observer.hpp

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//This file is part of Bertini 2.
//
//bertini2/detail/observer.hpp is free software: you can redistribute it and/or modify
//it under the terms of the GNU General Public License as published by
//the Free Software Foundation, either version 3 of the License, or
//(at your option) any later version.
//
//bertini2/detail/observer.hpp is distributed in the hope that it will be useful,
//but WITHOUT ANY WARRANTY; without even the implied warranty of
//MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//GNU General Public License for more details.
//
//You should have received a copy of the GNU General Public License
//along with bertini2/detail/observer.hpp.  If not, see <http://www.gnu.org/licenses/>.
//
// Copyright(C) Bertini2 Development Team
//
// See <http://www.gnu.org/licenses/> for a copy of the license,
// as well as COPYING.  Bertini2 is provided with permitted
// additional terms in the b2/licenses/ directory.

 
#ifndef BERTINI_DETAIL_OBSERVER_HPP
#define BERTINI_DETAIL_OBSERVER_HPP
 
#include <tuple>
#include <typeindex>
#include <utility>
#include <vector>
 
#include <boost/fusion/adapted/std_tuple.hpp>
 
#include <boost/fusion/algorithm/iteration/for_each.hpp>
#include <boost/fusion/include/for_each.hpp>
 
#include "bertini2/detail/events.hpp"
 
namespace bertini{
 

    enum class ObserveResult { KeepObserving, Unsubscribe };
 

    class AnyObserver
    { BOOST_TYPE_INDEX_REGISTER_CLASS
    public:
        virtual ~AnyObserver() = default;

        virtual ObserveResult Observe(AnyEvent const& e) = 0;

        virtual std::vector<std::type_index> SubscribedEventTypes() const { return {}; }

        virtual std::type_index ObservedKind() const { return typeid(void); }
    };
 

    template<class ObservedT>
    class Observer : public AnyObserver
    { BOOST_TYPE_INDEX_REGISTER_CLASS
    public:
        virtual ~Observer() = default;
 
        std::type_index ObservedKind() const override { return typeid(ObservedT); }
    };
 
 
 

    template<class ObservedT, template<class> class... ObserverTypes>
    class MultiObserver : public Observer<ObservedT>
    {   BOOST_TYPE_INDEX_REGISTER_CLASS
    public:

        ObserveResult Observe(AnyEvent const& e) override
        {
            using namespace boost::fusion;
            bool keep = false;
            // Route through the AnyObserver interface: a glued-in observer may be a
            // TypedObserver, whose typed Observe(ConcreteEvent const&) overloads hide
            // the untyped Observe(AnyEvent const&) for ordinary name lookup.  The
            // virtual call reaches the right dispatcher in every case.
            auto f = [&e,&keep](auto &obs) {
                if (static_cast<AnyObserver&>(obs).Observe(e) == ObserveResult::KeepObserving)
                    keep = true;
            };
            for_each(observers_, f);
            return keep ? ObserveResult::KeepObserving : ObserveResult::Unsubscribe;
        }
 
        std::tuple<ObserverTypes<ObservedT>...> observers_;  
        virtual ~MultiObserver() = default;
    };
 

    template<class Derived, class ObservedT, class... ConcreteEvents>
    class TypedObserver : public Observer<ObservedT>
    { BOOST_TYPE_INDEX_REGISTER_CLASS
    public:
        std::vector<std::type_index> SubscribedEventTypes() const override
        {
            return { std::type_index(typeid(ConcreteEvents))... };
        }
 
        ObserveResult Observe(AnyEvent const& e) override
        {
            ObserveResult result = ObserveResult::KeepObserving;
            bool matched = false;
            // try each subscribed type; the first whose dynamic type matches wins.
            (TryDispatch<ConcreteEvents>(e, result, matched), ...);
            return result;
        }
 
        virtual ~TypedObserver() = default;
 
    private:
        template<class Ev>
        void TryDispatch(AnyEvent const& e, ObserveResult& result, bool& matched)
        {
            if (matched)
                return;
            if (auto p = dynamic_cast<const Ev*>(&e))
            {
                matched = true;
                result = static_cast<Derived*>(this)->OnEvent(*p);
            }
        }
    };
 
 
}
 
#endif