cocos_lib/cocos/core/event/EventBus.h

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#pragma once

#include <cstddef>
#include <iostream>
#include <memory>
#include <type_traits>

#include "base/Log.h"
#include "base/std/container/vector.h"
#include "core/memop/Pool.h"
#include "intl/EventIntl.h"
#include "intl/List.h"

namespace cc {
namespace event {
class BusEventListenerBase;

template <typename EHandler>
class BusEventListenerDB;

template <typename EHandler, typename... ARGS>
class BusEventBroadcaster;

class BusEventListenerContainer;
struct BusEventListenerEntry {
    BusEventListenerEntry *next{nullptr};
    BusEventListenerEntry *prev{nullptr};
    BusEventListenerBase *listener{nullptr};
};
class BusEventListenerBase {
protected:
    BusEventListenerEntry *entry{nullptr}; // NOLINT
    friend class BusEventListenerContainer;
};

class BusEventListenerContainer {
public:
    template <typename EHandler, typename... ARGS>
    bool broadcast(ARGS &&...args);

protected:
    BusEventListenerContainer() = default;
    virtual ~BusEventListenerContainer() = default;
    void addListener(BusEventListenerBase *);
    void removeListener(BusEventListenerBase *);

    bool hasPendingListeners() const {
        return !_listenersToRemove.empty() || _listenersToAdd;
    }
    void addOrRemovePendingListeners();
    // fields
    BusEventListenerEntry *_listenerList{nullptr};
    BusEventListenerEntry *_listenersToAdd{nullptr};
    ccstd::vector<BusEventListenerEntry *> _listenersToRemove;
    int _isBroadcasting = 0;

    template <typename T>
    friend class BusEventListenerDB;

    template <typename EHandler, typename... ARGS>
    friend class BusEventBroadcaster;

    friend class BusEventListenerBase;
    template <typename E>
    friend class Listener;
};

template <typename EHandler, typename... ARGS>
class BusEventBroadcaster final : public BusEventListenerContainer {
public:
    bool doBroadcast(ARGS &&...args);
};

template <typename EHandler, typename... ARGS>
bool BusEventListenerContainer::broadcast(ARGS &&...args) {
    using BusType = BusEventBroadcaster<EHandler, ARGS...>;
    _isBroadcasting++;
    auto ret = static_cast<BusType *>(this)->doBroadcast(std::forward<ARGS>(args)...);
    _isBroadcasting--;
    if (!_isBroadcasting && hasPendingListeners()) {
        addOrRemovePendingListeners();
    }
    return false;
}

template <typename EHandler>
class BusEventListenerDB final {
public:
    static BusEventListenerContainer *container() {
        if (ctn == nullptr) {
            ctn = new BusEventListenerContainer;
        }
        return ctn;
    }

private:
    static BusEventListenerContainer *ctn;
};

template <typename EHandler>
BusEventListenerContainer *BusEventListenerDB<EHandler>::ctn = nullptr;

template <typename BusType, typename R, typename... ARGS>
struct BusEventTrait {
    using _bus_type = BusType;
    using _return_type = R;
    using _argument_tuple_types = std::tuple<ARGS...>;
    constexpr static int ARG_COUNT = sizeof...(ARGS);
};
/**
 * Bus Event Listener
 */
template <typename EHandler>
class Listener : public BusEventListenerBase {
public:
    using _agurment_tuple_types = typename EHandler::_argument_tuple_types;
    using _argument_wrapper = typename intl::TupleExtractor<_agurment_tuple_types>;
    // using func_type = typename _argument_wrapper::func_type;
    using _std_func_type = typename _argument_wrapper::std_func_type;

    constexpr static const char *BUS_NAME = EHandler::BUS_NAME;
    constexpr static const char *HANDLE_CLASS = EHandler::HANDLE_CLASS;

    Listener();
    ~Listener();

    inline bool isEnabled() const { return _enabled; }
    inline void enable() { _enabled = true; }
    inline void disable() { _enabled = false; }
    inline void reset() { _callback = nullptr; }

    template <typename Fn>
    bool bind(Fn &&func) {
        _callback = intl::convertLambda(std::forward<Fn>(func));
        return true;
    }

    template <typename... ARGS>
    void invoke(ARGS &&...args) {
        if (_callback && _enabled) {
            _callback(std::forward<ARGS>(args)...);
        } else {
            CC_LOG_DEBUG("EventBus[%s] has no listener found!", BUS_NAME);
        }
    }

    const char *getBusName() const { return BUS_NAME; }
    const char *getHandlerName() const { return HANDLE_CLASS; }

private:
    bool _enabled{true};
    _std_func_type _callback;

    friend class BusEventListenerContainer;
};

template <typename EHandler>
Listener<EHandler>::Listener() {
    entry = new BusEventListenerEntry;
    entry->listener = this;
    BusEventListenerDB<EHandler>::container()->addListener(this);
}

template <typename EHandler>
Listener<EHandler>::~Listener() {
    BusEventListenerDB<EHandler>::container()->removeListener(this);
}

template <typename EHandler, typename... ARGS>
bool BusEventBroadcaster<EHandler, ARGS...>::doBroadcast(ARGS &&...args) {
    // broadcast events to all listeners
    EVENT_LIST_LOOP_BEGIN(curr, _listenerList)
    if (curr->listener) {
        static_cast<Listener<EHandler> *>(curr->listener)->invoke(std::forward<ARGS>(args)...);
    }
    EVENT_LIST_LOOP_END(curr, _listenerList)
    return true;
}

template <typename EHandler, typename... ARGS>
void broadcast(ARGS &&...args) {
    static_assert(sizeof...(ARGS) == EHandler::ARG_COUNT, "parameter count incorrect");
    event::intl::validateParameters<0, EHandler, ARGS...>(std::forward<ARGS>(args)...);
    auto *listenerSet = BusEventListenerDB<EHandler>::container();
    listenerSet->template broadcast<EHandler, ARGS...>(std::forward<ARGS>(args)...);
}

} // namespace event
} // namespace cc

// NOLINTNEXTLINE
#define EventBusName_(n) n##_ebus

#define DECLARE_EVENT_BUS(EventBusClass)                        \
    struct EventBusClass##_ebus {                               \
        constexpr static const char *BUS_NAME = #EventBusClass; \
    };

// NOLINTNEXTLINE
#define _DECLARE_BUS_EVENT_VA(BusEventClass, EventBusClass, ...)                                             \
    struct BusEventClass final : cc::event::BusEventTrait<EventBusName_(EventBusClass), void, __VA_ARGS__> { \
        using BusType = EventBusName_(EventBusClass);                                                        \
        using Listener = cc::event::Listener<BusEventClass>;                                                 \
        constexpr static const char *BUS_NAME = BusType::BUS_NAME;                                           \
        constexpr static const char *HANDLE_CLASS = #BusEventClass;                                          \
        constexpr static size_t TypeID() {                                                                   \
            return cc::event::intl::hash(#BusEventClass);                                                    \
        }                                                                                                    \
        template <typename... ARGS>                                                                          \
        static inline void emit(ARGS &&...args) {                                                            \
            cc::event::emit<BusEventClass>(std::forward<ARGS>(args)...);                                     \
        }                                                                                                    \
    };

#include "intl/EventBusMacros.h"