text: // See www.openfst.org for extensive documentation on this weighted
  // finite-state transducer library.
  //
  // Generic FST augmented with state count-interface class definition.
  
  #ifndef FST_EXPANDED_FST_H_
  #define FST_EXPANDED_FST_H_
  
  #include <sys/types.h>
  
  #include <istream>
  #include <memory>
  #include <string>
  #include <vector>
  
  #include <fst/log.h>
  #include <fstream>
  
  #include <fst/fst.h>
  
  
  namespace fst {
  
  // A generic FST plus state count.
  template <class A>
  class ExpandedFst : public Fst<A> {
   public:
    using Arc = A;
    using StateId = typename Arc::StateId;
  
    virtual StateId NumStates() const = 0;  // State count
  
    // Get a copy of this ExpandedFst. See Fst<>::Copy() for further doc.
    ExpandedFst *Copy(bool safe = false) const override = 0;
  
    // Read an ExpandedFst from an input stream; return NULL on error.
    static ExpandedFst *Read(std::istream &strm, const FstReadOptions &opts) {
      FstReadOptions ropts(opts);
      FstHeader hdr;
      if (ropts.header) {
        hdr = *opts.header;
      } else {
        if (!hdr.Read(strm, opts.source)) return nullptr;
        ropts.header = &hdr;
      }
      if (!(hdr.Properties() & kExpanded)) {
        LOG(ERROR) << "ExpandedFst::Read: Not an ExpandedFst: " << ropts.source;
        return nullptr;
      }
      const auto reader =
          FstRegister<Arc>::GetRegister()->GetReader(hdr.FstType());
      if (!reader) {
        LOG(ERROR) << "ExpandedFst::Read: Unknown FST type \"" << hdr.FstType()
                   << "\" (arc type = \"" << A::Type() << "\"): " << ropts.source;
        return nullptr;
      }
      auto *fst = reader(strm, ropts);
      if (!fst) return nullptr;
      return static_cast<ExpandedFst *>(fst);
    }
  
    // Read an ExpandedFst from a file; return NULL on error.
    // Empty source reads from standard input.
    static ExpandedFst *Read(const std::string &source) {
      if (!source.empty()) {
        std::ifstream strm(source,
                                std::ios_base::in | std::ios_base::binary);
        if (!strm) {
          LOG(ERROR) << "ExpandedFst::Read: Can't open file: " << source;
          return nullptr;
        }
        return Read(strm, FstReadOptions(source));
      } else {
        return Read(std::cin, FstReadOptions("standard input"));
      }
    }
  };
  
  namespace internal {
  
  //  ExpandedFst<A> case - abstract methods.
  template <class Arc>
  inline typename Arc::Weight Final(const ExpandedFst<Arc> &fst,
                                    typename Arc::StateId s) {
    return fst.Final(s);
  }
  
  template <class Arc>
  inline ssize_t NumArcs(const ExpandedFst<Arc> &fst, typename Arc::StateId s) {
    return fst.NumArcs(s);
  }
  
  template <class Arc>
  inline ssize_t NumInputEpsilons(const ExpandedFst<Arc> &fst,
                                  typename Arc::StateId s) {
    return fst.NumInputEpsilons(s);
  }
  
  template <class Arc>
  inline ssize_t NumOutputEpsilons(const ExpandedFst<Arc> &fst,
                                   typename Arc::StateId s) {
    return fst.NumOutputEpsilons(s);
  }
  
  }  // namespace internal
  
  // A useful alias when using StdArc.
  using StdExpandedFst = ExpandedFst<StdArc>;
  
  // This is a helper class template useful for attaching an ExpandedFst
  // interface to its implementation, handling reference counting. It
  // delegates to ImplToFst the handling of the Fst interface methods.
  template <class Impl, class FST = ExpandedFst<typename Impl::Arc>>
  class ImplToExpandedFst : public ImplToFst<Impl, FST> {
   public:
    using Arc = typename FST::Arc;
    using StateId = typename Arc::StateId;
    using Weight = typename Arc::Weight;
  
    StateId NumStates() const override { return GetImpl()->NumStates(); }
  
   protected:
    using ImplToFst<Impl, FST>::GetImpl;
  
    explicit ImplToExpandedFst(std::shared_ptr<Impl> impl)
        : ImplToFst<Impl, FST>(impl) {}
  
    ImplToExpandedFst(const ImplToExpandedFst &fst, bool safe)
        : ImplToFst<Impl, FST>(fst, safe) {}
  
    static Impl *Read(std::istream &strm, const FstReadOptions &opts) {
      return Impl::Read(strm, opts);
    }
  
    // Read FST implementation from a file; return NULL on error.
    // Empty source reads from standard input.
    static Impl *Read(const std::string &source) {
      if (!source.empty()) {
        std::ifstream strm(source,
                                std::ios_base::in | std::ios_base::binary);
        if (!strm) {
          LOG(ERROR) << "ExpandedFst::Read: Can't open file: " << source;
          return nullptr;
        }
        return Impl::Read(strm, FstReadOptions(source));
      } else {
        return Impl::Read(std::cin, FstReadOptions("standard input"));
      }
    }
  };
  
  // Function to return the number of states in an FST, counting them
  // if necessary.
  template <class Arc>
  typename Arc::StateId CountStates(const Fst<Arc> &fst) {
    if (fst.Properties(kExpanded, false)) {
      const auto *efst = static_cast<const ExpandedFst<Arc> *>(&fst);
      return efst->NumStates();
    } else {
      typename Arc::StateId nstates = 0;
      for (StateIterator<Fst<Arc>> siter(fst); !siter.Done(); siter.Next()) {
        ++nstates;
      }
      return nstates;
    }
  }
  
  // Function to return the number of states in a vector of FSTs, counting them if
  // necessary.
  template <class Arc>
  typename Arc::StateId CountStates(const std::vector<const Fst<Arc> *> &fsts) {
    typename Arc::StateId nstates = 0;
    for (const auto *fst : fsts) nstates += CountStates(*fst);
    return nstates;
  }
  
  // Function to return the number of arcs in an FST.
  template <class F>
  size_t CountArcs(const F &fst) {
    size_t narcs = 0;
    for (StateIterator<F> siter(fst); !siter.Done(); siter.Next()) {
      narcs += fst.NumArcs(siter.Value());
    }
    return narcs;
  }
  
  }  // namespace fst
  
  #endif  // FST_EXPANDED_FST_H_
  