entity_range.hpp

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// ****************************************************************************
// entity/entity_iterator.h
//
// Iterates over a list of entities and a zipped component
// pool as a tuple.
// 
// Copyright Chris Glover 2014-2015
//
// Distributed under the Boost Software License, Version 1.0.
// See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt
//
// ****************************************************************************
#ifndef _ENTITY_ENTITYITERATOR_H_INCLUDED_
#define _ENTITY_ENTITYITERATOR_H_INCLUDED_

#include <boost/iterator/iterator_facade.hpp>

#include "entity/config.hpp" // IWYU pragma: keep
#include "entity/entity.hpp"
#include "entity/traits/iterator_traits.hpp"

namespace boost {
namespace iterators {
struct forward_traversal_tag;
}  // namespace iterators
}  // namespace boost

// ----------------------------------------------------------------------------
//
namespace entity
{
    // ------------------------------------------------------------------------
    //
    template<typename EntityListIterator, typename ZippedComponentWindows>
    class entity_incremental_iterator
        : public boost::iterator_facade<
            entity_incremental_iterator<EntityListIterator, ZippedComponentWindows>
        ,   ZippedComponentWindows
        ,   boost::forward_traversal_tag
        ,   ZippedComponentWindows
        >
    {
    public:

        entity_incremental_iterator(EntityListIterator begin, EntityListIterator end, ZippedComponentWindows windows)
            : entity_iter_(begin)
            , end_(end)
            , windows_(windows)
        {}

        entity get_entity() const
        {
            return *entity_iter_;
        }

    private:

        friend class boost::iterator_core_access;

        void increment()
        {
            ++entity_iter_;
            if(entity_iter_ != end_)
            {
                windows_.increment(*entity_iter_);
            }
        }

        bool equal(entity_incremental_iterator const& other) const
        {
            return entity_iter_ == other.entity_iter_;
        }

        ZippedComponentWindows dereference() const
        {
            return windows_;
        }

        EntityListIterator entity_iter_;
        EntityListIterator end_;
        ZippedComponentWindows windows_;

    };

    // ------------------------------------------------------------------------
    //
    template<typename EntityListIterator, typename ZippedComponentWindows>
    class entity_skipping_iterator
        : public boost::iterator_facade<
            entity_skipping_iterator<EntityListIterator, ZippedComponentWindows>
        ,   ZippedComponentWindows
        ,   boost::forward_traversal_tag
        ,   ZippedComponentWindows
        >
    {
    public:

        entity_skipping_iterator(EntityListIterator begin, EntityListIterator end, ZippedComponentWindows windows)
            : entity_iter_(begin)
            , end_(end)
            , windows_(windows)
        {
            if(entity_iter_ != end_)
            {
                windows_.advance(*entity_iter_);
            }
        }
        
        entity get_entity() const
        {
            return *entity_iter_;
        }

    private:

        friend class boost::iterator_core_access;

        void increment()
        {
            ++entity_iter_;
            if(entity_iter_ != end_)
            {
                windows_.advance(*entity_iter_);
            }
        }

        bool equal(entity_skipping_iterator const& other) const
        {
            return entity_iter_ == other.entity_iter_;
        }

        ZippedComponentWindows dereference() const
        {
            return windows_;
        }

        EntityListIterator entity_iter_;
        EntityListIterator end_;
        ZippedComponentWindows windows_;

    };

    // ------------------------------------------------------------------------
    //
    template<typename Iterator, typename EndIterator = Iterator>
    class entity_range
    {
    public:

        entity_range(Iterator begin, EndIterator end)
            : begin_(std::move(begin))
            , end_(std::move(end))
        {}

        Iterator begin()
        {
            return begin_;
        }

        EndIterator end()
        {
            return end_;
        }

    private:

        Iterator begin_;
        EndIterator end_;
    };

    template<typename Iterator, typename EndIterator>
    Iterator begin(entity_range<Iterator, EndIterator>& r)
    {
        return r.begin();
    }

    template<typename Iterator, typename EndIterator>
    EndIterator end(entity_range<Iterator, EndIterator>& r)
    {
        return r.end();
    }

    // ------------------------------------------------------------------------
    //
    template<typename EntityList, typename ZippedComponentWindows>
    auto make_entity_begin(iterator_traits::is_skipping_tag, EntityList const& entities, ZippedComponentWindows windows) -> entity_skipping_iterator<
        decltype(begin(entities)),
        ZippedComponentWindows>
    {
        return entity_skipping_iterator<
            decltype(begin(entities)),
            ZippedComponentWindows
        >(begin(entities), end(entities), std::move(windows));
    }

    template<typename EntityList, typename ZippedComponentWindows>
    auto make_entity_end(iterator_traits::is_skipping_tag, EntityList const& entities, ZippedComponentWindows windows) -> entity_skipping_iterator<
        decltype(end(entities)),
        ZippedComponentWindows>
    {
        return entity_skipping_iterator<
            decltype(begin(entities)),
            ZippedComponentWindows
        >(end(entities), end(entities), std::move(windows));
    }

    // --------------------------------------------------------------------
    //
    template<typename EntityList, typename ZippedComponentWindows>
    auto make_entity_begin(iterator_traits::is_incremental_tag, EntityList const& entities, ZippedComponentWindows windows) -> entity_incremental_iterator<
        decltype(entities.begin()),
        ZippedComponentWindows>
    {
        return entity_incremental_iterator<
            decltype(entities.begin()),
            ZippedComponentWindows
        >(entities.begin(), entities.end(), std::move(windows));
    }

    template<typename EntityList, typename ZippedComponentWindows>
    auto make_entity_end(iterator_traits::is_incremental_tag, EntityList& entities, ZippedComponentWindows windows) -> entity_incremental_iterator<
        decltype(entities.end()),
        ZippedComponentWindows>
    {
        return entity_incremental_iterator<
            decltype(entities.begin()),
            ZippedComponentWindows
        >(entities.end(), entities.end(), std::move(windows));
    }

    // --------------------------------------------------------------------
    //
    template<typename EntityList, typename ZippedComponentWindows>
    auto make_entity_begin(EntityList const& list, ZippedComponentWindows windows) -> decltype(make_entity_begin(iterator_traits::entity_list_is_incremental<EntityList>(), list, windows))
    {
        return make_entity_begin(
            iterator_traits::entity_list_is_incremental<EntityList>(),
            list, 
            std::move(windows)
        );
    }

    template<typename EntityList, typename ZippedComponentWindows>
    auto make_entity_end(EntityList const& list, ZippedComponentWindows windows) -> decltype(make_entity_end(iterator_traits::entity_list_is_incremental<EntityList>(), list, windows))
    {
        return make_entity_end(
            iterator_traits::entity_list_is_incremental<EntityList>(),
            list,
            std::move(windows)
        );
    }

    // --------------------------------------------------------------------
    //
    template<typename EntityList, typename ZippedComponentWindows>
    auto make_entity_range(EntityList const& list, ZippedComponentWindows windows) -> entity_range<decltype(make_entity_begin(list, windows)), decltype(make_entity_end(list, windows))>
    {
        return entity_range<
            decltype(make_entity_begin(list, windows)), 
            decltype(make_entity_end(list, windows))>(
                make_entity_begin(list, windows),
                make_entity_end(list, windows)
            )
        ;
    }
}

#endif // _ENTITY_ENTITYITERATOR_H_INCLUDED_