// -*- 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