// -*- c++ -*- //

/**

 *

 * Class for representing paths in graphs.

 *

 */

#ifndef HUGO_PATH_H

#define HUGO_PATH_H

#include <deque>

#include <algorithm>

#include <invalid.h>

namespace hugo {

  /* Ennek az allocatorosdinak sokkal jobban utana kene nezni a hasznalata

     elott. Eleg bonyinak nez ki, ahogyan azokat az STL-ben hasznaljak. */

  template<typename Graph>

  class Path {

  public:

    typedef typename Graph::Edge GraphEdge;

    typedef typename Graph::Node GraphNode;

    class NodeIt;

    class EdgeIt;

  protected:

    Graph& G;

    // FIXME: ehelyett eleg lenne tarolni ket boolt: a ket szelso el

    // iranyitasat:

    GraphNode _first, _last;

    typedef std::deque<GraphEdge> Container;

    Container edges;

  public:

    Path(Graph &_G) : G(_G), _first(INVALID), _last(INVALID) {}

    /// Subpath defined by two nodes.

    /// Nodes may be in reversed order, then

    /// we contstruct the reversed path.

    Path(const Path &P, const NodeIt &a, const NodeIt &b);

    /// Subpath defined by two edges. Contains edges in [a,b)

    /// It is an error if the two edges are not in order!

    Path(const Path &P, const EdgeIt &a, const EdgeIt &b);

    size_t length() const { return edges.size(); }

    GraphNode from() const { return _first; }

    GraphNode to() const { return _last; }

    NodeIt& first(NodeIt &n) const { return nth(n, 0); }

    EdgeIt& first(EdgeIt &e) const { return nth(e, 0); }

    template<typename It>

    It first() const { 

      It e;

      first(e);

      return e; 

    }

    NodeIt& nth(NodeIt &, size_t) const;

    EdgeIt& nth(EdgeIt &, size_t) const;

    template<typename It>

    It nth(size_t n) const { 

      It e;

      nth(e, n);

      return e; 

    }

    bool valid(const NodeIt &n) const { return n.idx <= length(); }

    bool valid(const EdgeIt &e) const { return e.it < edges.end(); }

    bool isForward(const EdgeIt &e) const { return e.forw; }

    /// index of a node on the path. Returns length+2 for the invalid NodeIt

    int index(const NodeIt &n) const { return n.idx; }

    /// index of an edge on the path. Returns length+1 for the invalid EdgeIt

    int index(const EdgeIt &e) const { return e.it - edges.begin(); }

    EdgeIt& next(EdgeIt &e) const;

    NodeIt& next(NodeIt &n) const;

    template <typename It>

    It getNext(It it) const {

      It tmp(it); return next(tmp);

    }

    // A path is constructed using the following four functions.

    // They return false if the requested operation is inconsistent

    // with the path constructed so far.

    // If your path has only one edge you MUST set either "from" or "to"!

    // So you probably SHOULD call it in any case to be safe (and check the

    // returned value to check if your path is consistent with your idea).

    bool pushFront(const GraphEdge &e);

    bool pushBack(const GraphEdge &e);

    bool setFrom(const GraphNode &n);

    bool setTo(const GraphNode &n);

    // WARNING: these two functions return the head/tail of an edge with

    // respect to the direction of the path!

    // So G.head(P.graphEdge(e)) == P.graphNode(P.head(e)) holds only if 

    // P.forward(e) is true (or the edge is a loop)!

    NodeIt head(const EdgeIt& e) const;

    NodeIt tail(const EdgeIt& e) const;

    // FIXME: ezeknek valami jobb nev kellene!!!

    GraphEdge graphEdge(const EdgeIt& e) const;

    GraphNode graphNode(const NodeIt& n) const;

    /*** Iterator classes ***/

    class EdgeIt {

      friend class Path;

      typename Container::const_iterator it;

      bool forw;

    public:

      // FIXME: jarna neki ilyen is...

      // EdgeIt(Invalid);

      bool forward() const { return forw; }

      bool operator==(const EdgeIt& e) const { return it==e.it; }

      bool operator!=(const EdgeIt& e) const { return it!=e.it; }

      bool operator<(const EdgeIt& e) const { return it<e.it; }

    };

    class NodeIt {

      friend class Path;

      friend class EdgeIt;

      size_t idx;

      bool tail;  // Is this node the tail of the edge with same idx?

    public:

      // FIXME: jarna neki ilyen is...

      // NodeIt(Invalid);

      bool operator==(const NodeIt& n) const { return idx==n.idx; }

      bool operator!=(const NodeIt& n) const { return idx!=n.idx; }

      bool operator<(const NodeIt& n) const { return idx<n.idx; }

    };

  private:

    bool edgeIncident(const GraphEdge &e, const GraphNode &a,

		      GraphNode &b);

    bool connectTwoEdges(const GraphEdge &e, const GraphEdge &f);

  };

  template<typename Gr>

  typename Path<Gr>::EdgeIt&

  Path<Gr>::next(Path::EdgeIt &e) const {

    if( e.it == edges.end() ) 

      return e;

    GraphNode common_node = ( e.forw ? G.head(*e.it) : G.tail(*e.it) );

    ++e.it;

    // Invalid edgeit is always forward :)

    if( e.it == edges.end() ) {

      e.forw = true;

      return e;

    }

    e.forw = ( G.tail(*e.it) == common_node );

    return e;

  }

  template<typename Gr>

  typename Path<Gr>::NodeIt& Path<Gr>::next(NodeIt &n) const {

    if( n.idx >= length() ) {

      // FIXME: invalid

      n.idx = length()+1;

      return n;

    }

    GraphNode next_node = ( n.tail ? G.head(edges[n.idx]) :

			      G.tail(edges[n.idx]) );

    ++n.idx;

    if( n.idx < length() ) {

      n.tail = ( next_node == G.tail(edges[n.idx]) );

    }

    else {

      n.tail = true;

    }

    return n;

  }

  template<typename Gr>

  bool Path<Gr>::edgeIncident(const GraphEdge &e, const GraphNode &a,

			  GraphNode &b) {

    if( G.tail(e) == a ) {

      b=G.head(e);

      return true;

    }

    if( G.head(e) == a ) {

      b=G.tail(e);

      return true;

    }

    return false;

  }

  template<typename Gr>

  bool Path<Gr>::connectTwoEdges(const GraphEdge &e,

			     const GraphEdge &f) {

    if( edgeIncident(f, G.tail(e), _last) ) {

      _first = G.head(e);

      return true;

    }

    if( edgeIncident(f, G.head(e), _last) ) {

      _first = G.tail(e);

      return true;

    }

    return false;

  }

  template<typename Gr>

  bool Path<Gr>::pushFront(const GraphEdge &e) {

    if( G.valid(_first) ) {

	if( edgeIncident(e, _first, _first) ) {

	  edges.push_front(e);

	  return true;

	}

	else

	  return false;

    }

    else if( length() < 1 || connectTwoEdges(e, edges[0]) ) {

      edges.push_front(e);

      return true;

    }

    else

      return false;

  }

  template<typename Gr>

  bool Path<Gr>::pushBack(const GraphEdge &e) {

    if( G.valid(_last) ) {

	if( edgeIncident(e, _last, _last) ) {

	  edges.push_back(e);

	  return true;

	}

	else

	  return false;

    }

    else if( length() < 1 || connectTwoEdges(edges[0], e) ) {

      edges.push_back(e);

      return true;

    }

    else

      return false;

  }

  template<typename Gr>

  bool Path<Gr>::setFrom(const GraphNode &n) {

    if( G.valid(_first) ) {

      return _first == n;

    }

    else {

      if( length() > 0) {

	if( edgeIncident(edges[0], n, _last) ) {

	  _first = n;

	  return true;

	}

	else return false;

      }

      else {

	_first = _last = n;

	return true;

      }

    }

  }

  template<typename Gr>

  bool Path<Gr>::setTo(const GraphNode &n) {

    if( G.valid(_last) ) {

      return _last == n;

    }

    else {

      if( length() > 0) {

	if( edgeIncident(edges[0], n, _first) ) {

	  _last = n;

	  return true;

	}

	else return false;

      }

      else {

	_first = _last = n;

	return true;

      }

    }

  }

  template<typename Gr>

  typename Path<Gr>::NodeIt

  Path<Gr>::tail(const EdgeIt& e) const {

    NodeIt n;

    if( e.it == edges.end() ) {

      // FIXME: invalid-> invalid

      n.idx = length() + 1;

      n.tail = true;

      return n;

    }

    n.idx = e.it-edges.begin();

    n.tail = e.forw;

    return n;

  }

  template<typename Gr>

  typename Path<Gr>::NodeIt

  Path<Gr>::head(const EdgeIt& e) const {

    if( e.it == edges.end()-1 ) {

      return _last;

    }

    EdgeIt next_edge = e;

    next(next_edge);

    return tail(next_edge);

  }

  template<typename Gr>

  typename Path<Gr>::GraphEdge

  Path<Gr>::graphEdge(const EdgeIt& e) const {

    if( e.it != edges.end() ) {

      return *e.it;

    }

    else {

      return INVALID;

    }

  }

  template<typename Gr>

  typename Path<Gr>::GraphNode

  Path<Gr>::graphNode(const NodeIt& n) const {

    if( n.idx < length() ) {

      return n.tail ? G.tail(edges[n.idx]) : G.head(edges[n.idx]);

    }

    else if( n.idx == length() ) {

      return _last;

    }

    else {

      return INVALID;

    }

  }

  template<typename Gr>

  typename Path<Gr>::EdgeIt& Path<Gr>::nth(EdgeIt &e, size_t k) const {

    if( k<0 || k>=length() ) {

      // FIXME: invalid EdgeIt

      e.it = edges.end();

      e.forw = true;

      return e;

    }

    e.it = edges.begin()+k;

    if(k==0) {

      e.forw = ( G.tail(*e.it) == _first );

    }

    else {

      e.forw = ( G.tail(*e.it) == G.tail(edges[k-1]) ||

		 G.tail(*e.it) == G.head(edges[k-1]) );

    }

    return e;

  }

  template<typename Gr>

  typename Path<Gr>::NodeIt& Path<Gr>::nth(NodeIt &n, size_t k) const {

    if( k<0 || k>length() ) {

      // FIXME: invalid NodeIt

      n.idx = length()+1;

      n.tail = true;

      return n;

    }

    if( k==length() ) {

      n.idx = length();

      n.tail = true;

      return n;

    }

    n = tail(nth<EdgeIt>(k));

    return n;

  }

  // Reszut konstruktorok:

  template<typename Gr>

  Path<Gr>::Path(const Path &P, const EdgeIt &a, const EdgeIt &b) :

    G(P.G), edges(a.it, b.it)    // WARNING: if b.it < a.it this will blow up! 

  {

    if( G.valid(P._first) && a.it < P.edges.end() ) {

      _first = ( a.forw ? G.tail(*a.it) : G.head(*a.it) );

      if( b.it < P.edges.end() ) {

	_last = ( b.forw ? G.tail(*b.it) : G.head(*b.it) );

      }

      else {

	_last = P._last;

      }

    }

  }

  template<typename Gr>

  Path<Gr>::Path(const Path &P, const NodeIt &a, const NodeIt &b) :

    G(P.G)

  {

    if( !P.valid(a) || !P.valid(b) )

      return;

    int ai = a.idx, bi = b.idx;

    if( bi<ai )

      swap(ai,bi);

    edges.resize(bi-ai);

    copy(P.edges.begin()+ai, P.edges.begin()+bi, edges.begin());

    _first = P.graphNode(a);

    _last = P.graphNode(b);

  }

} // namespace hugo

#endif // HUGO_PATH_H