// -*- 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