// -*- 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