// -*- 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