// -*- 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 {

  template <typename Graph, typename T, 

    typename Heap=FibHeap<typename Graph::Node, T, 

    typename Graph::NodeMap<int> >, 

    typename LengthMap=typename Graph::EdgeMap<T> >

  class Dijkstra{

    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;

    typename Graph::NodeMap<Edge> predecessor;

    typename Graph::NodeMap<T> distance;

    typename Graph::NodeMap<bool> reach;

  public :

    /*

      The distance of the nodes is 0.

    */

    Dijkstra(Graph& _G, LengthMap& _length) : G(_G), 

      length(_length), predecessor(_G), distance(_G), reach(_G) { }

    void run(Node s) {

      NodeIt u;

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

	predecessor.set(u,INVALID);

	distance.set(u,0);

	reach.set(u,false);

      }

      typename Graph::NodeMap<bool> 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(); 

	T oldvalue=heap.get(v);

	heap.pop();

	distance.set(v, oldvalue);

	scanned.set(v,true);

	OutEdgeIt e;

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

	  Node w=G.head(e); 

	  if ( !scanned[w] ) {

	    if ( !reach[w] ) {

	      reach.set(w,true);

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

	      predecessor.set(w,e);

	    } else if ( oldvalue+length[e] < heap.get(w) ) {

	      predecessor.set(w,e);

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

	    }

	  }

	}

      }

    } 

    T dist(Node v) {

      return distance[v];

    }

    Edge pred(Node v) {

      return predecessor[v];

    }

    bool reached(Node v) {

      return reach[v];

    }

  };

}

#endif