// -*- C++ -*-

 #ifndef HUGO_DIJKSTRA_H

 #define HUGO_DIJKSTRA_H

 ///\file

 ///\brief Dijkstra algorithm.

 #include <bin_heap.h>

 #include <invalid.h>

 namespace hugo {

   ///%Dijkstra algorithm class.

   ///This class provides an efficient implementation of %Dijkstra algorithm.

   ///The edge lengths are passed to the algorithm using a

   ///\ref ReadMapSkeleton "readable map",

   ///so it is easy to change it to any kind of length.

   ///

   ///The type of the length is determined by the \c ValueType of the length map.

   ///

   ///It is also possible to change the underlying priority heap.

   ///

   ///\param Graph The graph type the algorithm runs on.

   ///\param LengthMap This read-only

   ///EdgeMap

   ///determines the

   ///lengths of the edges. It is read once for each edge, so the map

   ///may involve in relatively time consuming process to compute the edge

   ///length if it is necessary. The default map type is

   ///\ref GraphSkeleton::EdgeMap "Graph::EdgeMap<int>"

   ///\param Heap The heap type used by the %Dijkstra

   ///algorithm. The default

   ///is using \ref BinHeap "binary heap".

 #ifdef DOXYGEN

   template <typename Graph,

 	    typename LengthMap,

 	    typename Heap>

 #else

   template <typename Graph,

 	    typename LengthMap=typename Graph::EdgeMap<int>,

 	    template <class,class,class> class Heap = BinHeap >

 #endif

   class Dijkstra{

   public:

     typedef typename Graph::Node Node;

     typedef typename Graph::NodeIt NodeIt;

     typedef typename Graph::Edge Edge;

     typedef typename Graph::OutEdgeIt OutEdgeIt;

     typedef typename LengthMap::ValueType ValueType;

     typedef typename Graph::NodeMap<Edge> PredMap;

     typedef typename Graph::NodeMap<Node> PredNodeMap;

     typedef typename Graph::NodeMap<ValueType> DistMap;

   private:

     const Graph& G;

     const LengthMap& length;

     PredMap predecessor;

     PredNodeMap pred_node;

     DistMap distance;

   public :

     Dijkstra(Graph& _G, LengthMap& _length) :

       G(_G), length(_length), predecessor(_G), pred_node(_G), distance(_G) { }

     void run(Node s);

     ///The distance of a node from the root.

     ///Returns the distance of a node from the root.

     ///\pre \ref run() must be called before using this function.

     ///\warning If node \c v in unreachable from the root the return value

     ///of this funcion is undefined.

     ValueType dist(Node v) const { return distance[v]; }

     ///Returns the previous edge of the shortest path tree.

     ///For a node \c v it returns the previous edge of the shortest path tree,

     ///i.e. it returns the last edge from a shortest path from the root to \c

     ///v. It is INVALID if \c v is unreachable from the root or if \c v=s. The

     ///shortest path tree used here is equal to the shortest path tree used in

     ///\ref predNode(Node v).  \pre \ref run() must be called before using

     ///this function.

     Edge pred(Node v) const { return predecessor[v]; }

     ///Returns the previous node of the shortest path tree.

     ///For a node \c v it returns the previous node of the shortest path tree,

     ///i.e. it returns the last but one node from a shortest path from the

     ///root to \c /v. It is INVALID if \c v is unreachable from the root or if

     ///\c v=s. The shortest path tree used here is equal to the shortest path

     ///tree used in \ref pred(Node v).  \pre \ref run() must be called before

     ///using this function.

     Node predNode(Node v) const { return pred_node[v]; }

     ///Returns a reference to the NodeMap of distances.

     ///Returns a reference to the NodeMap of distances. \pre \ref run() must

     ///be called before using this function.

     const DistMap &distMap() const { return distance;}

     ///Returns a reference to the shortest path tree map.

     ///Returns a reference to the NodeMap of the edges of the

     ///shortest path tree.

     ///\pre \ref run() must be called before using this function.

     const PredMap &predMap() const { return predecessor;}

     ///Returns a reference to the map of nodes of shortest paths.

     ///Returns a reference to the NodeMap of the last but one nodes of the

     ///shortest path tree.

     ///\pre \ref run() must be called before using this function.

     const PredNodeMap &predNodeMap() const { return pred_node;}

     ///Checks if a node is reachable from the root.

     ///Returns \c true if \c v is reachable from the root.

     ///\warning the root node is reported to be unreached!

     ///\todo Is this what we want?

     ///\pre \ref run() must be called before using this function.

     ///

     bool reached(Node v) { return G.valid(predecessor[v]); }

   };

   // **********************************************************************

   //  IMPLEMENTATIONS

   // **********************************************************************

   ///Runs %Dijkstra algorithm from node the root.

   ///This method runs the %Dijkstra algorithm from a root node \c s

   ///in order to

   ///compute the

   ///shortest path to each node. The algorithm computes

   ///- The shortest path tree.

   ///- The distance of each node from the root.

   template <typename Graph, typename LengthMap,

 	    template<class,class,class> class Heap >

   void Dijkstra<Graph,LengthMap,Heap>::run(Node s) {

     NodeIt u;

     for ( G.first(u) ; G.valid(u) ; G.next(u) ) {

       predecessor.set(u,INVALID);

       pred_node.set(u,INVALID);

     }

     typename Graph::NodeMap<int> heap_map(G,-1);

     Heap<Node,ValueType,typename Graph::NodeMap<int> > heap(heap_map);

     heap.push(s,0); 

       while ( !heap.empty() ) {

 	Node v=heap.top(); 

 	ValueType oldvalue=heap[v];

 	heap.pop();

 	distance.set(v, oldvalue);

 	{ //FIXME this bracket is for e to be local

 	  OutEdgeIt e;

 	for(G.first(e, v);

 	    G.valid(e); G.next(e)) {

 	  Node w=G.head(e); 

 	  switch(heap.state(w)) {

 	  case heap.PRE_HEAP:

 	    heap.push(w,oldvalue+length[e]); 

 	    predecessor.set(w,e);

 	    pred_node.set(w,v);

 	    break;

 	  case heap.IN_HEAP:

 	    if ( oldvalue+length[e] < heap[w] ) {

 	      heap.decrease(w, oldvalue+length[e]); 

 	      predecessor.set(w,e);

 	      pred_node.set(w,v);

 	    }

 	    break;

 	  case heap.POST_HEAP:

 	    break;

 	  }

 	}

       } //FIXME tis bracket

       }

   }

 } //END OF NAMESPACE HUGO

 #endif