/* -*- 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 lemon_io

///\file

///\brief Lemon Graph Format writer.

#ifndef LEMON_LGF_WRITER_H

#define LEMON_LGF_WRITER_H

#include <iostream>

#include <fstream>

#include <sstream>

#include <algorithm>

#include <vector>

#include <functional>

#include <lemon/assert.h>

#include <lemon/graph_utils.h>

namespace lemon {

  namespace _writer_bits {

    template <typename Value>

    struct DefaultConverter {

      std::string operator()(const Value& value) {

	std::ostringstream os;

	os << value;

	return os.str();

      }

    };

    template <typename T>

    bool operator<(const T&, const T&) {

      throw DataFormatError("Label map is not comparable");

    }

    template <typename _Map>

    class MapLess {

    public:

      typedef _Map Map;

      typedef typename Map::Key Item;

    private:

      const Map& _map;

    public:

      MapLess(const Map& map) : _map(map) {}

      bool operator()(const Item& left, const Item& right) {

	return _map[left] < _map[right];

      }

    };

    template <typename _Graph, bool _dir, typename _Map>

    class GraphArcMapLess {

    public:

      typedef _Map Map;

      typedef _Graph Graph;

      typedef typename Graph::Edge Item;

    private:

      const Graph& _graph;

      const Map& _map;

    public:

      GraphArcMapLess(const Graph& graph, const Map& map) 

	: _graph(graph), _map(map) {}

      bool operator()(const Item& left, const Item& right) {

	return _map[_graph.direct(left, _dir)] < 

	  _map[_graph.direct(right, _dir)];

      }

    };

    template <typename _Item>    

    class MapStorageBase {

    public:

      typedef _Item Item;

    public:

      MapStorageBase() {}

      virtual ~MapStorageBase() {}

      virtual std::string get(const Item& item) = 0;

      virtual void sort(std::vector<Item>&) = 0;

    };

    template <typename _Item, typename _Map, 

	      typename _Converter = DefaultConverter<typename _Map::Value> >

    class MapStorage : public MapStorageBase<_Item> {

    public:

      typedef _Map Map;

      typedef _Converter Converter;

      typedef _Item Item;

    private:

      const Map& _map;

      Converter _converter;

    public:

      MapStorage(const Map& map, const Converter& converter = Converter()) 

	: _map(map), _converter(converter) {}

      virtual ~MapStorage() {}

      virtual std::string get(const Item& item) {

	return _converter(_map[item]);

      }

      virtual void sort(std::vector<Item>& items) {

	MapLess<Map> less(_map);

	std::sort(items.begin(), items.end(), less);

      }

    };

    template <typename _Graph, bool _dir, typename _Map, 

	      typename _Converter = DefaultConverter<typename _Map::Value> >

    class GraphArcMapStorage : public MapStorageBase<typename _Graph::Edge> {

    public:

      typedef _Map Map;

      typedef _Converter Converter;

      typedef _Graph Graph;

      typedef typename Graph::Edge Item;

      static const bool dir = _dir;

    private:

      const Graph& _graph;

      const Map& _map;

      Converter _converter;

    public:

      GraphArcMapStorage(const Graph& graph, const Map& map,  

			 const Converter& converter = Converter()) 

	: _graph(graph), _map(map), _converter(converter) {}

      virtual ~GraphArcMapStorage() {}

      virtual std::string get(const Item& item) {

	return _converter(_map[_graph.direct(item, dir)]);

      }

      virtual void sort(std::vector<Item>& items) {

	GraphArcMapLess<Graph, dir, Map> less(_graph, _map);

	std::sort(items.begin(), items.end(), less);

      }

    };

    class ValueStorageBase {

    public:

      ValueStorageBase() {}

      virtual ~ValueStorageBase() {}

      virtual std::string get() = 0;      

    };

    template <typename _Value, typename _Converter = DefaultConverter<_Value> >

    class ValueStorage : public ValueStorageBase {

    public:

      typedef _Value Value;

      typedef _Converter Converter;

    private:

      const Value& _value;

      Converter _converter;

    public:

      ValueStorage(const Value& value, const Converter& converter = Converter())

 	: _value(value), _converter(converter) {}

      virtual std::string get() {

	return _converter(_value);

      }

    };

    template <typename Value>

    struct MapLookUpConverter {

      const std::map<Value, std::string>& _map;

      MapLookUpConverter(const std::map<Value, std::string>& map) 

	: _map(map) {}

      std::string operator()(const Value& str) {

	typename std::map<Value, std::string>::const_iterator it = 

	  _map.find(str);

	if (it == _map.end()) {

	  throw DataFormatError("Item not found");

	}

	return it->second;

      }

    };

    template <typename Graph>

    struct GraphArcLookUpConverter {

      const Graph& _graph;

      const std::map<typename Graph::Edge, std::string>& _map;

      GraphArcLookUpConverter(const Graph& graph, 

			      const std::map<typename Graph::Edge, 

			                     std::string>& map) 

	: _graph(graph), _map(map) {}

      std::string operator()(const typename Graph::Arc& val) {

	typename std::map<typename Graph::Edge, std::string>

	  ::const_iterator it = _map.find(val);

	if (it == _map.end()) {

	  throw DataFormatError("Item not found");

	}

	return (_graph.direction(val) ? '+' : '-') + it->second;

      }

    };

    bool isWhiteSpace(char c) {

      return c == ' ' || c == '\t' || c == '\v' || 

        c == '\n' || c == '\r' || c == '\f'; 

    }

    bool isEscaped(char c) {

      return c == '\\' || c == '\"' || c == '\'' || 

	c == '\a' || c == '\b';

    }

    static void writeEscape(std::ostream& os, char c) {

      switch (c) {

      case '\\':

	os << "\\\\";

	return;

      case '\"':

	os << "\\\"";

	return;

      case '\a':

	os << "\\a";

	return;

      case '\b':

	os << "\\b";

	return;

      case '\f':

	os << "\\f";

	return;

      case '\r':

	os << "\\r";

	return;

      case '\n':

	os << "\\n";

	return;

      case '\t':

	os << "\\t";

	return;

      case '\v':

	os << "\\v";

	return;

      default:

	if (c < 0x20) {

	  std::ios::fmtflags flags = os.flags();

	  os << '\\' << std::oct << static_cast<int>(c);

	  os.flags(flags);

	} else {

	  os << c;

	}

	return;

      }     

    }

    bool requireEscape(const std::string& str) {

      if (str.empty() || str[0] == '@') return true;

      std::istringstream is(str);

      char c;

      while (is.get(c)) {

	if (isWhiteSpace(c) || isEscaped(c)) {

	  return true;

	}

      }

      return false;

    }

    std::ostream& writeToken(std::ostream& os, const std::string& str) {

      if (requireEscape(str)) {

	os << '\"';

	for (std::string::const_iterator it = str.begin(); 

	     it != str.end(); ++it) {

	  writeEscape(os, *it);

	}	

	os << '\"';

      } else {

	os << str;

      }

      return os;

    }

  }

  /// \ingroup lemon_io

  ///  

  /// \brief LGF writer for directed graphs

  ///

  /// This utility writes an \ref lgf-format "LGF" file.

  ///

  /// The writing method does a batch processing. The user creates a

  /// writer object, then various writing rules can be added to the

  /// writer, and eventually the writing is executed with the \c run()

  /// member function. A map writing rule can be added to the writer

  /// with the \c nodeMap() or \c arcMap() members. An optional

  /// converter parameter can also be added as a standard functor

  /// converting from the value type of the map to std::string. If it

  /// is set, it will determine how the map's value type is written to

  /// the output stream. If the functor is not set, then a default

  /// conversion will be used. The \c attribute(), \c node() and \c

  /// arc() functions are used to add attribute writing rules.

  ///

  ///\code

  ///     DigraphWriter<Digraph>(std::cout, digraph).

  ///       nodeMap("coordinates", coord_map).

  ///       nodeMap("size", size).

  ///       nodeMap("title", title).

  ///       arcMap("capacity", cap_map).

  ///       node("source", src).

  ///       node("target", trg).

  ///       attribute("caption", caption).

  ///       run();

  ///\endcode

  ///

  ///

  /// By default, the writer does not write additional captions to the

  /// sections, but they can be give as an optional parameter of

  /// the \c nodes(), \c arcs() or \c

  /// attributes() functions.

  ///

  /// The \c skipNodes() and \c skipArcs() functions forbid the

  /// writing of the sections. If two arc sections should be written

  /// to the output, it can be done in two passes, the first pass

  /// writes the node section and the first arc section, then the

  /// second pass skips the node section and writes just the arc

  /// section to the stream. The output stream can be retrieved with

  /// the \c ostream() function, hence the second pass can append its

  /// output to the output of the first pass.

  template <typename _Digraph>

  class DigraphWriter {

  public:

    typedef _Digraph Digraph;

    TEMPLATE_DIGRAPH_TYPEDEFS(Digraph);

  private:

    std::ostream* _os;

    bool local_os;

    Digraph& _digraph;

    std::string _nodes_caption;

    std::string _arcs_caption;

    std::string _attributes_caption;

    typedef std::map<Node, std::string> NodeIndex;

    NodeIndex _node_index;

    typedef std::map<Arc, std::string> ArcIndex;

    ArcIndex _arc_index;

    typedef std::vector<std::pair<std::string, 

      _writer_bits::MapStorageBase<Node>* > > NodeMaps;    

    NodeMaps _node_maps; 

    typedef std::vector<std::pair<std::string, 

      _writer_bits::MapStorageBase<Arc>* > >ArcMaps;

    ArcMaps _arc_maps;

    typedef std::vector<std::pair<std::string, 

      _writer_bits::ValueStorageBase*> > Attributes;

    Attributes _attributes;

    bool _skip_nodes;

    bool _skip_arcs;

  public:

    /// \brief Constructor

    ///

    /// Construct a directed graph writer, which writes to the given

    /// output stream.

    DigraphWriter(std::ostream& is, Digraph& digraph) 

      : _os(&is), local_os(false), _digraph(digraph),

	_skip_nodes(false), _skip_arcs(false) {}

    /// \brief Constructor

    ///

    /// Construct a directed graph writer, which writes to the given

    /// output file.

    DigraphWriter(const std::string& fn, Digraph& digraph) 

      : _os(new std::ofstream(fn.c_str())), local_os(true), _digraph(digraph),

	_skip_nodes(false), _skip_arcs(false) {}

    /// \brief Constructor

    ///

    /// Construct a directed graph writer, which writes to the given

    /// output file.

    DigraphWriter(const char* fn, Digraph& digraph) 

      : _os(new std::ofstream(fn)), local_os(true), _digraph(digraph),

	_skip_nodes(false), _skip_arcs(false) {}

    /// \brief Copy constructor

    ///

    /// The copy constructor transfers all data from the other writer,

    /// therefore the copied writer will not be usable more. 

    DigraphWriter(DigraphWriter& other) 

      : _os(other._os), local_os(other.local_os), _digraph(other._digraph),

	_skip_nodes(other._skip_nodes), _skip_arcs(other._skip_arcs) {

      other._os = 0;

      other.local_os = false;

      _node_index.swap(other._node_index);

      _arc_index.swap(other._arc_index);

      _node_maps.swap(other._node_maps);

      _arc_maps.swap(other._arc_maps);

      _attributes.swap(other._attributes);

      _nodes_caption = other._nodes_caption;

      _arcs_caption = other._arcs_caption;

      _attributes_caption = other._attributes_caption;

    }

    /// \brief Destructor

    ~DigraphWriter() {

      for (typename NodeMaps::iterator it = _node_maps.begin(); 

	   it != _node_maps.end(); ++it) {

	delete it->second;

      }

      for (typename ArcMaps::iterator it = _arc_maps.begin(); 

	   it != _arc_maps.end(); ++it) {

	delete it->second;

      }

      for (typename Attributes::iterator it = _attributes.begin(); 

	   it != _attributes.end(); ++it) {

	delete it->second;

      }

      if (local_os) {

	delete _os;

      }

    }

  private:

    DigraphWriter& operator=(const DigraphWriter&);

  public:

    /// \name Writing rules

    /// @{

    /// \brief Node map reading rule

    ///

    /// Add a node map reading rule to the writer.

    template <typename Map>

    DigraphWriter& nodeMap(const std::string& caption, const Map& map) {

      checkConcept<concepts::ReadMap<Node, typename Map::Value>, Map>();

      _writer_bits::MapStorageBase<Node>* storage = 

	new _writer_bits::MapStorage<Node, Map>(map);

      _node_maps.push_back(std::make_pair(caption, storage));

      return *this;

    }

    /// \brief Node map writing rule

    ///

    /// Add a node map writing rule with specialized converter to the

    /// writer.

    template <typename Map, typename Converter>

    DigraphWriter& nodeMap(const std::string& caption, const Map& map, 

			   const Converter& converter = Converter()) {

      checkConcept<concepts::ReadMap<Node, typename Map::Value>, Map>();

      _writer_bits::MapStorageBase<Node>* storage = 

	new _writer_bits::MapStorage<Node, Map, Converter>(map, converter);

      _node_maps.push_back(std::make_pair(caption, storage));

      return *this;

    }

    /// \brief Arc map writing rule

    ///

    /// Add an arc map writing rule to the writer.

    template <typename Map>

    DigraphWriter& arcMap(const std::string& caption, const Map& map) {

      checkConcept<concepts::ReadMap<Arc, typename Map::Value>, Map>();

      _writer_bits::MapStorageBase<Arc>* storage = 

	new _writer_bits::MapStorage<Arc, Map>(map);

      _arc_maps.push_back(std::make_pair(caption, storage));

      return *this;

    }

    /// \brief Arc map writing rule

    ///

    /// Add an arc map writing rule with specialized converter to the

    /// writer.

    template <typename Map, typename Converter>

    DigraphWriter& arcMap(const std::string& caption, const Map& map, 

			  const Converter& converter = Converter()) {

      checkConcept<concepts::ReadMap<Arc, typename Map::Value>, Map>();

      _writer_bits::MapStorageBase<Arc>* storage = 

	new _writer_bits::MapStorage<Arc, Map, Converter>(map, converter);

      _arc_maps.push_back(std::make_pair(caption, storage));

      return *this;

    }

    /// \brief Attribute writing rule

    ///

    /// Add an attribute writing rule to the writer.

    template <typename Value>

    DigraphWriter& attribute(const std::string& caption, const Value& value) {

      _writer_bits::ValueStorageBase* storage = 

	new _writer_bits::ValueStorage<Value>(value);

      _attributes.push_back(std::make_pair(caption, storage));

      return *this;

    }

    /// \brief Attribute writing rule

    ///

    /// Add an attribute writing rule with specialized converter to the

    /// writer.

    template <typename Value, typename Converter>

    DigraphWriter& attribute(const std::string& caption, const Value& value, 

			     const Converter& converter = Converter()) {

      _writer_bits::ValueStorageBase* storage = 

	new _writer_bits::ValueStorage<Value, Converter>(value, converter);

      _attributes.push_back(std::make_pair(caption, storage));

      return *this;

    }

    /// \brief Node writing rule

    ///

    /// Add a node writing rule to the writer.

    DigraphWriter& node(const std::string& caption, const Node& node) {

      typedef _writer_bits::MapLookUpConverter<Node> Converter;

      Converter converter(_node_index);

      _writer_bits::ValueStorageBase* storage = 

	new _writer_bits::ValueStorage<Node, Converter>(node, converter);

      _attributes.push_back(std::make_pair(caption, storage));

      return *this;

    }

    /// \brief Arc writing rule

    ///

    /// Add an arc writing rule to writer.

    DigraphWriter& arc(const std::string& caption, const Arc& arc) {

      typedef _writer_bits::MapLookUpConverter<Arc> Converter;

      Converter converter(_arc_index);

      _writer_bits::ValueStorageBase* storage = 

	new _writer_bits::ValueStorage<Arc, Converter>(arc, converter);

      _attributes.push_back(std::make_pair(caption, storage));

      return *this;

    }

    /// \name Select section by name

    /// @{

    /// \brief Set \c \@nodes section to be read

    ///

    /// Set \c \@nodes section to be read

    DigraphWriter& nodes(const std::string& caption) {

      _nodes_caption = caption;

      return *this;

    }

    /// \brief Set \c \@arcs section to be read

    ///

    /// Set \c \@arcs section to be read

    DigraphWriter& arcs(const std::string& caption) {

      _arcs_caption = caption;

      return *this;

    }

    /// \brief Set \c \@attributes section to be read

    ///

    /// Set \c \@attributes section to be read

    DigraphWriter& attributes(const std::string& caption) {

      _attributes_caption = caption;

      return *this;

    }

    /// \name Skipping section

    /// @{

    /// \brief Skip writing the node set

    ///

    /// The \c \@nodes section will be not written to the stream.

    DigraphWriter& skipNodes() {

      LEMON_ASSERT(!_skip_nodes, "Multiple usage of skipNodes() member");

      _skip_nodes = true;

      return *this;

    }

    /// \brief Skip writing arc set

    ///

    /// The \c \@arcs section will be not written to the stream.

    DigraphWriter& skipArcs() {

      LEMON_ASSERT(!_skip_arcs, "Multiple usage of skipArcs() member");

      _skip_arcs = true;

      return *this;

    }

    /// @}

  private:

    void writeNodes() {

      _writer_bits::MapStorageBase<Node>* label = 0;

      for (typename NodeMaps::iterator it = _node_maps.begin();

	   it != _node_maps.end(); ++it) {

        if (it->first == "label") {

	  label = it->second;

	  break;

	}

      }

      *_os << "@nodes";

      if (!_nodes_caption.empty()) {

	_writer_bits::writeToken(*_os << ' ', _nodes_caption);

      }

      *_os << std::endl;

      if (label == 0) {

	*_os << "label" << '\t';

      }

      for (typename NodeMaps::iterator it = _node_maps.begin();

	   it != _node_maps.end(); ++it) {

	_writer_bits::writeToken(*_os, it->first) << '\t';

      }

      *_os << std::endl;

      std::vector<Node> nodes;

      for (NodeIt n(_digraph); n != INVALID; ++n) {

	nodes.push_back(n);

      }

      if (label == 0) {

	IdMap<Digraph, Node> id_map(_digraph);

	_writer_bits::MapLess<IdMap<Digraph, Node> > id_less(id_map);

	std::sort(nodes.begin(), nodes.end(), id_less);

      } else {

	label->sort(nodes);

      }

      for (int i = 0; i < static_cast<int>(nodes.size()); ++i) {

	Node n = nodes[i];

	if (label == 0) {

	  std::ostringstream os;

	  os << _digraph.id(n);

	  _writer_bits::writeToken(*_os, os.str());

	  *_os << '\t';

	  _node_index.insert(std::make_pair(n, os.str()));

	}

	for (typename NodeMaps::iterator it = _node_maps.begin();

	     it != _node_maps.end(); ++it) {

	  std::string value = it->second->get(n);

	  _writer_bits::writeToken(*_os, value);

	  if (it->first == "label") {

	    _node_index.insert(std::make_pair(n, value));

	  }

	  *_os << '\t';

	}

	*_os << std::endl;

      }

    }

    void createNodeIndex() {

      _writer_bits::MapStorageBase<Node>* label = 0;

      for (typename NodeMaps::iterator it = _node_maps.begin();

	   it != _node_maps.end(); ++it) {

        if (it->first == "label") {

	  label = it->second;

	  break;

	}

      }

      if (label == 0) {

	for (NodeIt n(_digraph); n != INVALID; ++n) {

	  std::ostringstream os;

	  os << _digraph.id(n);

	  _node_index.insert(std::make_pair(n, os.str()));	  

	}	

      } else {

	for (NodeIt n(_digraph); n != INVALID; ++n) {

	  std::string value = label->get(n);	  

	  _node_index.insert(std::make_pair(n, value));

	}

      }

    }

    void writeArcs() {

      _writer_bits::MapStorageBase<Arc>* label = 0;

      for (typename ArcMaps::iterator it = _arc_maps.begin();

	   it != _arc_maps.end(); ++it) {

        if (it->first == "label") {

	  label = it->second;

	  break;

	}

      }

      *_os << "@arcs";

      if (!_arcs_caption.empty()) {

	_writer_bits::writeToken(*_os << ' ', _arcs_caption);

      }

      *_os << std::endl;

      *_os << '\t' << '\t';

      if (label == 0) {

	*_os << "label" << '\t';

      }

      for (typename ArcMaps::iterator it = _arc_maps.begin();

	   it != _arc_maps.end(); ++it) {

	_writer_bits::writeToken(*_os, it->first) << '\t';

      }

      *_os << std::endl;

      std::vector<Arc> arcs;

      for (ArcIt n(_digraph); n != INVALID; ++n) {

	arcs.push_back(n);

      }

      if (label == 0) {

	IdMap<Digraph, Arc> id_map(_digraph);

	_writer_bits::MapLess<IdMap<Digraph, Arc> > id_less(id_map);

	std::sort(arcs.begin(), arcs.end(), id_less);

      } else {

	label->sort(arcs);

      }

      for (int i = 0; i < static_cast<int>(arcs.size()); ++i) {

	Arc a = arcs[i];

	_writer_bits::writeToken(*_os, _node_index.

				 find(_digraph.source(a))->second);

	*_os << '\t';

	_writer_bits::writeToken(*_os, _node_index.

				 find(_digraph.target(a))->second);

	*_os << '\t';

	if (label == 0) {

	  std::ostringstream os;

	  os << _digraph.id(a);

	  _writer_bits::writeToken(*_os, os.str());

	  *_os << '\t';

	  _arc_index.insert(std::make_pair(a, os.str()));

	}

	for (typename ArcMaps::iterator it = _arc_maps.begin();

	     it != _arc_maps.end(); ++it) {

	  std::string value = it->second->get(a);

	  _writer_bits::writeToken(*_os, value);

	  if (it->first == "label") {

	    _arc_index.insert(std::make_pair(a, value));

	  }

	  *_os << '\t';

	}

	*_os << std::endl;

      }

    }

    void createArcIndex() {

      _writer_bits::MapStorageBase<Arc>* label = 0;

      for (typename ArcMaps::iterator it = _arc_maps.begin();

	   it != _arc_maps.end(); ++it) {

        if (it->first == "label") {

	  label = it->second;

	  break;

	}

      }

      if (label == 0) {

	for (ArcIt a(_digraph); a != INVALID; ++a) {

	  std::ostringstream os;

	  os << _digraph.id(a);

	  _arc_index.insert(std::make_pair(a, os.str()));	  

	}	

      } else {

	for (ArcIt a(_digraph); a != INVALID; ++a) {

	  std::string value = label->get(a);	  

	  _arc_index.insert(std::make_pair(a, value));

	}

      }

    }

    void writeAttributes() {

      if (_attributes.empty()) return;

      *_os << "@attributes";

      if (!_attributes_caption.empty()) {

	_writer_bits::writeToken(*_os << ' ', _attributes_caption);

      }

      *_os << std::endl;

      for (typename Attributes::iterator it = _attributes.begin();

	   it != _attributes.end(); ++it) {

	_writer_bits::writeToken(*_os, it->first) << ' ';

	_writer_bits::writeToken(*_os, it->second->get());

	*_os << std::endl;

      }

    }

  public:

    /// \name Execution of the writer    

    /// @{

    /// \brief Start the batch processing

    ///

    /// This function starts the batch processing

    void run() {

      if (!_skip_nodes) {

	writeNodes();

      } else {

	createNodeIndex();

      }

      if (!_skip_arcs) {      

	writeArcs();

      } else {

	createArcIndex();

      }

      writeAttributes();

    }

    /// \brief Gives back the stream of the writer

    ///

    /// Gives back the stream of the writer

    std::ostream& ostream() {

      return *_os;

    }

    /// @}

  };

  /// \relates DigraphWriter

  template <typename Digraph>

  DigraphWriter<Digraph> digraphWriter(std::ostream& os, Digraph& digraph) {

    DigraphWriter<Digraph> tmp(os, digraph);

    return tmp;

  }

  /// \relates DigraphWriter

  template <typename Digraph>

  DigraphWriter<Digraph> digraphWriter(const std::string& fn, 

				       Digraph& digraph) {

    DigraphWriter<Digraph> tmp(fn, digraph);

    return tmp;

  }

  /// \relates DigraphWriter

  template <typename Digraph>

  DigraphWriter<Digraph> digraphWriter(const char* fn, Digraph& digraph) {

    DigraphWriter<Digraph> tmp(fn, digraph);

    return tmp;

  }

  /// \ingroup lemon_io

  ///  

  /// \brief LGF writer for directed graphs

  ///

  /// This utility writes an \ref lgf-format "LGF" file.

  template <typename _Graph>

  class GraphWriter {

  public:

    typedef _Graph Graph;

    TEMPLATE_GRAPH_TYPEDEFS(Graph);

  private:

    std::ostream* _os;

    bool local_os;

    Graph& _graph;

    std::string _nodes_caption;

    std::string _edges_caption;

    std::string _attributes_caption;

    typedef std::map<Node, std::string> NodeIndex;

    NodeIndex _node_index;

    typedef std::map<Edge, std::string> EdgeIndex;

    EdgeIndex _edge_index;

    typedef std::vector<std::pair<std::string, 

      _writer_bits::MapStorageBase<Node>* > > NodeMaps;    

    NodeMaps _node_maps; 

    typedef std::vector<std::pair<std::string, 

      _writer_bits::MapStorageBase<Edge>* > >EdgeMaps;

    EdgeMaps _edge_maps;

    typedef std::vector<std::pair<std::string, 

      _writer_bits::ValueStorageBase*> > Attributes;

    Attributes _attributes;

    bool _skip_nodes;

    bool _skip_edges;

  public:

    /// \brief Constructor

    ///

    /// Construct a directed graph writer, which writes to the given

    /// output stream.

    GraphWriter(std::ostream& is, Graph& graph) 

      : _os(&is), local_os(false), _graph(graph),

	_skip_nodes(false), _skip_edges(false) {}

    /// \brief Constructor

    ///

    /// Construct a directed graph writer, which writes to the given

    /// output file.

    GraphWriter(const std::string& fn, Graph& graph) 

      : _os(new std::ofstream(fn.c_str())), local_os(true), _graph(graph),

	_skip_nodes(false), _skip_edges(false) {}

    /// \brief Constructor

    ///

    /// Construct a directed graph writer, which writes to the given

    /// output file.

    GraphWriter(const char* fn, Graph& graph) 

      : _os(new std::ofstream(fn)), local_os(true), _graph(graph),

	_skip_nodes(false), _skip_edges(false) {}

    /// \brief Copy constructor

    ///

    /// The copy constructor transfers all data from the other writer,

    /// therefore the copied writer will not be usable more. 

    GraphWriter(GraphWriter& other) 

      : _os(other._os), local_os(other.local_os), _graph(other._graph),

	_skip_nodes(other._skip_nodes), _skip_edges(other._skip_edges) {

      other._os = 0;

      other.local_os = false;

      _node_index.swap(other._node_index);

      _edge_index.swap(other._edge_index);

      _node_maps.swap(other._node_maps);

      _edge_maps.swap(other._edge_maps);

      _attributes.swap(other._attributes);

      _nodes_caption = other._nodes_caption;

      _edges_caption = other._edges_caption;

      _attributes_caption = other._attributes_caption;

    }

    /// \brief Destructor

    ~GraphWriter() {

      for (typename NodeMaps::iterator it = _node_maps.begin(); 

	   it != _node_maps.end(); ++it) {

	delete it->second;

      }

      for (typename EdgeMaps::iterator it = _edge_maps.begin(); 

	   it != _edge_maps.end(); ++it) {

	delete it->second;

      }

      for (typename Attributes::iterator it = _attributes.begin(); 

	   it != _attributes.end(); ++it) {

	delete it->second;

      }

      if (local_os) {

	delete _os;

      }

    }

  private:

    GraphWriter& operator=(const GraphWriter&);

  public:

    /// \name Writing rules

    /// @{

    /// \brief Node map reading rule

    ///

    /// Add a node map reading rule to the writer.