observer.hpp

#ifndef ENTT_ENTITY_OBSERVER_HPP
#define ENTT_ENTITY_OBSERVER_HPP
 
#include <cstddef>
#include <cstdint>
#include <limits>
#include <type_traits>
#include <utility>
#include "../config/config.h"
#include "../core/type_traits.hpp"
#include "../signal/delegate.hpp"
#include "entity.hpp"
#include "fwd.hpp"
#include "registry.hpp"
#include "storage.hpp"
#include "utility.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...> = {}) ENTT_NOEXCEPT {
        return basic_collector<matcher<type_list<>, type_list<>, type_list<NoneOf...>, AllOf...>>{};
    }
 
    template<typename AnyOf>
    static constexpr auto update() ENTT_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...> = {}) ENTT_NOEXCEPT {
        return basic_collector<matcher<type_list<>, type_list<>, type_list<NoneOf...>, AllOf...>, current_type, Other...>{};
    }
 
    template<typename AnyOf>
    static constexpr auto update() ENTT_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...> = {}) ENTT_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 Entity>
class basic_observer {
    using payload_type = std::uint32_t;
 
    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, basic_registry<Entity> &reg, const Entity entt) {
            if(reg.template all_of<Require...>(entt) && !reg.template any_of<Reject...>(entt)) {
                if(!obs.storage.contains(entt)) {
                    obs.storage.emplace(entt);
                }
 
                obs.storage.get(entt) |= (1 << Index);
            }
        }
 
        template<std::size_t Index>
        static void discard_if(basic_observer &obs, basic_registry<Entity> &, const Entity entt) {
            if(obs.storage.contains(entt) && !(obs.storage.get(entt) &= (~(1 << Index)))) {
                obs.storage.erase(entt);
            }
        }
 
        template<std::size_t Index>
        static void connect(basic_observer &obs, basic_registry<Entity> &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, basic_registry<Entity> &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, basic_registry<Entity> &reg, const Entity 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.storage.contains(entt)) {
                    obs.storage.emplace(entt);
                }
 
                obs.storage.get(entt) |= (1 << Index);
            }
        }
 
        template<std::size_t Index>
        static void discard_if(basic_observer &obs, basic_registry<Entity> &, const Entity entt) {
            if(obs.storage.contains(entt) && !(obs.storage.get(entt) &= (~(1 << Index)))) {
                obs.storage.erase(entt);
            }
        }
 
        template<std::size_t Index>
        static void connect(basic_observer &obs, basic_registry<Entity> &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, basic_registry<Entity> &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(basic_registry<Entity> &reg, basic_observer &obs) {
        (matcher_handler<Matcher>::disconnect(obs, reg), ...);
    }
 
    template<typename... Matcher, std::size_t... Index>
    void connect(basic_registry<Entity> &reg, std::index_sequence<Index...>) {
        static_assert(sizeof...(Matcher) < std::numeric_limits<payload_type>::digits, "Too many matchers");
        (matcher_handler<Matcher>::template connect<Index>(*this, reg), ...);
        release.template connect<&basic_observer::disconnect<Matcher...>>(reg);
    }
 
public:
    using entity_type = Entity;
    using size_type = std::size_t;
    using iterator = typename basic_sparse_set<Entity>::iterator;
 
    basic_observer()
        : release{},
          storage{} {}
 
    basic_observer(const basic_observer &) = delete;
    basic_observer(basic_observer &&) = delete;
 
    template<typename... Matcher>
    basic_observer(basic_registry<entity_type> &reg, basic_collector<Matcher...>)
        : basic_observer{} {
        connect<Matcher...>(reg, std::index_sequence_for<Matcher...>{});
    }
 
    ~basic_observer() = default;
 
    basic_observer &operator=(const basic_observer &) = delete;
 
    basic_observer &operator=(basic_observer &&) = delete;
 
    template<typename... Matcher>
    void connect(basic_registry<entity_type> &reg, basic_collector<Matcher...>) {
        disconnect();
        connect<Matcher...>(reg, std::index_sequence_for<Matcher...>{});
        storage.clear();
    }
 
    void disconnect() {
        if(release) {
            release(*this);
            release.reset();
        }
    }
 
    [[nodiscard]] size_type size() const ENTT_NOEXCEPT {
        return storage.size();
    }
 
    [[nodiscard]] bool empty() const ENTT_NOEXCEPT {
        return storage.empty();
    }
 
    [[nodiscard]] const entity_type *data() const ENTT_NOEXCEPT {
        return storage.data();
    }
 
    [[nodiscard]] iterator begin() const ENTT_NOEXCEPT {
        return storage.basic_sparse_set<entity_type>::begin();
    }
 
    [[nodiscard]] iterator end() const ENTT_NOEXCEPT {
        return storage.basic_sparse_set<entity_type>::end();
    }
 
    void clear() ENTT_NOEXCEPT {
        storage.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;
    basic_storage<entity_type, payload_type> storage;
};
 
} // namespace entt
 
#endif