    }
 
    basic_observer &operator=(const basic_observer &) = delete;
 
    basic_observer &operator=(basic_observer &&) = delete;
 
    template<typename... Matcher>
    void connect(registry_type &reg, basic_collector<Matcher...>) {
        disconnect();
        connect<Matcher...>(reg, std::index_sequence_for<Matcher...>{});
        base_type::clear();
    }
 
    void disconnect() {
        if(release) {
            release(*this);
            release.reset();
        }
    }
 
    [[nodiscard]] size_type size() const noexcept {
        return base_type::size();
    }
 
    [[nodiscard]] bool empty() const noexcept {
        return base_type::empty();
    }
 
    [[nodiscard]] const entity_type *data() const noexcept {
        return base_type::data();
    }
 
    [[nodiscard]] iterator begin() const noexcept {
        return base_type::base_type::begin();
    }
 
    [[nodiscard]] iterator end() const noexcept {
        return base_type::base_type::end();
    }
 
    void clear() noexcept {
        base_type::clear();
    }
 
    template<typename Func>
    void each(Func func) const {
        for(const auto entity: *this) {
            func(entity);
        }
    }
 
    template<typename Func>
    void each(Func func) {
        std::as_const(*this).each(std::move(func));
        clear();
    }
 
private:
    delegate<void(basic_observer &)> release;
};
 
} // namespace entt
 
#endif