/* -*- C++ -*-

 *

 * This file is a part of LEMON, a generic C++ optimization library

 *

 * Copyright (C) 2003-2008

 * 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.

 *

 */

///\ingroup paths

///\file

///\brief Classes for representing paths in digraphs.

///

#ifndef LEMON_PATH_UTILS_H

#define LEMON_PATH_UTILS_H

#include <lemon/concepts/path.h>

namespace lemon {

  namespace _path_bits {

    template <typename Path, typename Enable = void>

    struct RevTagIndicator {

      static const bool value = false;

    };

    template <typename Digraph>

    struct RevTagIndicator<

      Digraph, 

      typename enable_if<typename Digraph::RevTag, void>::type

    > {

      static const bool value = true;

    };

    template <typename Target, typename Source,

              typename BuildEnable = void, typename RevEnable = void>

    struct PathCopySelector {

      static void copy(Target& target, const Source& source) {

        target.clear();

        for (typename Source::ArcIt it(source); it != INVALID; ++it) {

          target.addBack(it);

        }

      }

    };

    template <typename Target, typename Source, typename BuildEnable>

    struct PathCopySelector<

      Target, Source, BuildEnable, 

      typename enable_if<typename Source::RevPathTag, void>::type> {

      static void copy(Target& target, const Source& source) {

        target.clear();

        for (typename Source::RevArcIt it(source); it != INVALID; ++it) {

          target.addFront(it);

        }

      }

    };

    template <typename Target, typename Source, typename RevEnable>

    struct PathCopySelector<

      Target, Source, 

      typename enable_if<typename Target::BuildTag, void>::type, RevEnable> {

      static void copy(Target& target, const Source& source) {

        target.clear();

        target.build(source);

      }

    };

    template <typename Target, typename Source>

    struct PathCopySelector<

      Target, Source, 

      typename enable_if<typename Target::BuildTag, void>::type,

      typename enable_if<typename Source::RevPathTag, void>::type> {

      static void copy(Target& target, const Source& source) {

        target.clear();

        target.buildRev(source);

      }

    };

  }

  /// \brief Make a copy of a path.

  ///

  ///  This function makes a copy of a path.

  template <typename Target, typename Source>

  void copyPath(Target& target, const Source& source) {

    checkConcept<concepts::PathDumper<typename Source::Digraph>, Source>();

    _path_bits::PathCopySelector<Target, Source>::copy(target, source);

  }

  /// \brief Check the consistency of a path.

  ///

  /// This function checks that the target of each arc is the same

  /// as the source of the next one. 

  /// 

  template <typename Digraph, typename Path>

  bool checkPath(const Digraph& digraph, const Path& path) {

    typename Path::ArcIt it(path);

    if (it == INVALID) return true;

    typename Digraph::Node node = digraph.target(it);

    ++it;

    while (it != INVALID) {

      if (digraph.source(it) != node) return false;

      node = digraph.target(it);

      ++it;

    }

    return true;

  }

  /// \brief The source of a path

  ///

  /// This function returns the source of the given path.

  template <typename Digraph, typename Path>

  typename Digraph::Node pathSource(const Digraph& digraph, const Path& path) {

    return digraph.source(path.front());

  }

  /// \brief The target of a path

  ///

  /// This function returns the target of the given path.

  template <typename Digraph, typename Path>

  typename Digraph::Node pathTarget(const Digraph& digraph, const Path& path) {

    return digraph.target(path.back());

  }

  /// \brief Class which helps to iterate through the nodes of a path

  ///

  /// In a sense, the path can be treated as a list of arcs. The

  /// lemon path type stores only this list. As a consequence, it

  /// cannot enumerate the nodes in the path and the zero length paths

  /// cannot have a source node.

  ///

  /// This class implements the node iterator of a path structure. To

  /// provide this feature, the underlying digraph should be passed to

  /// the constructor of the iterator.

  template <typename Path>

  class PathNodeIt {

  private:

    const typename Path::Digraph *_digraph;

    typename Path::ArcIt _it;

    typename Path::Digraph::Node _nd;

  public:

    typedef typename Path::Digraph Digraph;

    typedef typename Digraph::Node Node;

    /// Default constructor

    PathNodeIt() {}

    /// Invalid constructor

    PathNodeIt(Invalid) 

      : _digraph(0), _it(INVALID), _nd(INVALID) {}

    /// Constructor

    PathNodeIt(const Digraph& digraph, const Path& path) 

      : _digraph(&digraph), _it(path) {

      _nd = (_it != INVALID ? _digraph->source(_it) : INVALID);

    }

    /// Constructor

    PathNodeIt(const Digraph& digraph, const Path& path, const Node& src) 

      : _digraph(&digraph), _it(path), _nd(src) {}

    ///Conversion to Digraph::Node

    operator Node() const {

      return _nd;

    }

    /// Next node

    PathNodeIt& operator++() {

      if (_it == INVALID) _nd = INVALID;

      else {

	_nd = _digraph->target(_it);

	++_it;

      }

      return *this;

    }

    /// Comparison operator

    bool operator==(const PathNodeIt& n) const { 

      return _it == n._it && _nd == n._nd; 

    }

    /// Comparison operator

    bool operator!=(const PathNodeIt& n) const { 

      return _it != n._it || _nd != n._nd; 

    }

    /// Comparison operator

    bool operator<(const PathNodeIt& n) const { 

      return (_it < n._it && _nd != INVALID);

    }

  };

}

#endif