/********************************************************************************
 * Copyright (C) 2014-2017 GSI Helmholtzzentrum fuer Schwerionenforschung GmbH  *
 *                                                                              *
 *              This software is distributed under the terms of the             *
 *              GNU Lesser General Public Licence (LGPL) version 3,             *
 *                  copied verbatim in the file "LICENSE"                       *
 ********************************************************************************/

#ifndef FAIR_MQ_EVENTMANAGER_H
#define FAIR_MQ_EVENTMANAGER_H

#include <memory>
#include <mutex>
#include <string>
#include <tuple>
#include <typeindex>
#include <typeinfo>
#include <unordered_map>
#include <utility>
#include <vector>

#include <boost/any.hpp>
#include <boost/functional/hash.hpp>
#include <boost/signals2.hpp>

namespace fair
{
namespace mq
{

// Inherit from this base event type to create custom event types
template<typename K>
struct Event
{
    using KeyType = const K;
};

/**
 * @class EventManager EventManager.h <fairmq/EventManager.h>
 * @brief Manages event callbacks from different subscribers
 *
 * The event manager stores a set of callbacks and associates them with
 * events depending on the callback signature. The first callback
 * argument must be of a special key type determined by the event type.
 *
 * Callbacks can be subscribed/unsubscribed based on a subscriber id,
 * the event type, and the callback signature.
 *
 * Events can be emitted based on event type and callback signature.
 *
 * The event manager is thread-safe.
 */
class EventManager
{
  public:
    template<typename E, typename ...Args>
    using Callback = std::function<void(typename E::KeyType, Args...)>;
    template<typename E, typename ...Args>
    using Signal = boost::signals2::signal<void(typename E::KeyType, Args...)>;

    template<typename E, typename ...Args>
    auto Subscribe(const std::string& subscriber, Callback<E, Args...> callback) -> void
    {
        const std::type_index event_type_index{typeid(E)};
        const std::type_index callback_type_index{typeid(Callback<E, Args...>)};
        const auto signalsKey = std::make_pair(event_type_index, callback_type_index);
        const auto connectionsKey = std::make_pair(subscriber, signalsKey);

        const auto connection = GetSignal<E, Args...>(signalsKey)->connect(callback);

        {
            std::lock_guard<std::mutex> lock{fMutex};

            if (fConnections.find(connectionsKey) != fConnections.end())
            {
                fConnections.at(connectionsKey).disconnect();
                fConnections.erase(connectionsKey);
            }
            fConnections.insert({connectionsKey, connection});
        }
    }

    template<typename E, typename ...Args>
    auto Unsubscribe(const std::string& subscriber) -> void
    {
        const std::type_index event_type_index{typeid(E)};
        const std::type_index callback_type_index{typeid(Callback<E, Args...>)};
        const auto signalsKey = std::make_pair(event_type_index, callback_type_index);
        const auto connectionsKey = std::make_pair(subscriber, signalsKey);

        std::lock_guard<std::mutex> lock{fMutex};

        fConnections.at(connectionsKey).disconnect();
        fConnections.erase(connectionsKey);
    }

    template<typename E, typename ...Args>
    auto Emit(typename E::KeyType& key, Args&&... args) const -> void
    {
        const std::type_index event_type_index{typeid(E)};
        const std::type_index callback_type_index{typeid(Callback<E, Args...>)};
        const auto signalsKey = std::make_pair(event_type_index, callback_type_index);

        (*GetSignal<E, Args...>(signalsKey))(key, std::forward<Args>(args)...);
    }

  private:
    using SignalsKey   = std::pair<std::type_index, std::type_index>;
                                // event          , callback
    using SignalsValue = boost::any;
    using SignalsMap   = std::unordered_map<SignalsKey, SignalsValue, boost::hash<SignalsKey>>;
    mutable SignalsMap fSignals;

    using ConnectionsKey   = std::pair<std::string, SignalsKey>;
                                    // subscriber , event/callback
    using ConnectionsValue = boost::signals2::connection;
    using ConnectionsMap   = std::unordered_map<ConnectionsKey, ConnectionsValue, boost::hash<ConnectionsKey>>;
    ConnectionsMap fConnections;

    mutable std::mutex fMutex;

    template<typename E, typename ...Args>
    auto GetSignal(const SignalsKey& key) const -> std::shared_ptr<Signal<E, Args...>>
    {
        std::lock_guard<std::mutex> lock{fMutex};

        if (fSignals.find(key) == fSignals.end())
        {
            // wrapper is needed because boost::signals2::signal is neither copyable nor movable
            // and I don't know how else to insert it into the map
            auto signal = std::make_shared<Signal<E, Args...>>();
            fSignals.insert(std::make_pair(key, signal));
        }

        return boost::any_cast<std::shared_ptr<Signal<E, Args...>>>(fSignals.at(key));
    }
}; /* class EventManager */

} /* namespace mq */
} /* namespace fair */

#endif /* FAIR_MQ_EVENTMANAGER_H */