// -*- C++ -*-

 /* 

  *template <Graph, T, Heap=FibHeap, LengthMap=Graph::EdgeMap<T> >

  *

  *Constructor: 

  *

  *Dijkstra(Graph G, LengthMap length)

  *

  *

  *Methods:

  *

  *void run(Node s)

  *

  *T dist(Node v) : After run(s) was run, it returns the distance from s to v. 

  *   Returns T() if v is not reachable from s.

  *

  *Edge pred(Node v) : After run(s) was run, it returns the last 

  *   edge of a shortest s-v path. It is INVALID for s and for 

  *   the nodes not reachable from s.

  *

  *bool reached(Node v) : After run(s) was run, it is true iff v is 

  *   reachable from s

  *

  */

 #ifndef HUGO_DIJKSTRA_H

 #define HUGO_DIJKSTRA_H

 #include <fib_heap.h>

 #include <invalid.h>

 namespace hugo {

   //Alpar: Changed the order of the parameters

   ///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 posible 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.

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

   ///algorithm. The default

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

   template <typename Graph,

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

 	    typename Heap=BinHeap<typename Graph::Node,

 				  typename LengthMap::ValueType, 

 				  typename Graph::NodeMap<int> > >

   class Dijkstra{

   public:

     typedef typename LengthMap::ValueType ValueType;

     typedef typename Graph::NodeMap<Edge> PredMap;

     typedef typename Graph::NodeMap<Node> PredNodeMap;

     typedef typename Graph::NodeMap<ValueType> DistMap;

   private:

     typedef typename Graph::Node Node;

     typedef typename Graph::NodeIt NodeIt;

     typedef typename Graph::Edge Edge;

     typedef typename Graph::OutEdgeIt OutEdgeIt;

     const Graph& G;

     const LengthMap& length;

     PredMap predecessor;

     //In place of reach:

     PredNodeMap pred_node;

     DistMap distance;

     //I don't like this:

     //     //FIXME:

     //     typename Graph::NodeMap<bool> reach;

     //     //typename Graph::NodeMap<int> reach;

   public :

     /*

       The distance of the nodes is 0.

     */

     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 source.

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

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

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

     ///of this funcion is undefined.

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

     ///Returns the edges of the shortest path tree.

     ///For a node \c v it returns the last edge of the shortest path

     ///from \c s to \c v or INVALID if \c v is unreachable from \c s.

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

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

     ///Returns the nodes of the shortest paths.

     ///For a node \c v it returns the last but one node of the shortest path

     ///from \c s to \c v or INVALID if \c v is unreachable from \c s.

     ///\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.

     ///\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 paths.

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

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

     //    bool reached(Node v) { return reach[v]; }

     ///Chech if a node is reachable from \c s.

     ///Returns \c true if \c v is reachable from \c s.

     ///\warning \c s 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 \c s.

   ///This method runs the Dijkstra algorithm from 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.

   template <typename Graph, typename LengthMap, typename 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);

       // If a node is unreacheable, then why should be the dist=0?

       // distance.set(u,0);

       //      reach.set(u,false);

     }

     //We don't need it at all.

     //     //FIXME:

     //     typename Graph::NodeMap<bool> scanned(G,false);

     //     //typename Graph::NodeMap<int> scanned(G,false);

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

     Heap heap(heap_map);

     heap.push(s,0); 

     //    reach.set(s, true);

       while ( !heap.empty() ) {

 	Node v=heap.top(); 

 	ValueType oldvalue=heap[v];

 	heap.pop();

 	distance.set(v, oldvalue);

 	for(OutEdgeIt e(G,v); G.valid(e); G.next(e)) {

 	  Node w=G.head(e); 

 	  switch(heap.state(w)) {

 	  case Heap::PRE_HEAP:

 	    //	    reach.set(w,true);

 	    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;

 	  }

 	}

       }

   }

 } //END OF NAMESPACE HUGO

 #endif