rdf_list_iterator.hpp

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#ifndef RDF_LIST_ITERATOR_HPP_
#define RDF_LIST_ITERATOR_HPP_
#include "boost/iterator/iterator_facade.hpp"
#include "owlcpp/rdf/triple_store.hpp"
#include "owlcpp/rdf/exception.hpp"
#include "owlcpp/terms/node_tags_owl.hpp"
#include "owlcpp/rdf/print_node.hpp"

namespace owlcpp{

class Rdf_list_iter_s
: public boost::iterator_facade<
  Rdf_list_iter_s,
  Node_id const,
  boost::forward_traversal_tag
  >
{
public:
   struct Err : public Rdf_err {};

   Rdf_list_iter_s()
   : ts_(0), nid_(terms::rdf_nil::id())
   {}

   Rdf_list_iter_s(const Node_id nid, Triple_store const& ts)
   : ts_(&ts), nid_(nid)
   {}

private:
   Triple_store const* ts_;
   Node_id nid_;

   friend class boost::iterator_core_access;

   void increment() {
      const Triple_store::result_b<1,1,0,0>::type r = ts_->find_triple(
               nid_,
               terms::rdf_rest::id(),
               any(),
               any()
      );
      if( ! r ) BOOST_THROW_EXCEPTION(
               Err()
               << Err::msg_t("rdf:rest triple not found")
               << Err::str1_t(to_string(nid_, *ts_))
      );
      Triple const& t = r.front();
      if( boost::distance(r) != 1U ) BOOST_THROW_EXCEPTION(
               Err()
               << Err::msg_t("multiple rdf:rest triples")
               << Err::str1_t(to_string(nid_, *ts_))
      );
      nid_ = t.obj_;
   }

   Node_id const& dereference() const {
      const Triple_store::result_b<1,1,0,0>::type r = ts_->find_triple(
               nid_,
               terms::rdf_first::id(),
               any(),
               any()
      );
      if( ! r ) BOOST_THROW_EXCEPTION(
               Err()
               << Err::msg_t("rdf:first triple not found")
               << Err::str1_t(to_string(nid_, *ts_))
      );
      Triple const& t = r.front();
      if( boost::distance(r) != 1U ) BOOST_THROW_EXCEPTION(
               Err()
               << Err::msg_t("multiple rdf:first triples")
               << Err::str1_t(to_string(nid_, *ts_))
      );
      return t.obj_;
   }

   bool equal(Rdf_list_iter_s const& i) const {return nid_ == i.nid_;}
};

}//namespace owlcpp
#endif /* RDF_LIST_ITERATOR_HPP_ */