// -*- C++ -*-

#ifndef HUGO_BFS_H

#define HUGO_BFS_H

///\ingroup flowalgs

///\file

///\brief Bfs algorithm.

///

///\todo Revise Manual.

#include <hugo/bin_heap.h>

#include <hugo/invalid.h>

namespace hugo {

/// \addtogroup flowalgs

/// @{

  ///%BFS algorithm class.

  ///This class provides an efficient implementation of %BFS algorithm.

  ///\param GR The graph type the algorithm runs on.

  ///This class does the same as Dijkstra does with constant 1 edge length,

  ///but it is faster.

  ///

  ///\author Alpar Juttner

#ifdef DOXYGEN

  template <typename GR>

#else

  template <typename GR>

#endif

  class Bfs{

  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;

    ///\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<int> DistMap;

  private:

    const Graph *G;

    PredMap *predecessor;

    bool local_predecessor;

    PredNodeMap *pred_node;

    bool local_pred_node;

    DistMap *distance;

    bool local_distance;

    //The source node of the last execution.

    Node source;

    ///Initializes the maps.

    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 :    

    Bfs(const Graph& _G) :

      G(&_G),

      predecessor(NULL), local_predecessor(false),

      pred_node(NULL), local_pred_node(false),

      distance(NULL), local_distance(false)

    { }

    ~Bfs() 

    {

      if(local_predecessor) delete predecessor;

      if(local_pred_node) delete pred_node;

      if(local_distance) delete distance;

    }

    ///Sets the graph the algorithm will run on.

    ///Sets the graph the algorithm will run on.

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

    ///\bug What about maps?

    ///\todo It may be unnecessary

    Bfs &setGraph(const Graph &_G) 

    {

      G = &_G;

      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>

    Bfs &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>

    Bfs &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>

    Bfs &setDistMap(DistMap &m) 

    {

      if(local_distance) {

	delete distance;

	local_distance=false;

      }

      distance = &m;

      return *this;

    }

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

  ///This method runs the %BFS algorithm from a root node \c s

  ///in order to

  ///compute a

  ///shortest path to each node. The algorithm computes

  ///- The %BFS 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);

      }

      int N=G->nodeNum();

      std::vector<typename Graph::Node> Q(N);

      int Qh=0;

      int Qt=0;

      Q[Qh++]=source;

      distance->set(s, 0);

      do {

	Node m;

	Node n=Q[Qt++];

	int d= (*distance)[n]+1;

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

	  if((m=G->head(e))!=s && (*predecessor)[m]==INVALID) {

	    Q[Qh++]=m;

	    predecessor->set(m,e);

	    pred_node->set(m,n);

	    distance->set(m,d);

	  }

      } while(Qt!=Qh);

    }

    ///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.

    int dist(Node v) const { return (*distance)[v]; }

    ///Returns the 'previous edge' of the %BFS path tree.

    ///For a node \c v it returns the 'previous edge' of the %BFS 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

    ///%BFS tree used here is equal to the %BFS 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 %BFS tree.

    ///For a node \c v it returns the 'previous node' on the %BFS 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 %BFS

    ///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 %BFS tree map.

    ///Returns a reference to the NodeMap of the edges of the

    ///%BFS tree.

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

    const PredMap &predMap() const { return *predecessor;}

    ///Returns a reference to the map of last but one nodes of shortest paths.

    ///Returns a reference to the NodeMap of the last but one nodes on the

    ///%BFS 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 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