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

 /**

  *

  * Class for representing paths in graphs.

  *

  */

 #ifndef HUGO_PATH_H

 #define HUGO_PATH_H

 #include <deque>

 #include <invalid.h>

 namespace hugo {

   /* Ennek az allocatorosdinak sokkal jobban utana kene nezni a hasznalata

      elott. Eleg bonyinak nez ki, ahogyan azokat az STL-ben hasznaljak. */

   template<typename Graph>

   class Path {

   public:

     typedef typename Graph::Edge GraphEdge;

     typedef typename Graph::Node GraphNode;

     class NodeIt;

     class EdgeIt;

   protected:

     Graph& G;

     // FIXME: ehelyett eleg lenne tarolni ket boolt: a ket szelso el

     // iranyitasat:

     GraphNode _first, _last;

     typedef std::deque<GraphEdge> Container;

     Container edges;

   public:

     Path(Graph &_G) : G(_G), _first(INVALID), _last(INVALID) {}

     /// Subpath defined by two nodes

     Path(Path const& P, NodeIt a, NodeIt b) { FIXME; }

     /// Subpath defined by tow edges. Contains edges in [a,b)

     Path(Path const& P, EdgeIt a, EdgeIt b) { FIXME; }

     size_t length() const { return edges.size(); }

     GraphNode from() const { return _first; }

     GraphNode to() const { return _last; }

     NodeIt& first(NodeIt &n) const { return nth(n, 0); }

     EdgeIt& first(EdgeIt &e) const { return nth(e, 0); }

     template<typename It>

     It first() const { 

       It e;

       first(e);

       return e; 

     }

     NodeIt& nth(NodeIt &, size_t) const;

     EdgeIt& nth(EdgeIt &, size_t) const;

     template<typename It>

     It nth(size_t n) const { 

       It e;

       nth(e, n);

       return e; 

     }

     bool valid(const NodeIt &n) const { return n.idx <= length(); }

     bool valid(const EdgeIt &e) const { return e.it < edges.end(); }

     bool isForward(const EdgeIt &e) const { return e.forw; }

     EdgeIt& next(EdgeIt &e) const;

     NodeIt& next(NodeIt &n) const;

     template <typename It>

     It getNext(It it) const {

       It tmp(it); return next(tmp);

     }

     // A path is constructed using the following four functions.

     // They return false if the requested operation is inconsistent

     // with the path constructed so far.

     // If your path has only one edge you MUST set either "from" or "to"!

     // So you probably SHOULD call it in any case to be safe (and check the

     // returned value to check if your path is consistent with your idea).

     bool pushFront(const GraphEdge &e);

     bool pushBack(const GraphEdge &e);

     bool setFrom(const GraphNode &n);

     bool setTo(const GraphNode &n);

     // WARNING: these two functions return the head/tail of an edge with

     // respect to the direction of the path!

     // So G.head(P.graphEdge(e)) == P.graphNode(P.head(e)) holds only if 

     // P.forward(e) is true (or the edge is a loop)!

     NodeIt head(const EdgeIt& e) const;

     NodeIt tail(const EdgeIt& e) const;

     // FIXME: ezeknek valami jobb nev kellene!!!

     GraphEdge graphEdge(const EdgeIt& e) const;

     GraphNode graphNode(const NodeIt& n) const;

     /*** Iterator classes ***/

     class EdgeIt {

       friend class Path;

       typename Container::const_iterator it;

       bool forw;

     public:

       // FIXME: jarna neki ilyen is...

       // EdgeIt(Invalid);

       bool forward() const { return forw; }

       bool operator==(const EdgeIt& e) const { return it==e.it; }

       bool operator!=(const EdgeIt& e) const { return it!=e.it; }

       bool operator<(const EdgeIt& e) const { return it<e.it; }

     };

     class NodeIt {

       friend class Path;

       friend class EdgeIt;

       int idx;

       bool tail;  // Is this node the tail of the edge with same idx?

     public:

       // FIXME: jarna neki ilyen is...

       // NodeIt(Invalid);

       bool operator==(const NodeIt& n) const { return idx==n.idx; }

       bool operator!=(const NodeIt& n) const { return idx!=n.idx; }

       bool operator<(const NodeIt& n) const { return idx<n.idx; }

     };

   private:

     bool edgeIncident(const GraphEdge &e, const GraphNode &a,

 		      GraphNode &b);

     bool connectTwoEdges(const GraphEdge &e, const GraphEdge &f);

   };

   template<typename Gr>

   typename Path<Gr>::EdgeIt&

   Path<Gr>::next(Path::EdgeIt &e) const {

     if( e.it == edges.end() ) 

       return e;

     GraphNode common_node = ( e.forw ? G.head(*e.it) : G.tail(*e.it) );

     ++e.it;

     // Invalid edgeit is always forward :)

     if( e.it == edges.end() ) {

       e.forw = true;

       return e;

     }

     e.forw = ( G.tail(*e.it) == common_node );

     return e;

   }

   template<typename Gr>

   typename Path<Gr>::NodeIt& Path<Gr>::next(NodeIt &n) const {

     if( n.idx >= length() ) {

       // FIXME: invalid

       n.idx = length()+1;

       return n;

     }

     GraphNode next_node = ( n.tail ? G.head(edges[n.idx]) :

 			      G.tail(edges[n.idx]) );

     ++n.idx;

     if( n.idx < length() ) {

       n.tail = ( next_node == G.tail(edges[n.idx]) );

     }

     else {

       n.tail = true;

     }

     return n;

   }

   template<typename Gr>

   bool Path<Gr>::edgeIncident(const GraphEdge &e, const GraphNode &a,

 			  GraphNode &b) {

     if( G.tail(e) == a ) {

       b=G.head(e);

       return true;

     }

     if( G.head(e) == a ) {

       b=G.tail(e);

       return true;

     }

     return false;

   }

   template<typename Gr>

   bool Path<Gr>::connectTwoEdges(const GraphEdge &e,

 			     const GraphEdge &f) {

     if( edgeIncident(f, G.tail(e), _last) ) {

       _first = G.head(e);

       return true;

     }

     if( edgeIncident(f, G.head(e), _last) ) {

       _first = G.tail(e);

       return true;

     }

     return false;

   }

   template<typename Gr>

   bool Path<Gr>::pushFront(const GraphEdge &e) {

     if( G.valid(_first) ) {

 	if( edgeIncident(e, _first, _first) ) {

 	  edges.push_front(e);

 	  return true;

 	}

 	else

 	  return false;

     }

     else if( length() < 1 || connectTwoEdges(e, edges[0]) ) {

       edges.push_front(e);

       return true;

     }

     else

       return false;

   }

   template<typename Gr>

   bool Path<Gr>::pushBack(const GraphEdge &e) {

     if( G.valid(_last) ) {

 	if( edgeIncident(e, _last, _last) ) {

 	  edges.push_back(e);

 	  return true;

 	}

 	else

 	  return false;

     }

     else if( length() < 1 || connectTwoEdges(edges[0], e) ) {

       edges.push_back(e);

       return true;

     }

     else

       return false;

   }

   template<typename Gr>

   bool Path<Gr>::setFrom(const GraphNode &n) {

     if( G.valid(_first) ) {

       return _first == n;

     }

     else {

       if( length() > 0) {

 	if( edgeIncident(edges[0], n, _last) ) {

 	  _first = n;

 	  return true;

 	}

 	else return false;

       }

       else {

 	_first = _last = n;

 	return true;

       }

     }

   }

   template<typename Gr>

   bool Path<Gr>::setTo(const GraphNode &n) {

     if( G.valid(_last) ) {

       return _last == n;

     }

     else {

       if( length() > 0) {

 	if( edgeIncident(edges[0], n, _first) ) {

 	  _last = n;

 	  return true;

 	}

 	else return false;

       }

       else {

 	_first = _last = n;

 	return true;

       }

     }

   }

   template<typename Gr>

   typename Path<Gr>::NodeIt

   Path<Gr>::tail(const EdgeIt& e) const {

     NodeIt n;

     if( e.it == edges.end() ) {

       // FIXME: invalid-> invalid

       n.idx = length() + 1;

       n.tail = true;

       return n;

     }

     n.idx = e.it-edges.begin();

     n.tail = e.forw;

   }

   template<typename Gr>

   typename Path<Gr>::NodeIt

   Path<Gr>::head(const EdgeIt& e) const {

     if( e.it == edges.end()-1 ) {

       return _last;

     }

     EdgeIt next_edge = e;

     next(next_edge);

     return tail(next_edge);

   }

   template<typename Gr>

   typename Path<Gr>::GraphEdge

   Path<Gr>::graphEdge(const EdgeIt& e) const {

     if( e.it != edges.end() ) {

       return *e.it;

     }

     else {

       return INVALID;

     }

   }

   template<typename Gr>

   typename Path<Gr>::GraphNode

   Path<Gr>::graphNode(const NodeIt& n) const {

     if( n.idx < length() ) {

       return n.tail ? G.tail(edges[n.idx]) : G.head(edges[n.idx]);

     }

     else if( n.idx == length() ) {

       return _last;

     }

     else {

       return INVALID;

     }

   }

   template<typename Gr>

   typename Path<Gr>::EdgeIt& Path<Gr>::nth(EdgeIt &e, size_t k) const {

     if( k<0 || k>=length() ) {

       // FIXME: invalid EdgeIt

       e.it = edges.end();

       e.forw = true;

       return e;

     }

     e.it = edges.begin()+k;

     if(k==0) {

       e.forw = ( G.tail(*e.it) == _first );

     }

     else {

       e.forw = ( G.tail(*e.it) == G.tail(edges[k-1]) ||

 		 G.tail(*e.it) == G.head(edges[k-1]) );

     }

     return e;

   }

   template<typename Gr>

   typename Path<Gr>::NodeIt& Path<Gr>::nth(NodeIt &n, size_t k) const {

     if( k<0 || k>length() ) {

       // FIXME: invalid NodeIt

       n.idx = length()+1;

       n.tail = true;

       return n;

     }

     if( k==length() ) {

       n.idx = length();

       n.tail = true;

       return n;

     }

     n = tail(nth<EdgeIt>(k));

     return n;

   }

 } // namespace hugo

 #endif // HUGO_PATH_H