path: root/src/crepe/api/EventManager.h

#pragma once

#include <functional>
#include <memory>
#include <type_traits>
#include <typeindex>
#include <unordered_map>
#include <vector>

#include "Event.h"
#include "EventHandler.h"

/**
 * \class EventManager
 * \brief The EventManager class is responsible for managing the subscription, triggering, 
 * and queueing of events. It handles events and dispatches them to appropriate subscribers.
 */
class EventManager {
public:
	/**
     * \brief Deleted copy constructor to prevent copying of the EventManager instance.
     */
	EventManager(const EventManager &) = delete;

	/**
     * \brief Deleted copy assignment operator to prevent assignment of the EventManager instance.
     */
	const EventManager & operator=(const EventManager &) = delete;

	/**
     * \brief Get the singleton instance of the EventManager.
     * 
     * This method returns the unique instance of the EventManager, creating it on the first call.
     * 
     * \return Reference to the EventManager instance.
     */
	static EventManager & get_instance();

	/**
     * \brief Subscribe to an event.
     * 
     * This method allows the registration of a callback for a specific event type and channel.
     * 
     * \tparam EventType The type of the event to subscribe to.
     * \param callback The callback function to invoke when the event is triggered.
     * \param channel The channel number to subscribe to (default is 0).
     */
	template <typename EventType>
	void subscribe(EventHandler<EventType> && callback, int channel = 0);

	/**
     * \brief Unsubscribe from an event.
     * 
     * This method removes a previously registered callback from an event.
     * 
     * \tparam EventType The type of the event to unsubscribe from.
     * \param callback The callback function to remove from the subscription list.
     * \param channel The event ID to unsubscribe from.
     */
	template <typename EventType>
	void unsubscribe(const EventHandler<EventType> &, int channel);

	/**
     * \brief Trigger an event.
     * 
     * This method invokes the appropriate callback(s) for the specified event.
     * 
     * \tparam EventType The type of the event to trigger.
     * \param event The event data to pass to the callback.
     * \param channel The channel from which to trigger the event (default is 0).
     */
	template <typename EventType>
	void trigger_event(const EventType & event, int channel);

	/**
     * \brief Queue an event for later processing.
     * 
     * This method adds an event to the event queue, which will be processed in the 
     * dispatch_events function.
     * 
     * \tparam EventType The type of the event to queue.
     * \param event The event to queue.
     * \param channel The channel number for the event (default is 0).
     */
	template <typename EventType>
	void queue_event(EventType && event, int channel);

	/**
     * \brief Dispatch all queued events.
     * 
     * This method processes all events in the event queue and triggers the corresponding 
     * callbacks for each event.
     */
	void dispatch_events();

private:
	/**
     * \brief Default constructor for the EventManager.
     * 
     * This constructor is private to enforce the singleton pattern.
     */
	EventManager() = default;

	//! The queue of events to be processed.
	std::vector<std::tuple<std::unique_ptr<Event>, int, std::type_index>>
		events_queue;
	//! Registered event handlers.
	std::unordered_map<std::type_index,
					   std::vector<std::unique_ptr<IEventHandlerWrapper>>>
		subscribers;
	//! Event handlers indexed by event ID.
	std::unordered_map<
		std::type_index,
		std::unordered_map<int,
						   std::vector<std::unique_ptr<IEventHandlerWrapper>>>>
		subscribers_by_event_id;
};
template <typename EventType>
void EventManager::subscribe(EventHandler<EventType> && callback, int channel) {
	std::type_index event_type = typeid(EventType);
	std::unique_ptr<EventHandlerWrapper<EventType>> handler
		= std::make_unique<EventHandlerWrapper<EventType>>(callback);

	if (channel) {
		std::unordered_map<int,
						   std::vector<std::unique_ptr<IEventHandlerWrapper>>> &
			handlers_map
			= this->subscribers_by_event_id[event_type];
		std::unordered_map<
			int, std::vector<std::unique_ptr<IEventHandlerWrapper>>>::iterator
			handlers
			= handlers_map.find(channel);
		if (handlers != handlers_map.end()) {
			handlers->second.emplace_back(std::move(handler));
		} else {
			handlers_map[channel].emplace_back(std::move(handler));
		}
	} else {
		std::vector<std::unique_ptr<IEventHandlerWrapper>> & handlers
			= this->subscribers[event_type];
		handlers.emplace_back(std::move(handler));
	}
}

template <typename EventType>
void EventManager::queue_event(EventType && event, int channel) {
	std::type_index event_type = std::type_index(typeid(EventType));

	std::unique_ptr<EventType> event_ptr
		= std::make_unique<EventType>(std::forward<EventType>(event));

	std::tuple<std::unique_ptr<Event>, int, std::type_index> tuple(
		std::move(event_ptr), channel, event_type);
	this->events_queue.push_back(std::move(tuple));
}

template <typename EventType>
void EventManager::trigger_event(const EventType & event, int channel) {
	std::type_index event_type = std::type_index(typeid(EventType));

	if (channel > 0) {
		std::unordered_map<int,
						   std::vector<std::unique_ptr<IEventHandlerWrapper>>> &
			handlers_map
			= this->subscribers_by_event_id[event_type];
		std::unordered_map<
			int, std::vector<std::unique_ptr<IEventHandlerWrapper>>>::iterator
			handlers_it
			= handlers_map.find(channel);

		if (handlers_it != handlers_map.end()) {
			std::vector<std::unique_ptr<IEventHandlerWrapper>> & handlers
				= handlers_it->second;
			for (std::vector<std::unique_ptr<IEventHandlerWrapper>>::iterator it
				 = handlers.begin();
				 it != handlers.end();) {
				// erases callback if callback function returns true
				if ((*it)->exec(event)) {
					it = handlers.erase(it);
				} else {
					++it;
				}
			}
		}
	} else {
		std::vector<std::unique_ptr<IEventHandlerWrapper>> & handlers
			= this->subscribers[event_type];
		for (std::vector<std::unique_ptr<IEventHandlerWrapper>>::iterator it
			 = handlers.begin();
			 it != handlers.end();) {
			// erases callback if callback function returns true
			if ((*it)->exec(event)) {
				it = handlers.erase(it);
			} else {
				++it;
			}
		}
	}
}

template <typename EventType>
void EventManager::unsubscribe(const EventHandler<EventType> & callback,
							   int channel) {
	std::type_index event_type(typeid(EventType));
	std::string handler_name = callback.target_type().name();

	if (channel) {
		std::unordered_map<
			std::type_index,
			std::unordered_map<
				int, std::vector<std::unique_ptr<IEventHandlerWrapper>>>>::
			iterator subscriber_list
			= this->subscribers_by_event_id.find(event_type);
		if (subscriber_list != this->subscribers_by_event_id.end()) {
			std::unordered_map<
				int, std::vector<std::unique_ptr<IEventHandlerWrapper>>> &
				handlers_map
				= subscriber_list->second;
			std::unordered_map<
				int,
				std::vector<std::unique_ptr<IEventHandlerWrapper>>>::iterator
				handlers
				= handlers_map.find(channel);
			if (handlers != handlers_map.end()) {
				std::vector<std::unique_ptr<IEventHandlerWrapper>> & callbacks
					= handlers->second;
				for (std::vector<
						 std::unique_ptr<IEventHandlerWrapper>>::iterator it
					 = callbacks.begin();
					 it != callbacks.end(); ++it) {
					if ((*it)->get_type() == handler_name) {
						it = callbacks.erase(it);
						return;
					}
				}
			}
		}
	} else {
		std::unordered_map<std::type_index,
						   std::vector<std::unique_ptr<IEventHandlerWrapper>>>::
			iterator handlers_it
			= this->subscribers.find(event_type);
		if (handlers_it != this->subscribers.end()) {
			std::vector<std::unique_ptr<IEventHandlerWrapper>> & handlers
				= handlers_it->second;
			for (std::vector<std::unique_ptr<IEventHandlerWrapper>>::iterator it
				 = handlers.begin();
				 it != handlers.end(); ++it) {
				if ((*it)->get_type() == handler_name) {
					it = handlers.erase(it);
					return;
				}
			}
		}
	}
}