// See www.openfst.org for extensive documentation on this weighted
  // finite-state transducer library.
  //
  // Inverts a transduction.
  
  #include <cstring>
  
  #include <memory>
  #include <string>
  
  #include <fst/flags.h>
  #include <fst/script/invert.h>
  
  int fstinvert_main(int argc, char **argv) {
    namespace s = fst::script;
    using fst::script::MutableFstClass;
  
    string usage = "Inverts a transduction.
  
    Usage: ";
    usage += argv[0];
    usage += " [in.fst [out.fst]]
  ";
  
    std::set_new_handler(FailedNewHandler);
    SET_FLAGS(usage.c_str(), &argc, &argv, true);
    if (argc > 3) {
      ShowUsage();
      return 1;
    }
  
    const string in_name = (argc > 1 && strcmp(argv[1], "-") != 0) ? argv[1] : "";
    const string out_name = argc > 2 ? argv[2] : "";
  
    std::unique_ptr<MutableFstClass> fst(MutableFstClass::Read(in_name, true));
    if (!fst) return 1;
  
    s::Invert(fst.get());
  
    return !fst->Write(out_name);
  }