// -*- C++ -*-

#ifndef HUGO_DIJKSTRA_H

#define HUGO_DIJKSTRA_H

///\ingroup flowalgs

///\file

///\brief Dijkstra algorithm.

#include <hugo/bin_heap.h>

#include <hugo/invalid.h>

namespace hugo {

/// \addtogroup flowalgs

/// @{

  ///%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 GR The graph type the algorithm runs on.

  ///\param LM 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".

  ///

  ///\author Jacint Szabo and Alpar Juttner

  ///\todo We need a typedef-names should be standardized. (-:

  ///\todo Type of \c PredMap, \c PredNodeMap and \c DistMap

  ///should not be fixed. (Problematic to solve).

#ifdef DOXYGEN

  template <typename GR,

	    typename LM,

	    typename Heap>

#else

  template <typename GR,

	    typename LM=typename GR::template EdgeMap<int>,

	    template <class,class,class,class> class Heap = BinHeap >

#endif

  class Dijkstra{

  public:

    ///The type of the underlying graph.

    typedef GR Graph;

    ///.

    typedef typename Graph::Node Node;

    ///.

    typedef typename Graph::NodeIt NodeIt;

    ///.

    typedef typename Graph::Edge Edge;

    ///.

    typedef typename Graph::OutEdgeIt OutEdgeIt;

    ///The type of the length of the edges.

    typedef typename LM::ValueType ValueType;

    ///The type of the map that stores the edge lengths.

    typedef LM LengthMap;

    ///\brief The type of the map that stores the last

    ///edges of the shortest paths.

    typedef typename Graph::template NodeMap<Edge> PredMap;

    ///\brief The type of the map that stores the last but one

    ///nodes of the shortest paths.

    typedef typename Graph::template NodeMap<Node> PredNodeMap;

    ///The type of the map that stores the dists of the nodes.

    typedef typename Graph::template NodeMap<ValueType> DistMap;

  private:

    /// Pointer to the underlying graph.

    const Graph *G;

    /// Pointer to the length map

    const LM *length;

    ///Pointer to the map of predecessors edges.

    PredMap *predecessor;

    ///Indicates if \ref predecessor is locally allocated (\c true) or not.

    bool local_predecessor;

    ///Pointer to the map of predecessors nodes.

    PredNodeMap *pred_node;

    ///Indicates if \ref pred_node is locally allocated (\c true) or not.

    bool local_pred_node;

    ///Pointer to the map of distances.

    DistMap *distance;

    ///Indicates if \ref distance is locally allocated (\c true) or not.

    bool local_distance;

    ///The source node of the last execution.

    Node source;

    ///Initializes the maps.

    ///\todo Error if \c G or are \c NULL. What about \c length?

    ///\todo Better memory allocation (instead of new).

    void init_maps() 

    {

      if(!predecessor) {

	local_predecessor = true;

	predecessor = new PredMap(*G);

      }

      if(!pred_node) {

	local_pred_node = true;

	pred_node = new PredNodeMap(*G);

      }

      if(!distance) {

	local_distance = true;

	distance = new DistMap(*G);

      }

    }

  public :

    ///Constructor.

    ///\param _G the graph the algorithm will run on.

    ///\param _length the length map used by the algorithm.

    Dijkstra(const Graph& _G, const LM& _length) :

      G(&_G), length(&_length),

      predecessor(NULL), local_predecessor(false),

      pred_node(NULL), local_pred_node(false),

      distance(NULL), local_distance(false)

    { }

    ///Destructor.

    ~Dijkstra() 

    {

      if(local_predecessor) delete predecessor;

      if(local_pred_node) delete pred_node;

      if(local_distance) delete distance;

    }

    ///Sets the length map.

    ///Sets the length map.

    ///\return <tt> (*this) </tt>

    Dijkstra &setLengthMap(const LM &m) 

    {

      length = &m;

      return *this;

    }

    ///Sets the map storing the predecessor edges.

    ///Sets the map storing the predecessor edges.

    ///If you don't use this function before calling \ref run(),

    ///it will allocate one. The destuctor deallocates this

    ///automatically allocated map, of course.

    ///\return <tt> (*this) </tt>

    Dijkstra &setPredMap(PredMap &m) 

    {

      if(local_predecessor) {

	delete predecessor;

	local_predecessor=false;

      }

      predecessor = &m;

      return *this;

    }

    ///Sets the map storing the predecessor nodes.

    ///Sets the map storing the predecessor nodes.

    ///If you don't use this function before calling \ref run(),

    ///it will allocate one. The destuctor deallocates this

    ///automatically allocated map, of course.

    ///\return <tt> (*this) </tt>

    Dijkstra &setPredNodeMap(PredNodeMap &m) 

    {

      if(local_pred_node) {

	delete pred_node;

	local_pred_node=false;

      }

      pred_node = &m;

      return *this;

    }

    ///Sets the map storing the distances calculated by the algorithm.

    ///Sets the map storing the distances calculated by the algorithm.

    ///If you don't use this function before calling \ref run(),

    ///it will allocate one. The destuctor deallocates this

    ///automatically allocated map, of course.

    ///\return <tt> (*this) </tt>

    Dijkstra &setDistMap(DistMap &m) 

    {

      if(local_distance) {

	delete distance;

	local_distance=false;

      }

      distance = &m;

      return *this;

    }

  ///Runs %Dijkstra algorithm from node \c s.

  ///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.

    void run(Node s) {

      init_maps();

      source = s;

      for ( NodeIt u(*G) ; u!=INVALID ; ++u ) {

	predecessor->set(u,INVALID);

	pred_node->set(u,INVALID);

      }

      typename GR::template NodeMap<int> heap_map(*G,-1);

      typedef Heap<Node, ValueType, typename GR::template NodeMap<int>,

      std::less<ValueType> > 

      HeapType;

      HeapType heap(heap_map);

      heap.push(s,0); 

      while ( !heap.empty() ) {

	Node v=heap.top(); 

	ValueType oldvalue=heap[v];

	heap.pop();

	distance->set(v, oldvalue);

	for(OutEdgeIt e(*G,v); e!=INVALID; ++e) {

	  Node w=G->head(e); 

	  switch(heap.state(w)) {

	  case HeapType::PRE_HEAP:

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

	    predecessor->set(w,e);

	    pred_node->set(w,v);

	    break;

	  case HeapType::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 HeapType::POST_HEAP:

	    break;

	  }

	}

      }

    }

    ///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 of a shortest path from the root to \c

    ///v. It is \ref 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.

    ///\todo predEdge could be a better name.

    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.

    ///\note The root node is reported to be reached!

    ///\pre \ref run() must be called before using this function.

    ///

    bool reached(Node v) { return v==source || (*predecessor)[v]!=INVALID; }

  };

/// @}

} //END OF NAMESPACE HUGO

#endif