EventHypothesisLooper.h

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#ifndef DataFormats_EventHypothesis_interface_EventHypothesisLooper_h
#define DataFormats_EventHypothesis_interface_EventHypothesisLooper_h

#include "DataFormats/Candidate/interface/CandidateFwd.h"
#include <algorithm>

namespace pat { namespace eventhypothesis {
        template<typename T>
        class DynCastCandPtr {
            public:
                const T *get(const reco::Candidate *ptr) ;
                void clearCache() { isPtrCached_ = false; }
                bool typeOk(const reco::Candidate *ptr) { doPtr(ptr); return cachePtr_ != 0; }
            private:
                void       doPtr(const reco::Candidate *ptr) ;
                bool       isPtrCached_;
                const T *  cachePtr_;
        };
        template<typename T>
        void DynCastCandPtr<T>::doPtr(const reco::Candidate *ptr) {
            if (!isPtrCached_) { 
                cachePtr_    = dynamic_cast<const T *>(ptr); 
                isPtrCached_ = true;
            }
        }
        template<typename T>
        const T * DynCastCandPtr<T>::get(const reco::Candidate *ptr) {
            doPtr(ptr);
            if ((ptr != nullptr) && (cachePtr_ == 0)) throw cms::Exception("Type Checking") <<
                "You can't convert a " << typeid(*ptr).name() << " to a " << typeid(T).name() << "\n" <<
                "note: you can use c++filt command to convert the above in human readable types.\n";
            return cachePtr_;
        }

        template<>
        struct DynCastCandPtr<reco::Candidate> {
            const reco::Candidate *get(const reco::Candidate *ptr) { return ptr; }
            void clearCache() {}
            bool typeOk(const reco::Candidate *ptr) { return true; }
        };

        template<typename T>
        class Looper {
            public:
                Looper(const EventHypothesis &eh, const ParticleFilter &filter) ;

                Looper(const EventHypothesis &eh, const ParticleFilter *filter) ;
                Looper(const EventHypothesis &eh, const ParticleFilterPtr &filter) ;
                ~Looper() {}

                const T & operator*()  const { return ptr_.get(iter_->second.get()); }
                const T * operator->() const { return ptr_.get(iter_->second.get()); }
                const T * get()        const { return ptr_.get(iter_->second.get()); }
                
                bool  isTypeOk()       const { return ptr_.typeOk(iter_->second.get()); }

                const std::string &     role()  const { return  iter_->first; }
                const CandRefType &     ref ()  const { return  iter_->second; }
                const reco::Candidate & cand () const { return *iter_->second; }

                size_t globalIndex()  { return iter_ - eh_.begin(); }
                size_t index() const { return num_; }
                size_t size()  const { if (total_ < 0) realSize(); return total_; }

                Looper & operator++() ;                    
                Looper & operator--() ;                    
                Looper & skip(int delta) ; 
                Looper & reset(int item=0) ; 

                operator bool() const ;

                template<typename T2> bool operator==(const Looper<T2> &other) const { return iter_ == other.iter_; }
                template<typename T2> bool operator!=(const Looper<T2> &other) const { return iter_ != other.iter_; }
                template<typename T2> bool operator<=(const Looper<T2> &other) const { return iter_ <= other.iter_; }
                template<typename T2> bool operator>=(const Looper<T2> &other) const { return iter_ >= other.iter_; }
                template<typename T2> bool operator<(const Looper<T2> &other)  const { return iter_ < other.iter_; }
                template<typename T2> bool operator>(const Looper<T2> &other)  const { return iter_ > other.iter_; }

            private:
                struct null_deleter{  void operator()(void const *) const { } };
                typedef typename EventHypothesis::const_iterator const_iterator;

                void first() ;
                void realSize() const ; 
                bool assertOk() const;

                const EventHypothesis   & eh_;
                const ParticleFilterPtr   filter_;
                const_iterator            iter_;
                int                       num_;
                mutable int               total_; // mutable as it is not computed unless needed
                mutable DynCastCandPtr<T> ptr_;
        };
        typedef Looper<reco::Candidate> CandLooper;

        template<typename T>
        Looper<T>::Looper(const EventHypothesis &eh, const ParticleFilter &filter) :
            eh_(eh), filter_(ParticleFilterPtr(&filter, typename Looper<T>::null_deleter())), total_(-1)
        {
            first();
        }

        template<typename T>
        Looper<T>::Looper(const EventHypothesis &eh, const ParticleFilter *filter) :
            eh_(eh), filter_(filter), total_(-1)
        {
            first();
        }

       template<typename T>
        Looper<T>::Looper(const EventHypothesis &eh, const ParticleFilterPtr &filter) :
            eh_(eh), filter_(filter), total_(-1)
        {
            first();
        }


        template<typename T>
        bool Looper<T>::assertOk() const {
            assert(iter_ <= eh_.end());
            assert((iter_+1) >= eh_.begin());
            assert((iter_ < eh_.begin()) || (iter_ == eh_.end()) || ((*filter_)(*iter_)));
            return true;
        }

        template<typename T>
        Looper<T> & Looper<T>::operator++() { 
            ptr_.clearCache();
            assert(assertOk());
            if (iter_ == eh_.end()) return *this;
            do {
                ++iter_; 
                if (iter_ == eh_.end()) break;
                if ((*filter_)(*iter_)) {
                    assert(assertOk());
                    ++num_; return *this;
                }
            } while (true);
            assert(assertOk());
            return *this;
        }
        template<typename T>
        Looper<T> & Looper<T>::operator--() { 
            ptr_.clearCache();
            assert(assertOk());
            if (num_ < 0) return *this;
            do {
                --iter_; 
                if (iter_ < eh_.begin()) { num_ = -1; break; }
                if ((*filter_)(*iter_)) {
                    assert(assertOk());
                    --num_; return *this;
                }
            } while (true);
            assert(assertOk());
            return *this;
        }

        template<typename T>
        Looper<T> & Looper<T>::skip(int delta) {
            assert(assertOk());
            std::advance(this, delta);
            assert(assertOk());
            return *this;
        }
    
        template<typename T>
        Looper<T> & Looper<T>::reset(int item) {
            assert(assertOk());
            if (item >= 0) {
                first();
                std::advance(this, item);
            } else {
                num_ = item + 1; iter_ = eh_.end();
                std::advance(this, item);
            }
            assert(assertOk());
            return *this;
        }

        template<typename T>
        void Looper<T>::first() {
            num_ = 0; 
            iter_ = eh_.begin(); 
            ptr_.clearCache();
            for (; iter_ != eh_.end(); ++iter_) {
                if ((*filter_)(*iter_)) break;
            }
            assert(assertOk());
        }

        template<typename T>
        Looper<T>::operator bool() const {
            return  (iter_ < eh_.end()) && (iter_ >= eh_.begin());
        }

        template<typename T>
        void Looper<T>::realSize() const {
            EventHypothesis::const_iterator it = iter_;
            if (it < eh_.begin()) { 
                it = eh_.begin(); total_ = 0; 
            } else {
                total_ = num_;
            }
            for (; it != eh_.end(); ++it) { 
                if ((*filter_)(*it)) ++total_;
            }
        }
} } // namespaces

#endif