// See www.openfst.org for extensive documentation on this weighted
  // finite-state transducer library.
  //
  // Creates the union of two FSTs.
  
  #include <cstring>
  
  #include <memory>
  #include <string>
  
  #include <fst/flags.h>
  #include <fst/log.h>
  #include <fst/script/union.h>
  
  int fstunion_main(int argc, char **argv) {
    namespace s = fst::script;
    using fst::script::FstClass;
    using fst::script::MutableFstClass;
  
    string usage = "Creates the union of two FSTs.
  
    Usage: ";
    usage += argv[0];
    usage += " in1.fst in2.fst [out.fst]
  ";
  
    std::set_new_handler(FailedNewHandler);
    SET_FLAGS(usage.c_str(), &argc, &argv, true);
    if (argc < 3 || argc > 4) {
      ShowUsage();
      return 1;
    }
  
    const string in1_name = strcmp(argv[1], "-") != 0 ? argv[1] : "";
    const string in2_name = strcmp(argv[2], "-") != 0 ? argv[2] : "";
    const string out_name = argc > 3 ? argv[3] : "";
  
    if (in1_name == "" && in2_name == "") {
      LOG(ERROR) << argv[0] << ": Can't take both inputs from standard input";
      return 1;
    }
  
    std::unique_ptr<MutableFstClass> fst1(MutableFstClass::Read(in1_name, true));
    if (!fst1) return 1;
  
    std::unique_ptr<FstClass> fst2(FstClass::Read(in2_name));
    if (!fst2) return 1;
  
    s::Union(fst1.get(), *fst2);
  
    return !fst1->Write(out_name);
  }