// See www.openfst.org for extensive documentation on this weighted
  // finite-state transducer library.
  
  #ifndef FST_SCRIPT_STATEITERATOR_CLASS_H_
  #define FST_SCRIPT_STATEITERATOR_CLASS_H_
  
  #include <memory>
  
  #include <fst/fstlib.h>
  #include <fst/script/fst-class.h>
  
  // Scripting API support for StateIterator.
  
  namespace fst {
  namespace script {
  
  // Virtual interface implemented by each concrete StateIteratorImpl<F>.
  class StateIteratorImplBase {
   public:
    virtual bool Done() const = 0;
    virtual int64 Value() const = 0;
    virtual void Next() = 0;
    virtual void Reset() = 0;
    virtual ~StateIteratorImplBase() {}
  };
  
  // Templated implementation.
  template <class Arc>
  class StateIteratorClassImpl : public StateIteratorImplBase {
   public:
    explicit StateIteratorClassImpl(const Fst<Arc> &fst) : siter_(fst) {}
  
    bool Done() const final { return siter_.Done(); }
  
    int64 Value() const final { return siter_.Value(); }
  
    void Next() final { siter_.Next(); }
  
    void Reset() final { siter_.Reset(); }
  
    ~StateIteratorClassImpl() override {}
  
   private:
    StateIterator<Fst<Arc>> siter_;
  };
  
  class StateIteratorClass;
  
  using InitStateIteratorClassArgs =
      std::pair<const FstClass &, StateIteratorClass *>;
  
  // Untemplated user-facing class holding a templated pimpl.
  class StateIteratorClass {
   public:
    explicit StateIteratorClass(const FstClass &fst);
  
    template <class Arc>
    explicit StateIteratorClass(const Fst<Arc> &fst)
        : impl_(new StateIteratorClassImpl<Arc>(fst)) {}
  
    bool Done() const { return impl_->Done(); }
  
    int64 Value() const { return impl_->Value(); }
  
    void Next() { impl_->Next(); }
  
    void Reset() { impl_->Reset(); }
  
    template <class Arc>
    friend void InitStateIteratorClass(InitStateIteratorClassArgs *args);
  
   private:
    std::unique_ptr<StateIteratorImplBase> impl_;
  };
  
  template <class Arc>
  void InitStateIteratorClass(InitStateIteratorClassArgs *args) {
    const Fst<Arc> &fst = *(std::get<0>(*args).GetFst<Arc>());
    std::get<1>(*args)->impl_.reset(new StateIteratorClassImpl<Arc>(fst));
  }
  
  }  // namespace script
  }  // namespace fst
  
  #endif  // FST_SCRIPT_STATEITERATOR_CLASS_H_