event_aggregator.h

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#pragma once
#include <functional>
#include <stdexcept>
 
#include "event_message.h"
#include <memory>
 
namespace hgps {
 
struct EventHandlerIdentifier {
    EventHandlerIdentifier() = delete;
 
    EventHandlerIdentifier(std::string identifier) : identifier_{identifier} {
        if (identifier.empty()) {
            throw std::invalid_argument("Event handler identifier must not be empty.");
        }
    }
 
    const std::string str() const noexcept { return identifier_; }
 
    auto operator<=>(const EventHandlerIdentifier &other) const = default;
 
  private:
    std::string identifier_;
};
 
class EventSubscriber {
  public:
    EventSubscriber() = default;
 
    EventSubscriber(const EventSubscriber &) = delete;
    EventSubscriber(EventSubscriber &&) = delete;
    EventSubscriber &operator=(const EventSubscriber &) = delete;
    EventSubscriber &operator=(EventSubscriber &&) = delete;
 
    virtual ~EventSubscriber() = default;
 
    virtual void unsubscribe() const = 0;
 
    [[nodiscard]] virtual EventHandlerIdentifier id() const noexcept = 0;
};
 
class EventAggregator {
  public:
    EventAggregator() = default;
 
    EventAggregator(EventAggregator &&other) = default;
 
    EventAggregator &operator=(EventAggregator &&other) = default;
 
    EventAggregator(const EventAggregator &) = delete;
    EventAggregator &operator=(const EventAggregator &) = delete;
 
    virtual ~EventAggregator() = default;
 
    [[nodiscard]] virtual std::unique_ptr<EventSubscriber>
    subscribe(EventType event_id,
              std::function<void(std::shared_ptr<EventMessage> message)> handler) = 0;
 
    virtual bool unsubscribe(const EventSubscriber &subscriber) = 0;
 
    virtual void publish(std::unique_ptr<EventMessage> message) const = 0;
 
    virtual void publish_async(std::unique_ptr<EventMessage> message) const = 0;
};
 
} // namespace hgps