#define SKELETON

// -*- c++ -*- //

///\ingroup concept

///\file

///\brief Classes for representing paths in graphs.

#ifndef LEMON_PATH_H

#define LEMON_PATH_H

#include <lemon/invalid.h>

namespace lemon {

  namespace concept {

    /// \addtogroup concept

    /// @{

    //! \brief A skeleton structure for representing directed paths in a graph.

    //!

    //! A skeleton structure for representing directed paths in a graph.

    //! \param GR The graph type in which the path is.

    //! 

    //! In a sense, the path can be treated as a graph, for is has \c NodeIt

    //! and \c EdgeIt with the same usage. These types converts to the \c Node

    //! and \c Edge of the original graph.

    template<typename GR>

    class Path {

    public:

      /// Type of the underlying graph.

      typedef /*typename*/ GR Graph;

      /// Edge type of the underlying graph.

      typedef typename Graph::Edge GraphEdge; 

      /// Node type of the underlying graph.

     typedef typename Graph::Node GraphNode;

      class NodeIt;

      class EdgeIt;

      /// \param _G The graph in which the path is.

      ///

      Path(const Graph &_G) {}

      /// Length of the path.

      size_t length() const {}

      /// Returns whether the path is empty.

      bool empty() const {}

      /// Resets the path to an empty path.

      void clear() {}

      /// \brief Starting point of the path.

      ///

      /// Starting point of the path.

      /// Returns INVALID if the path is empty.

      GraphNode head() const {}

      /// \brief End point of the path.

      ///

      /// End point of the path.

      /// Returns INVALID if the path is empty.

      GraphNode tail() const {}

      /// \brief First NodeIt/EdgeIt.

      ///

      /// Initializes node or edge iterator to point to the first

      /// node or edge.

      template<typename It>

      It& first(It &i) const { return i=It(*this); }

      /// \brief The head of an edge.

      ///

      /// Returns node iterator pointing to the head node of the

      /// given edge iterator.

      NodeIt head(const EdgeIt& e) const {}

      /// \brief The tail of an edge.

      ///

      /// Returns node iterator pointing to the tail node of the

      /// given edge iterator.

      NodeIt tail(const EdgeIt& e) const {}

      /* Iterator classes */

      /**

       * \brief Iterator class to iterate on the edges of the paths

       * 

       * \ingroup concept

       * This class is used to iterate on the edges of the paths

       *

       * Of course it converts to Graph::Edge

       * 

       */

      class EdgeIt {

      public:

	/// Default constructor

	EdgeIt() {}

	/// Invalid constructor

	EdgeIt(Invalid) {}

	/// Constructor with starting point

	EdgeIt(const Path &_p) {}

	operator GraphEdge () const {}

	/// Next edge

	EdgeIt& operator++() {}

	/// Comparison operator

	bool operator==(const EdgeIt& e) const {}

	/// Comparison operator

	bool operator!=(const EdgeIt& e) const {}

// 	/// Comparison operator

//      /// \todo It is not clear what is the "natural" ordering.

// 	bool operator<(const EdgeIt& e) const {}

      };

      /**

       * \brief Iterator class to iterate on the nodes of the paths

       * 

       * \ingroup concept

       * This class is used to iterate on the nodes of the paths

       *

       * Of course it converts to Graph::Node.

       * 

       */

      class NodeIt {

      public:

	/// Default constructor

	NodeIt() {}

	/// Invalid constructor

	NodeIt(Invalid) {}

	/// Constructor with starting point

	NodeIt(const Path &_p) {}

	///Conversion to Graph::Node

	operator const GraphNode& () const {}

	/// Next node

	NodeIt& operator++() {}

	/// Comparison operator

	bool operator==(const NodeIt& e) const {}

	/// Comparison operator

	bool operator!=(const NodeIt& e) const {}

// 	/// Comparison operator

//      /// \todo It is not clear what is the "natural" ordering.

// 	bool operator<(const NodeIt& e) const {}

      };

      friend class Builder;    

      /**

       * \brief Class to build paths

       * 

       * \ingroup concept

       * This class is used to fill a path with edges.

       *

       * You can push new edges to the front and to the back of the path in

       * arbitrary order then you should commit these changes to the graph.

       *

       * While the builder is active (after the first modifying

       * operation and until the call of \ref commit())

       * the underlining Path is in a

       * "transitional" state (operations on it have undefined result).

       */

      class Builder {

      public:

        Path &P;

	///\param _P the path you want to fill in.

	///

	Builder(Path &_P) : P(_P) {}

	/// Sets the starting node of the path.

	/// Sets the starting node of the path. Edge added to the path

	/// afterwards have to be incident to this node.

	/// You \em must start building an empry path with this functions.

	/// (And you \em must \em not use it later).

	/// \sa pushFront()

	/// \sa pushBack()

	void setStartNode(const GraphNode &) {}

	///Push a new edge to the front of the path

	///Push a new edge to the front of the path.

	///If the path is empty, you \em must call \ref setStartNode() before

	///the first use of \ref pushFront().

	void pushFront(const GraphEdge& e) {}

	///Push a new edge to the back of the path

	///Push a new edge to the back of the path.

	///If the path is empty, you \em must call \ref setStartNode() before

	///the first use of \ref pushBack().

	void pushBack(const GraphEdge& e) {}

	///Commit the changes to the path.

	void commit() {}

	///Reserve (front) storage for the builder in advance.

	///If you know an reasonable upper bound of the number of the edges

	///to add to the front of the path,

	///using this function you may speed up the building.

	void reserveFront(size_t r) {}

	///Reserve (back) storage for the builder in advance.

	///If you know an reasonable upper bound of the number of the edges

	///to add to the back of the path,

	///using this function you may speed up the building.

	void reserveBack(size_t r) {}

      };

    };

  ///@}

  }

} // namespace lemon

#endif // LEMON_PATH_H