/* -*- C++ -*-
 * lemon/path.h - Part of LEMON, a generic C++ optimization library
 *
 * Copyright (C) 2005 Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
 * (Egervary Research Group on Combinatorial Optimization, EGRES).
 *
 * Permission to use, modify and distribute this software is granted
 * provided that this copyright notice appears in all copies. For
 * precise terms see the accompanying LICENSE file.
 *
 * This software is provided "AS IS" with no warranty of any kind,
 * express or implied, and with no claim as to its suitability for any
 * purpose.
 *
 */

/**
@defgroup paths Path Structures
@ingroup datas
\brief Path structures implemented in LEMON.

LEMON provides flexible data structures
to work with paths.

All of them have the same interface, especially they can be built or extended
using a standard Builder subclass. This make is easy to have e.g. the Dijkstra
algorithm to store its result in any kind of path structure.

\sa lemon::concept::Path

*/

///\ingroup paths
///\file
///\brief Classes for representing paths in graphs.
///
///\todo Iterators have obsolete style

#ifndef LEMON_PATH_H
#define LEMON_PATH_H

#include <deque>
#include <vector>
#include <algorithm>

#include <lemon/invalid.h>

namespace lemon {

  /// \addtogroup paths
  /// @{


  //! \brief A structure for representing directed paths in a graph.
  //!
  //! A structure for representing directed path in a graph.
  //! \param Graph The graph type in which the path is.
  //! \param DM DebugMode, defaults to DefaultDebugMode.
  //!
  //! In a sense, the path can be treated as a graph, for is has \c NodeIt
  //! and \c EdgeIt with the same usage. These types converts to the \c Node
  //! and \c Edge of the original graph.
  //!
  //! \todo Thoroughfully check all the range and consistency tests.
  template<typename Graph>
  class DirPath {
  public:
    /// Edge type of the underlying graph.
    typedef typename Graph::Edge GraphEdge;
    /// Node type of the underlying graph.
    typedef typename Graph::Node GraphNode;
    class NodeIt;
    class EdgeIt;

  protected:
    const Graph *gr;
    typedef std::vector<GraphEdge> Container;
    Container edges;

  public:

    /// \param _G The graph in which the path is.
    ///
    DirPath(const Graph &_G) : gr(&_G) {}

    /// \brief Subpath constructor.
    ///
    /// Subpath defined by two nodes.
    /// \warning It is an error if the two edges are not in order!
    DirPath(const DirPath &P, const NodeIt &a, const NodeIt &b) {
      gr = P.gr;
      edges.insert(edges.end(), P.edges.begin()+a.idx, P.edges.begin()+b.idx);
    }

    /// \brief Subpath constructor.
    ///
    /// Subpath defined by two edges. Contains edges in [a,b)
    /// \warning It is an error if the two edges are not in order!
    DirPath(const DirPath &P, const EdgeIt &a, const EdgeIt &b) {
      gr = P.gr;
      edges.insert(edges.end(), P.edges.begin()+a.idx, P.edges.begin()+b.idx);
    }

    /// Length of the path.
    int length() const { return edges.size(); }
    /// Returns whether the path is empty.
    bool empty() const { return edges.empty(); }

    /// Resets the path to an empty path.
    void clear() { edges.clear(); }

    /// \brief Starting point of the path.
    ///
    /// Starting point of the path.
    /// Returns INVALID if the path is empty.
    GraphNode source() const {
      return empty() ? INVALID : gr->source(edges[0]);
    }
    /// \brief End point of the path.
    ///
    /// End point of the path.
    /// Returns INVALID if the path is empty.
    GraphNode target() const {
      return empty() ? INVALID : gr->target(edges[length()-1]);
    }

    /// \brief Initializes node or edge iterator to point to the first
    /// node or edge.
    ///
    /// \sa nth
    template<typename It>
    It& first(It &i) const { return i=It(*this); }

    /// \brief Initializes node iterator to point to the node of a given index.
    NodeIt& nth(NodeIt &i, int n) const {
      return i=NodeIt(*this, n);
    }

    /// \brief Initializes edge iterator to point to the edge of a given index.
    EdgeIt& nth(EdgeIt &i, int n) const {
      return i=EdgeIt(*this, n);
    }

    /// \brief Returns node iterator pointing to the target node of the
    /// given edge iterator.
    NodeIt target(const EdgeIt& e) const {
      return NodeIt(*this, e.idx+1);
    }

    /// \brief Returns node iterator pointing to the source node of the
    /// given edge iterator.
    NodeIt source(const EdgeIt& e) const {
      return NodeIt(*this, e.idx);
    }


    /* Iterator classes */

    /**
     * \brief Iterator class to iterate on the edges of the paths
     *
     * This class is used to iterate on the edges of the paths
     *
     * Of course it converts to Graph::Edge
     *
     */
    class EdgeIt {
      friend class DirPath;

      int idx;
      const DirPath *p;
    public:
      /// Default constructor
      EdgeIt() {}
      /// Invalid constructor
      EdgeIt(Invalid) : idx(-1), p(0) {}
      /// Constructor with starting point
      EdgeIt(const DirPath &_p, int _idx = 0) :
	idx(_idx), p(&_p) { validate(); }

      ///Validity check
      bool valid() const { return idx!=-1; }

      ///Conversion to Graph::Edge
      operator GraphEdge () const {
	return valid() ? p->edges[idx] : INVALID;
      }

      /// Next edge
      EdgeIt& operator++() { ++idx; validate(); return *this; }

      /// Comparison operator
      bool operator==(const EdgeIt& e) const { return idx==e.idx; }
      /// Comparison operator
      bool operator!=(const EdgeIt& e) const { return idx!=e.idx; }
      /// Comparison operator
      bool operator<(const EdgeIt& e) const { return idx<e.idx; }

    private:
      void validate() { if(idx >= p->length() ) idx=-1; }
    };

    /**
     * \brief Iterator class to iterate on the nodes of the paths
     *
     * This class is used to iterate on the nodes of the paths
     *
     * Of course it converts to Graph::Node
     *
     */
    class NodeIt {
      friend class DirPath;

      int idx;
      const DirPath *p;
    public:
      /// Default constructor
      NodeIt() {}
      /// Invalid constructor
      NodeIt(Invalid) : idx(-1), p(0) {}
      /// Constructor with starting point
      NodeIt(const DirPath &_p, int _idx = 0) :
	idx(_idx), p(&_p) { validate(); }

      ///Validity check
      bool valid() const { return idx!=-1; }

      ///Conversion to Graph::Node
      operator const GraphNode& () const {
	if(idx >= p->length())
	  return p->target();
	else if(idx >= 0)
	  return p->gr->source(p->edges[idx]);
	else
	  return INVALID;
      }
      /// Next node
      NodeIt& operator++() { ++idx; validate(); return *this; }

      /// Comparison operator
      bool operator==(const NodeIt& e) const { return idx==e.idx; }
      /// Comparison operator
      bool operator!=(const NodeIt& e) const { return idx!=e.idx; }
      /// Comparison operator
      bool operator<(const NodeIt& e) const { return idx<e.idx; }

    private:
      void validate() { if(idx > p->length() ) idx=-1; }
    };

    friend class Builder;

    /**
     * \brief Class to build paths
     *
     * This class is used to fill a path with edges.
     *
     * You can push new edges to the front and to the back of the path in
     * arbitrary order then you should commit these changes to the graph.
     *
     * Fundamentally, for most "Paths" (classes fulfilling the
     * PathConcept) while the builder is active (after the first modifying
     * operation and until the commit()) the original Path is in a
     * "transitional" state (operations on it have undefined result). But
     * in the case of DirPath the original path remains unchanged until the
     * commit. However we don't recomend that you use this feature.
     */
    class Builder {
      DirPath &P;
      Container front, back;

    public:
      ///\param _p the path you want to fill in.
      ///
      Builder(DirPath &_p) : P(_p) {}

      /// Sets the starting node of the path.

      /// Sets the starting node of the path. Edge added to the path
      /// afterwards have to be incident to this node.
      /// It should be called if and only if
      /// the path is empty and before any call to
      /// \ref pushFront() or \ref pushBack()
      void setStartNode(const GraphNode &) {}

      ///Push a new edge to the front of the path

      ///Push a new edge to the front of the path.
      ///\sa setStartNode
      void pushFront(const GraphEdge& e) {
	front.push_back(e);
      }

      ///Push a new edge to the back of the path

      ///Push a new edge to the back of the path.
      ///\sa setStartNode
      void pushBack(const GraphEdge& e) {
	back.push_back(e);
      }

      ///Commit the changes to the path.
      void commit() {
	if( !front.empty() || !back.empty() ) {
	  Container tmp;
	  tmp.reserve(front.size()+back.size()+P.length());
	  tmp.insert(tmp.end(), front.rbegin(), front.rend());
	  tmp.insert(tmp.end(), P.edges.begin(), P.edges.end());
	  tmp.insert(tmp.end(), back.begin(), back.end());
	  P.edges.swap(tmp);
	  front.clear();
	  back.clear();
	}
      }

      ///Reserve storage for the builder in advance.

      ///If you know a reasonable upper bound of the number of the edges
      ///to add to the front, using this function you can speed up the building.

      void reserveFront(size_t r) {front.reserve(r);}

      ///Reserve storage for the builder in advance.

      ///If you know a reasonable upper bound of the number of the edges
      ///to add to the back, using this function you can speed up the building.

      void reserveBack(size_t r) {back.reserve(r);}

    private:
      bool empty() {
	return front.empty() && back.empty() && P.empty();
      }

      GraphNode source() const {
	if( ! front.empty() )
	  return P.gr->source(front[front.size()-1]);
	else if( ! P.empty() )
	  return P.gr->source(P.edges[0]);
	else if( ! back.empty() )
	  return P.gr->source(back[0]);
	else
	  return INVALID;
      }
      GraphNode target() const {
	if( ! back.empty() )
	  return P.gr->target(back[back.size()-1]);
	else if( ! P.empty() )
	  return P.gr->target(P.edges[P.length()-1]);
	else if( ! front.empty() )
	  return P.gr->target(front[0]);
	else
	  return INVALID;
      }

    };

  };










  /**********************************************************************/


  //! \brief A structure for representing undirected path in a graph.
  //!
  //! A structure for representing undirected path in a graph. Ie. this is
  //! a path in a \e directed graph but the edges should not be directed
  //! forward.
  //!
  //! \param Graph The graph type in which the path is.
  //! \param DM DebugMode, defaults to DefaultDebugMode.
  //!
  //! In a sense, the path can be treated as a graph, for is has \c NodeIt
  //! and \c EdgeIt with the same usage. These types converts to the \c Node
  //! and \c Edge of the original graph.
  //!
  //! \todo Thoroughfully check all the range and consistency tests.
  template<typename Graph>
  class UndirPath {
  public:
    /// Edge type of the underlying graph.
    typedef typename Graph::Edge GraphEdge;
     /// Node type of the underlying graph.
   typedef typename Graph::Node GraphNode;
    class NodeIt;
    class EdgeIt;

  protected:
    const Graph *gr;
    typedef std::vector<GraphEdge> Container;
    Container edges;

  public:

    /// \param _G The graph in which the path is.
    ///
    UndirPath(const Graph &_G) : gr(&_G) {}

    /// \brief Subpath constructor.
    ///
    /// Subpath defined by two nodes.
    /// \warning It is an error if the two edges are not in order!
    UndirPath(const UndirPath &P, const NodeIt &a, const NodeIt &b) {
      gr = P.gr;
      edges.insert(edges.end(), P.edges.begin()+a.idx, P.edges.begin()+b.idx);
    }

    /// \brief Subpath constructor.
    ///
    /// Subpath defined by two edges. Contains edges in [a,b)
    /// \warning It is an error if the two edges are not in order!
    UndirPath(const UndirPath &P, const EdgeIt &a, const EdgeIt &b) {
      gr = P.gr;
      edges.insert(edges.end(), P.edges.begin()+a.idx, P.edges.begin()+b.idx);
    }

    /// Length of the path.
    size_t length() const { return edges.size(); }
    /// Returns whether the path is empty.
    bool empty() const { return edges.empty(); }

    /// Resets the path to an empty path.
    void clear() { edges.clear(); }

    /// \brief Starting point of the path.
    ///
    /// Starting point of the path.
    /// Returns INVALID if the path is empty.
    GraphNode source() const {
      return empty() ? INVALID : gr->source(edges[0]);
    }
    /// \brief End point of the path.
    ///
    /// End point of the path.
    /// Returns INVALID if the path is empty.
    GraphNode target() const {
      return empty() ? INVALID : gr->target(edges[length()-1]);
    }

    /// \brief Initializes node or edge iterator to point to the first
    /// node or edge.
    ///
    /// \sa nth
    template<typename It>
    It& first(It &i) const { return i=It(*this); }

    /// \brief Initializes node iterator to point to the node of a given index.
    NodeIt& nth(NodeIt &i, int n) const {
      return i=NodeIt(*this, n);
    }

    /// \brief Initializes edge iterator to point to the edge of a given index.
    EdgeIt& nth(EdgeIt &i, int n) const {
      return i=EdgeIt(*this, n);
    }

    /// Checks validity of a node or edge iterator.
    template<typename It>
    static
    bool valid(const It &i) { return i.valid(); }

    /// Steps the given node or edge iterator.
    template<typename It>
    static
    It& next(It &e) {
      return ++e;
    }

    /// \brief Returns node iterator pointing to the target node of the
    /// given edge iterator.
    NodeIt target(const EdgeIt& e) const {
      return NodeIt(*this, e.idx+1);
    }

    /// \brief Returns node iterator pointing to the source node of the
    /// given edge iterator.
    NodeIt source(const EdgeIt& e) const {
      return NodeIt(*this, e.idx);
    }



    /**
     * \brief Iterator class to iterate on the edges of the paths
     *
     * This class is used to iterate on the edges of the paths
     *
     * Of course it converts to Graph::Edge
     *
     * \todo Its interface differs from the standard edge iterator.
     * Yes, it shouldn't.
     */
    class EdgeIt {
      friend class UndirPath;

      int idx;
      const UndirPath *p;
    public:
      /// Default constructor
      EdgeIt() {}
      /// Invalid constructor
      EdgeIt(Invalid) : idx(-1), p(0) {}
      /// Constructor with starting point
      EdgeIt(const UndirPath &_p, int _idx = 0) :
	idx(_idx), p(&_p) { validate(); }

      ///Validity check
      bool valid() const { return idx!=-1; }

      ///Conversion to Graph::Edge
      operator GraphEdge () const {
	return valid() ? p->edges[idx] : INVALID;
      }
      /// Next edge
     EdgeIt& operator++() { ++idx; validate(); return *this; }

      /// Comparison operator
      bool operator==(const EdgeIt& e) const { return idx==e.idx; }
      /// Comparison operator
      bool operator!=(const EdgeIt& e) const { return idx!=e.idx; }
      /// Comparison operator
      bool operator<(const EdgeIt& e) const { return idx<e.idx; }

    private:
      // FIXME: comparison between signed and unsigned...
      // Jo ez igy? Vagy esetleg legyen a length() int?
      void validate() { if( size_t(idx) >= p->length() ) idx=-1; }
    };

    /**
     * \brief Iterator class to iterate on the nodes of the paths
     *
     * This class is used to iterate on the nodes of the paths
     *
     * Of course it converts to Graph::Node
     *
     * \todo Its interface differs from the standard node iterator.
     * Yes, it shouldn't.
     */
    class NodeIt {
      friend class UndirPath;

      int idx;
      const UndirPath *p;
    public:
      /// Default constructor
      NodeIt() {}
      /// Invalid constructor
      NodeIt(Invalid) : idx(-1), p(0) {}
      /// Constructor with starting point
      NodeIt(const UndirPath &_p, int _idx = 0) :
	idx(_idx), p(&_p) { validate(); }

      ///Validity check
      bool valid() const { return idx!=-1; }

      ///Conversion to Graph::Node
      operator const GraphNode& () const {
	if(idx >= p->length())
	  return p->target();
	else if(idx >= 0)
	  return p->gr->source(p->edges[idx]);
	else
	  return INVALID;
      }
      /// Next node
      NodeIt& operator++() { ++idx; validate(); return *this; }

      /// Comparison operator
      bool operator==(const NodeIt& e) const { return idx==e.idx; }
      /// Comparison operator
      bool operator!=(const NodeIt& e) const { return idx!=e.idx; }
       /// Comparison operator
     bool operator<(const NodeIt& e) const { return idx<e.idx; }

    private:
      void validate() { if( size_t(idx) > p->length() ) idx=-1; }
    };

    friend class Builder;

    /**
     * \brief Class to build paths
     *
     * This class is used to fill a path with edges.
     *
     * You can push new edges to the front and to the back of the path in
     * arbitrary order then you should commit these changes to the graph.
     *
     * Fundamentally, for most "Paths" (classes fulfilling the
     * PathConcept) while the builder is active (after the first modifying
     * operation and until the commit()) the original Path is in a
     * "transitional" state (operations ot it have undefined result). But
     * in the case of UndirPath the original path is unchanged until the
     * commit. However we don't recomend that you use this feature.
     */
    class Builder {
      UndirPath &P;
      Container front, back;

    public:
      ///\param _p the path you want to fill in.
      ///
      Builder(UndirPath &_p) : P(_p) {}

      /// Sets the starting node of the path.

      /// Sets the starting node of the path. Edge added to the path
      /// afterwards have to be incident to this node.
      /// It should be called if and only if
      /// the path is empty and before any call to
      /// \ref pushFront() or \ref pushBack()
      void setStartNode(const GraphNode &) {}

      ///Push a new edge to the front of the path

      ///Push a new edge to the front of the path.
      ///\sa setStartNode
      void pushFront(const GraphEdge& e) {
	front.push_back(e);
      }

      ///Push a new edge to the back of the path

      ///Push a new edge to the back of the path.
      ///\sa setStartNode
      void pushBack(const GraphEdge& e) {
	back.push_back(e);
      }

      ///Commit the changes to the path.
      void commit() {
	if( !(front.empty() && back.empty()) ) {
	  Container tmp;
	  tmp.reserve(front.size()+back.size()+P.length());
	  tmp.insert(tmp.end(), front.rbegin(), front.rend());
	  tmp.insert(tmp.end(), P.edges.begin(), P.edges.end());
	  tmp.insert(tmp.end(), back.begin(), back.end());
	  P.edges.swap(tmp);
	  front.clear();
	  back.clear();
	}
      }


      ///Reserve storage for the builder in advance.

      ///If you know a reasonable upper bound of the number of the edges
      ///to add to the front, using this function you can speed up the building.

      void reserveFront(size_t r) {front.reserve(r);}

      ///Reserve storage for the builder in advance.

      ///If you know a reasonable upper bound of the number of the edges
      ///to add to the back, using this function you can speed up the building.

      void reserveBack(size_t r) {back.reserve(r);}

    private:
      bool empty() {
	return front.empty() && back.empty() && P.empty();
      }

      GraphNode source() const {
	if( ! front.empty() )
	  return P.gr->source(front[front.size()-1]);
	else if( ! P.empty() )
	  return P.gr->source(P.edges[0]);
	else if( ! back.empty() )
	  return P.gr->source(back[0]);
	else
	  return INVALID;
      }
      GraphNode target() const {
	if( ! back.empty() )
	  return P.gr->target(back[back.size()-1]);
	else if( ! P.empty() )
	  return P.gr->target(P.edges[P.length()-1]);
	else if( ! front.empty() )
	  return P.gr->target(front[0]);
	else
	  return INVALID;
      }

    };

  };


  ///@}

} // namespace lemon

#endif // LEMON_PATH_H