// -*- c++ -*-

 #ifndef HUGO_EMPTYGRAPH_H

 #define HUGO_EMPTYGRAPH_H

 #include <invalid.h>

 /// The namespace of HugoLib

 namespace hugo {

   // @defgroup empty_graph The GraphSkeleton class

   // @{

   /// An empty graph class.

   /// This class provides all the common features of a grapf structure,

   /// however completely without implementations or real data structures

   /// behind the interface.

   /// All graph algorithms should compile with this class, but it will not

   /// run properly, of course.

   ///

   /// It can be used for checking the interface compatibility,

   /// or it can serve as a skeleton of a new graph structure.

   /// 

   /// Also, you will find here the full documentation of a certain graph

   /// feature, the documentation of a real graph imlementation

   /// like @ref ListGraph or

   /// @ref SmartGraph will just refer to this structure.

   class GraphSkeleton

   {

   public:

     /// The base type of the node iterators.

     /// This \c Node is the base type of each node iterators,

     /// thus each kind of node iterator will convert to this.

     class Node {

     public:

       /// @warning The default constructor sets the iterator

       /// to an undefined value.

       Node() {}   //FIXME

       /// Invalid constructor \& conversion.

       /// This constructor initializes the iterator to be invalid.

       /// \sa Invalid for more details.

       Node(Invalid) {}

       //Node(const Node &) {}

       /// Two iterators are equal if and only if they point to the

       /// same object or both are invalid.

       bool operator==(Node n) const { return true; }

       /// \sa \ref operator==(Node n)

       ///

       bool operator!=(Node n) const { return true; }

       bool operator<(Node n) const { return true; }

     };

     /// This iterator goes through each node.

     class NodeIt : public Node {

     public:

       /// @warning The default constructor sets the iterator

       /// to an undefined value.

       NodeIt() {} //FIXME

       /// Invalid constructor \& conversion.

       /// Initialize the iterator to be invalid

       /// \sa Invalid for more details.

       NodeIt(Invalid) {}

       /// Sets the iterator to the first node of \c G.

       NodeIt(const GraphSkeleton &G) {}

       /// @warning The default constructor sets the iterator

       /// to an undefined value.

       NodeIt(const NodeIt &) {}

     };

     /// The base type of the edge iterators.

     class Edge {

     public:

       /// @warning The default constructor sets the iterator

       /// to an undefined value.

       Edge() {}   //FIXME

       /// Initialize the iterator to be invalid

       Edge(Invalid) {}

       /// Two iterators are equal if and only if they point to the

       /// same object or both are invalid.

       bool operator==(Edge n) const { return true; }

       bool operator!=(Edge n) const { return true; }

       bool operator<(Edge n) const { return true; }

     };

     /// This iterator goes trought the outgoing edges of a certain graph.

     class OutEdgeIt : public Edge {

     public:

       /// @warning The default constructor sets the iterator

       /// to an undefined value.

       OutEdgeIt() {}

       /// Initialize the iterator to be invalid

       OutEdgeIt(Invalid) {}

       /// This constructor sets the iterator to first outgoing edge.

       /// This constructor set the iterator to the first outgoing edge of

       /// node

       ///@param n the node

       ///@param G the graph

       OutEdgeIt(const GraphSkeleton & G, Node n) {}

     };

     class InEdgeIt : public Edge {

     public:

       /// @warning The default constructor sets the iterator

       /// to an undefined value.

       InEdgeIt() {}

       /// Initialize the iterator to be invalid

       InEdgeIt(Invalid) {}

       InEdgeIt(const GraphSkeleton &, Node) {}    

     };

     //  class SymEdgeIt : public Edge {};

     class EdgeIt : public Edge {

     public:

       /// @warning The default constructor sets the iterator

       /// to an undefined value.

       EdgeIt() {}

       /// Initialize the iterator to be invalid

       EdgeIt(Invalid) {}

       EdgeIt(const GraphSkeleton &) {}

     };

     /// First node of the graph.

     /// \post \c i and the return value will be the first node.

     ///

     NodeIt &first(NodeIt &i) const { return i;}

     /// The first outgoing edge.

     InEdgeIt &first(InEdgeIt &i, Node n) const { return i;}

     /// The first incoming edge.

     OutEdgeIt &first(OutEdgeIt &i, Node n) const { return i;}

     //  SymEdgeIt &first(SymEdgeIt &, Node) const { return i;}

     /// The first edge of the Graph.

     EdgeIt &first(EdgeIt &i) const { return i;}

 //     Node getNext(Node) const {}

 //     InEdgeIt getNext(InEdgeIt) const {}

 //     OutEdgeIt getNext(OutEdgeIt) const {}

 //     //SymEdgeIt getNext(SymEdgeIt) const {}

 //     EdgeIt getNext(EdgeIt) const {}

     /// Go to the next node.

     NodeIt &next(NodeIt &i) const { return i;}

     /// Go to the next incoming edge.

     InEdgeIt &next(InEdgeIt &i) const { return i;}

     /// Go to the next outgoing edge.

     OutEdgeIt &next(OutEdgeIt &i) const { return i;}

     //SymEdgeIt &next(SymEdgeIt &) const {}

     /// Go to the next edge.

     EdgeIt &next(EdgeIt &i) const { return i;}

     ///Gives back the head node of an edge.

     Node head(Edge) const { return INVALID; }

     ///Gives back the tail node of an edge.

     Node tail(Edge) const { return INVALID; }

     //   Node aNode(InEdgeIt) const {}

     //   Node aNode(OutEdgeIt) const {}

     //   Node aNode(SymEdgeIt) const {}

     //   Node bNode(InEdgeIt) const {}

     //   Node bNode(OutEdgeIt) const {}

     //   Node bNode(SymEdgeIt) const {}

     /// Checks if a node iterator is valid

     bool valid(const Node) const { return true;}

     /// Checks if an edge iterator is valid

     bool valid(const Edge) const { return true;}

     ///Gives back the \e id of a node.

     ///\warning Not all graph structure provide this feature.

     ///

     int id(const Node) const { return 0;}

     ///Gives back the \e id of an edge.

     ///\warning Not all graph structure provide this feature.

     ///

     int id(const Edge) const { return 0;}

     //void setInvalid(Node &) const {};

     //void setInvalid(Edge &) const {};

     ///Add a new node to the graph.

     /// \return the new node.

     Node addNode() { return INVALID;}

     ///Add a new edge to the graph.

     ///Add a new edge to the graph with tail node \c tail

     ///and head node \c head.

     ///\return the new edge.

     Edge addEdge(Node tail, Node head) { return INVALID;}

     /// Deletes a node.

     ///\warning Not all graph structure provide this feature.

     ///

     void erase(Node n) {}

     /// Deletes an edge.

     ///\warning Not all graph structure provide this feature.

     ///

     void erase(Edge e) {}

     /// Reset the graph.

     /// This function deletes all edges and nodes of the graph.

     /// It also frees the memory allocated to store them.

     void clear() {}

     int nodeNum() const { return 0;}

     int edgeNum() const { return 0;}

     GraphSkeleton() {}

     GraphSkeleton(const GraphSkeleton &G) {}

     ///Read/write map of the nodes to type \c T.

     /// \todo We may need copy constructor

     /// \todo We may need conversion from other nodetype

     /// \todo We may need operator=

     template<class T> class NodeMap

     {

     public:

       typedef T ValueType;

       typedef Node KeyType;

       NodeMap(const GraphSkeleton &G) {}

       NodeMap(const GraphSkeleton &G, T t) {}

       template<typename TT> NodeMap(const NodeMap<TT> &m) {}

       /// Sets the value of a node.

       /// Sets the value associated with node \c i to the value \c t.

       ///

       void set(Node i, T t) {}

       /// Gets the value of a node.

       T get(Node i) const {return *(T*)0;}  //FIXME: Is it necessary

       T &operator[](Node i) {return *(T*)0;}

       const T &operator[](Node i) const {return *(T*)0;}

       /// Updates the map if the graph has been changed

       /// \todo Do we need this?

       ///

       void update() {}

       void update(T a) {}   //FIXME: Is it necessary

     };

     ///Read/write map of the edges to type \c T.

     ///Read/write map of the edges to type \c T.

     ///It behaves exactly the same way as \ref NodeMap.

     template<class T> class EdgeMap

     {

     public:

       typedef T ValueType;

       typedef Edge KeyType;

       EdgeMap(const GraphSkeleton &G) {}

       EdgeMap(const GraphSkeleton &G, T t) {}

       void set(Edge i, T t) {}

       T get(Edge i) const {return *(T*)0;}

       T &operator[](Edge i) {return *(T*)0;}

       void update() {}

       void update(T a) {}   //FIXME: Is it necessary

     };

   };

   // @}

 } //namespace hugo

 // class EmptyBipGraph : public Graph Skeleton

 // {

 //   class ANode {};

 //   class BNode {};

 //   ANode &next(ANode &) {}

 //   BNode &next(BNode &) {}

 //   ANode &getFirst(ANode &) const {}

 //   BNode &getFirst(BNode &) const {}

 //   enum NodeClass { A = 0, B = 1 };

 //   NodeClass getClass(Node n) {}

 // }

 #endif // HUGO_EMPTYGRAPH_H