/* -*- C++ -*-

 * lemon/lemon_writer.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.

 *

 */

///\ingroup io_group

///\file

///\brief Lemon Format writer.

#ifndef LEMON_LEMON_WRITER_H

#define LEMON_LEMON_WRITER_H

#include <iostream>

#include <fstream>

#include <string>

#include <vector>

#include <algorithm>

#include <map>

#include <memory>

#include <lemon/error.h>

#include <lemon/invalid.h>

#include <lemon/graph_utils.h>

#include <lemon/bits/item_writer.h>

#include <lemon/utility.h>

#include <lemon/maps.h>

#include <lemon/concept_check.h>

#include <lemon/concept/maps.h>

namespace lemon {

  namespace _writer_bits {

    template <typename Item>

    class ItemIdWriter {

    public:

      bool isIdWriter() { return true; }

      void writeId(std::ostream&, const Item&) {}

      template <class _ItemIdWriter>

      struct Constraints {

	void constraints() {

	  bool b = writer.isIdWriter();

	  ignore_unused_variable_warning(b);

	  writer.writeId(os, item);

	}

	_ItemIdWriter& writer;

	std::ostream& os;

	const Item& item;

      };

    };

    template <typename Item>

    class ItemWriter {

    public:

      void write(std::ostream&, const Item&) {}

      template <class _ItemWriter>

      struct Constraints {

	void constraints() {

	  writer.write(os, item);

	}

	_ItemWriter& writer;

	std::ostream& os;

	const Item& item;

      };

    };

  }

  /// \ingroup io_group

  /// \brief Lemon Format writer class.

  /// 

  /// The Lemon Format contains several sections. We do not want to

  /// determine what sections are in a lemon file we give only a framework

  /// to write a section oriented format.

  ///

  /// In the Lemon Format each section starts with a line contains a \c \@

  /// character on the first not white space position. This line is the

  /// header line of the section. Each next lines belong to this section

  /// while it does not starts with \c \@ character. This line can start a 

  /// new section or if it can close the file with the \c \@end line.

  /// The file format ignore the empty lines and it may contain comments

  /// started with a \c # character to the end of the line. 

  ///

  /// The framework provides an abstract LemonWriter::SectionWriter class

  /// what defines the interface of a SectionWriter. The SectionWriter

  /// has the \c header() member function what gives back the header of the

  /// section. After that it will be called the \c write() member which

  /// should write the content of the section.

  ///

  /// \relates GraphWriter

  /// \relates NodeSetWriter

  /// \relates EdgeSetWriter

  /// \relates NodesWriter

  /// \relates EdgesWriter

  /// \relates AttributeWriter

  class LemonWriter {

  public:

    /// \brief Abstract base class for writing a section.

    ///

    /// This class has an \c header() member function what gives back

    /// the header line of the section. The \c write() member should

    /// write the content of the section to the stream.

    class SectionWriter {

      friend class LemonWriter;

    protected:

      /// \brief Constructor for SectionWriter.

      ///

      /// Constructor for SectionWriter. It attach this writer to

      /// the given LemonWriter.

      SectionWriter(LemonWriter& writer) {

	writer.attach(*this);

      }

      virtual ~SectionWriter() {}

      /// \brief The header of section.

      ///

      /// It gives back the header of the section.

      virtual std::string header() = 0;

      /// \brief  Writer function of the section.

      ///

      /// Write the content of the section.

      virtual void write(std::ostream& os) = 0;

    };

    /// \brief Constructor for LemonWriter.

    ///

    /// Constructor for LemonWriter which writes to the given stream.

    LemonWriter(std::ostream& _os) 

      : os(&_os), own_os(false) {}

    /// \brief Constructor for LemonWriter.

    ///

    /// Constructor for LemonWriter which writes to the given file.

    LemonWriter(const std::string& filename) 

      : os(0), own_os(true) {

      os = new std::ofstream(filename.c_str());

    }

    /// \brief Desctructor for LemonWriter.

    ///

    /// Desctructor for LemonWriter.

    ~LemonWriter() {

      if (own_os) {

	delete os;

      }

    }

  private:

    LemonWriter(const LemonWriter&);

    void operator=(const LemonWriter&);

    void attach(SectionWriter& writer) {

      writers.push_back(&writer);

    }

  public:

    /// \brief Executes the LemonWriter.

    /// 

    /// It executes the LemonWriter.

    void run() {

      SectionWriters::iterator it;

      for (it = writers.begin(); it != writers.end(); ++it) {

	*os << (*it)->header() << std::endl;

	(*it)->write(*os);

      }

      *os << "@end" << std::endl;

    }

  private:

    std::ostream* os;

    bool own_os;

    typedef std::vector<SectionWriter*> SectionWriters;

    SectionWriters writers;

  };

  /// \brief Helper class for implementing the common SectionWriters.

  ///

  /// Helper class for implementing the common SectionWriters.

  class CommonSectionWriterBase : public LemonWriter::SectionWriter {

    typedef LemonWriter::SectionWriter Parent;

  protected:

    /// \brief Constructor for CommonSectionWriterBase.

    ///

    /// Constructor for CommonSectionWriterBase. It attach this writer to

    /// the given LemonWriter.

    CommonSectionWriterBase(LemonWriter& _writer) 

      : Parent(_writer) {}

    template <typename _Item>    

    class WriterBase {

    public:

      typedef _Item Item;

      virtual ~WriterBase() {}

      virtual void write(std::ostream& os, const Item& item) = 0;

    };

    template <typename _Item, typename _Map, typename _Writer>

    class MapWriter : public WriterBase<_Item> {

    public:

      typedef _Map Map;

      typedef _Writer Writer;

      typedef typename Writer::Value Value;

      typedef _Item Item;

      typename SmartConstReference<Map>::Type map;

      Writer writer;

      MapWriter(const Map& _map, const Writer& _writer) 

	: map(_map), writer(_writer) {}

      virtual ~MapWriter() {}

      virtual void write(std::ostream& os, const Item& item) {

	Value value = map[item];

	writer.write(os, value);

      }

    };

    class ValueWriterBase {

    public:

      virtual ~ValueWriterBase() {}

      virtual void write(std::ostream&) = 0;

    };

    template <typename _Value, typename _Writer>

    class ValueWriter : public ValueWriterBase {

    public:

      typedef _Value Value;

      typedef _Writer Writer;

      ValueWriter(const Value& _value, const Writer& _writer)

 	: value(_value), writer(_writer) {}

      virtual void write(std::ostream& os) {

	writer.write(os, value);

      }

    private:

      const Value& value;

      Writer writer;

    };

    template <typename _Item>

    class IdWriterBase {

    public:

      typedef _Item Item;

      virtual ~IdWriterBase() {}

      virtual void write(std::ostream&, const Item&) const = 0;

      virtual bool isIdWriter() const = 0;

    };

    template <typename _Item, typename _BoxedIdWriter>

    class IdWriter : public IdWriterBase<_Item> {

    public:

      typedef _Item Item;

      typedef _BoxedIdWriter BoxedIdWriter;

      const BoxedIdWriter& idWriter;

      IdWriter(const BoxedIdWriter& _idWriter) 

	: idWriter(_idWriter) {}

      virtual void write(std::ostream& os, const Item& item) const {

	idWriter.writeId(os, item);

      }

      virtual bool isIdWriter() const {

	return idWriter.isIdWriter();

      }

    };

  };

  /// \ingroup io_group

  /// \brief SectionWriter for writing a graph's nodeset.

  ///

  /// The lemon format can store multiple graph nodesets with several maps.

  /// The nodeset section's header line is \c \@nodeset \c nodeset_id, but the

  /// \c nodeset_id may be empty.

  ///

  /// The first line of the section contains the names of the maps separated

  /// with white spaces. Each next lines describes a node in the nodeset, and

  /// contains the mapped values for each map.

  ///

  /// If the nodeset contains an \c "id" named map then it will be regarded

  /// as id map. This map should contain only unique values and when the 

  /// \c writeId() member will be called with a node it will write it's id.

  /// Otherwise if the \c _forceIdMap constructor parameter is true then

  /// the id map will be the id in the graph.

  ///

  /// \relates LemonWriter

  template <typename _Graph, typename _Traits = DefaultWriterTraits>

  class NodeSetWriter : public CommonSectionWriterBase {

    typedef CommonSectionWriterBase Parent;

  public:

    typedef _Graph Graph;

    typedef _Traits Traits;

    typedef typename Graph::Node Node;

    /// \brief Constructor.

    ///

    /// Constructor for NodeSetWriter. It creates the NodeSetWriter and

    /// attach it into the given LemonWriter. If the \c _forceIdMap

    /// parameter is true then the writer will write own id map when

    /// the user does not give "id" named map.

    NodeSetWriter(LemonWriter& _writer, const Graph& _graph, 

		  const std::string& _id = std::string(), 

		  bool _forceIdMap = true) 

      : Parent(_writer), idMap(0), forceIdMap(_forceIdMap), 

	graph(_graph), id(_id) {}

    /// \brief Destructor.

    ///

    /// Destructor for NodeSetWriter.

    virtual ~NodeSetWriter() {

      typename MapWriters::iterator it;

      for (it = writers.begin(); it != writers.end(); ++it) {

	delete it->second;

      }

    }

  private:

    NodeSetWriter(const NodeSetWriter&);

    void operator=(const NodeSetWriter&);

  public:

    /// \brief Add a new node map writer command for the writer.

    ///

    /// Add a new node map writer command for the writer.

    template <typename Map>

    NodeSetWriter& writeNodeMap(std::string name, const Map& map) {

      return writeNodeMap<typename Traits::

	template Writer<typename Map::Value>, Map>(name, map);

    }

    /// \brief Add a new node map writer command for the writer.

    ///

    /// Add a new node map writer command for the writer.

    template <typename Writer, typename Map>

    NodeSetWriter& writeNodeMap(std::string name, const Map& map, 

			    const Writer& writer = Writer()) {

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

      checkConcept<_writer_bits::ItemWriter<typename Map::Value>, Writer>();

      writers.push_back(

	make_pair(name, new MapWriter<Node, Map, Writer>(map, writer)));

      return *this;

    }

  protected:

    /// \brief The header of the section.

    ///

    /// It gives back the header of the section.

    virtual std::string header() {

      return "@nodeset " + id;

    }

    /// \brief  Writer function of the section.

    ///

    /// Write the content of the section.

    virtual void write(std::ostream& os) {

      for (int i = 0; i < (int)writers.size(); ++i) {

	if (writers[i].first == "id") {

	  idMap = writers[i].second;

	  forceIdMap = false;

	  break;

	}

      }

      if (forceIdMap) {

	os << "id\t";

      }

      for (int i = 0; i < (int)writers.size(); ++i) {

	os << writers[i].first << '\t';

      }

      os << std::endl;

      for (typename Graph::NodeIt it(graph); it != INVALID; ++it) {

	if (forceIdMap) {

	  os << graph.id(it) << '\t';

	}

	for (int i = 0; i < (int)writers.size(); ++i) {

	  writers[i].second->write(os, it);

	  os << '\t';

	}

	os << std::endl;

      }

    }

  public:

    /// \brief Returns true if the nodeset can write the ids of the nodes.

    ///

    /// Returns true if the nodeset can write the ids of the nodes.

    /// It is possible only if an "id" named map was written or the 

    /// \c _forceIdMap constructor parameter was true.

    bool isIdWriter() const {

      return idMap != 0 || forceIdMap;

    }

    /// \brief Write the id of the given node.

    ///

    /// It writes the id of the given node. If there was written an "id"

    /// named map then it will write the map value belongs to the node.

    /// Otherwise if the \c forceId parameter was true it will write

    /// its id in the graph. 

    void writeId(std::ostream& os, const Node& item) const {

      if (forceIdMap) {

	os << graph.id(item);

      } else {

	idMap->write(os, item);

      }

    }

  private:

    typedef std::vector<std::pair<std::string, WriterBase<Node>*> > MapWriters;

    MapWriters writers;

    WriterBase<Node>* idMap;

    bool forceIdMap;

    typename SmartConstReference<Graph>::Type graph;   

    std::string id;

  };

  /// \ingroup io_group

  /// \brief SectionWriter for writing a graph's edgesets.

  ///

  /// The lemon format can store multiple graph edgesets with several maps. 

  /// The edgeset section's header line is \c \@edgeset \c edgeset_id, but the

  /// \c edgeset_id may be empty.

  ///

  /// The first line of the section contains the names of the maps separated

  /// with white spaces. Each next lines describes a edge in the edgeset. The

  /// line contains the source and the target nodes' id and the mapped 

  /// values for each map.

  ///

  /// If the edgeset contains an \c "id" named map then it will be regarded

  /// as id map. This map should contain only unique values and when the 

  /// \c writeId() member will be called with an edge it will write it's id.

  /// Otherwise if the \c _forceIdMap constructor parameter is true then

  /// the id map will be the id in the graph.

  ///

  /// The edgeset writer needs a node id writer to identify which nodes

  /// have to be connected. If a NodeSetWriter can write the nodes' id,

  /// it will be able to use with this class.

  ///

  /// \relates LemonWriter

  template <typename _Graph, typename _Traits = DefaultWriterTraits>

  class EdgeSetWriter : public CommonSectionWriterBase {

    typedef CommonSectionWriterBase Parent;

  public:

    typedef _Graph Graph;

    typedef _Traits Traits;

    typedef typename Graph::Node Node;

    typedef typename Graph::Edge Edge;

    /// \brief Constructor.

    ///

    /// Constructor for EdgeSetWriter. It creates the EdgeSetWriter and

    /// attach it into the given LemonWriter. It will write node ids by

    /// the \c _nodeIdWriter. If the \c _forceIdMap parameter is true 

    /// then the writer will write own id map if the user does not give 

    /// "id" named map.

    template <typename NodeIdWriter>

    EdgeSetWriter(LemonWriter& _writer, const Graph& _graph, 

		  const NodeIdWriter& _nodeIdWriter, 

		  const std::string& _id = std::string(),

		  bool _forceIdMap = true)

      : Parent(_writer), idMap(0), forceIdMap(_forceIdMap),

	graph(_graph), id(_id) {

      checkConcept<_writer_bits::ItemIdWriter<Node>, NodeIdWriter>();

      nodeIdWriter.reset(new IdWriter<Node, NodeIdWriter>(_nodeIdWriter));

    } 

    /// \brief Destructor.

    ///

    /// Destructor for EdgeSetWriter.

    virtual ~EdgeSetWriter() {

      typename MapWriters::iterator it;

      for (it = writers.begin(); it != writers.end(); ++it) {

	delete it->second;

      }

    }

  private:

    EdgeSetWriter(const EdgeSetWriter&);

    void operator=(const EdgeSetWriter&);

  public:

    /// \brief Add a new edge map writer command for the writer.

    ///

    /// Add a new edge map writer command for the writer.

    template <typename Map>

    EdgeSetWriter& writeEdgeMap(std::string name, const Map& map) {

      return writeEdgeMap<typename Traits::

	template Writer<typename Map::Value>, Map>(name, map);

    }

    /// \brief Add a new edge map writer command for the writer.

    ///

    /// Add a new edge map writer command for the writer.

    template <typename Writer, typename Map>

    EdgeSetWriter& writeEdgeMap(std::string name, const Map& map, 

			    const Writer& writer = Writer()) {

      checkConcept<concept::ReadMap<Edge, typename Map::Value>, Map>();

      checkConcept<_writer_bits::ItemWriter<typename Map::Value>, Writer>();

      writers.push_back(

	make_pair(name, new MapWriter<Edge, Map, Writer>(map, writer)));

      return *this;

    }

  protected:

    /// \brief The header of the section.

    ///

    /// It gives back the header of the section.

    virtual std::string header() {

      return "@edgeset " + id;

    }

    /// \brief  Writer function of the section.

    ///

    /// Write the content of the section.

    virtual void write(std::ostream& os) {

      if (!nodeIdWriter->isIdWriter()) {

	throw DataFormatError("Cannot find nodeset or ID map");

      }

      for (int i = 0; i < (int)writers.size(); ++i) {

	if (writers[i].first == "id") {

	  idMap = writers[i].second;

	  forceIdMap = false;

	  break;

	}

      }

      os << "\t\t";

      if (forceIdMap) {

	os << "id\t";

      }

      for (int i = 0; i < (int)writers.size(); ++i) {

	os << writers[i].first << '\t';

      }

      os << std::endl;

      for (typename Graph::EdgeIt it(graph); it != INVALID; ++it) {

	nodeIdWriter->write(os, graph.source(it));

	os << '\t';

	nodeIdWriter->write(os, graph.target(it));

	os << '\t';

	if (forceIdMap) {

	  os << graph.id(it) << '\t';

	}

	for (int i = 0; i < (int)writers.size(); ++i) {

	  writers[i].second->write(os, it);

	  os << '\t';

	}

	os << std::endl;

      }

    }

  public:

    /// \brief Returns true if the edgeset can write the ids of the edges.

    ///

    /// Returns true if the edgeset can write the ids of the edges.

    /// It is possible only if an "id" named map was written or the 

    /// \c _forceIdMap constructor parameter was true.

    bool isIdWriter() const {

      return forceIdMap || idMap != 0;

    }

    /// \brief Write the id of the given edge.

    ///

    /// It writes the id of the given edge. If there was written an "id"

    /// named map then it will write the map value belongs to the edge.

    /// Otherwise if the \c forceId parameter was true it will write

    /// its id in the graph. 

    void writeId(std::ostream& os, const Edge& item) const {

      if (forceIdMap) {

	os << graph.id(item);

      } else {

	idMap->write(os, item);

      }

    } 

  private:

    typedef std::vector<std::pair<std::string, WriterBase<Edge>*> > MapWriters;

    MapWriters writers;

    WriterBase<Edge>* idMap;

    bool forceIdMap;

    typename SmartConstReference<Graph>::Type graph;   

    std::string id;

    std::auto_ptr<IdWriterBase<Node> > nodeIdWriter;

  };

  /// \ingroup io_group

  /// \brief SectionWriter for writing a undirected edgeset.

  ///

  /// The lemon format can store multiple undirected edgesets with several 

  /// maps. The undirected edgeset section's header line is \c \@undiredgeset 

  /// \c undiredgeset_id, but the \c undiredgeset_id may be empty.

  ///

  /// The first line of the section contains the names of the maps separated

  /// with white spaces. Each next lines describes an undirected edge in the 

  /// edgeset. The line contains the two connected nodes' id and the mapped 

  /// values for each undirected map.

  ///

  /// The section can handle the directed as a syntactical sugar. Two

  /// undirected edge map describes one directed edge map. This two maps

  /// are the forward map and the backward map and the names of this map

  /// is near the same just with a prefix \c '+' or \c '-' character 

  /// difference.

  ///

  /// If the edgeset contains an \c "id" named map then it will be regarded

  /// as id map. This map should contain only unique values and when the 

  /// \c writeId() member will be called with an undirected edge it will 

  /// write it's id. Otherwise if the \c _forceIdMap constructor parameter

  /// is true then the id map will be the id in the graph.

  ///

  /// The undirected edgeset writer needs a node id writer to identify 

  /// which nodes have to be connected. If a NodeSetWriter can write the 

  /// nodes' id, it will be able to use with this class.

  ///

  /// \relates LemonWriter

  template <typename _Graph, typename _Traits = DefaultWriterTraits>

  class UndirEdgeSetWriter : public CommonSectionWriterBase {

    typedef CommonSectionWriterBase Parent;

  public:

    typedef _Graph Graph;

    typedef _Traits Traits;

    typedef typename Graph::Node Node;

    typedef typename Graph::Edge Edge;

    typedef typename Graph::UndirEdge UndirEdge;

    /// \brief Constructor.

    ///

    /// Constructor for UndirEdgeSetWriter. It creates the UndirEdgeSetWriter

    /// and attach it into the given LemonWriter. It will write node ids by

    /// the \c _nodeIdWriter. If the \c _forceIdMap parameter is true 

    /// then the writer will write own id map if the user does not give 

    /// "id" named map.

    template <typename NodeIdWriter>

    UndirEdgeSetWriter(LemonWriter& _writer, const Graph& _graph, 

		       const NodeIdWriter& _nodeIdWriter, 

		       const std::string& _id = std::string(),

		       bool _forceIdMap = true)

      : Parent(_writer), idMap(0), forceIdMap(_forceIdMap),

	graph(_graph), id(_id) {

      checkConcept<_writer_bits::ItemIdWriter<Node>, NodeIdWriter>();

      nodeIdWriter.reset(new IdWriter<Node, NodeIdWriter>(_nodeIdWriter));

    } 

    /// \brief Destructor.

    ///

    /// Destructor for UndirEdgeSetWriter.

    virtual ~UndirEdgeSetWriter() {

      typename MapWriters::iterator it;

      for (it = writers.begin(); it != writers.end(); ++it) {

	delete it->second;

      }

    }

  private:

    UndirEdgeSetWriter(const UndirEdgeSetWriter&);

    void operator=(const UndirEdgeSetWriter&);

  public:

    /// \brief Add a new undirected edge map writer command for the writer.

    ///

    /// Add a new undirected map writer command for the writer.

    template <typename Map>

    UndirEdgeSetWriter& writeUndirEdgeMap(std::string name, const Map& map) {

      return writeUndirEdgeMap<typename Traits::

	template Writer<typename Map::Value>, Map>(name, map);

    }

    /// \brief Add a new undirected map writer command for the writer.

    ///

    /// Add a new undirected map writer command for the writer.

    template <typename Writer, typename Map>

    UndirEdgeSetWriter& writeUndirEdgeMap(std::string name, const Map& map, 

					  const Writer& writer = Writer()) {

      checkConcept<concept::ReadMap<UndirEdge, typename Map::Value>, Map>();

      checkConcept<_writer_bits::ItemWriter<typename Map::Value>, Writer>();

      writers.push_back(

	make_pair(name, new MapWriter<UndirEdge, Map, Writer>(map, writer)));

      return *this;

    }

    /// \brief Add a new directed edge map writer command for the writer.

    ///

    /// Add a new directed map writer command for the writer.

    template <typename Map>

    UndirEdgeSetWriter& writeEdgeMap(std::string name, const Map& map) {

      return writeEdgeMap<typename Traits::

	template Writer<typename Map::Value>, Map>(name, map);

    }

    /// \brief Add a new directed map writer command for the writer.

    ///

    /// Add a new directed map writer command for the writer.

    template <typename Writer, typename Map>

    UndirEdgeSetWriter& writeEdgeMap(std::string name, const Map& map, 

				     const Writer& writer = Writer()) {

      checkConcept<concept::ReadMap<Edge, typename Map::Value>, Map>();

      checkConcept<_writer_bits::ItemWriter<typename Map::Value>, Writer>();

      writeUndirEdge("+" + name, composeMap(forwardMap(graph), map), writer);

      writeUndirEdge("-" + name, composeMap(backwardMap(graph), map), writer);

      return *this;

    }

  protected:

    /// \brief The header of the section.

    ///

    /// It gives back the header of the section.

    virtual std::string header() {

      return "@undiredgeset " + id;

    }

    /// \brief  Writer function of the section.

    ///

    /// Write the content of the section.

    virtual void write(std::ostream& os) {

      if (!nodeIdWriter->isIdWriter()) {

	throw DataFormatError("Cannot find nodeset or ID map");

      }

      for (int i = 0; i < (int)writers.size(); ++i) {

	if (writers[i].first == "id") {

	  idMap = writers[i].second;

	  forceIdMap = false;

	  break;

	}

      }

      os << "\t\t";

      if (forceIdMap) {

	os << "id\t";

      }

      for (int i = 0; i < (int)writers.size(); ++i) {

	os << writers[i].first << '\t';

      }

      os << std::endl;

      for (typename Graph::UndirEdgeIt it(graph); it != INVALID; ++it) {

	nodeIdWriter->write(os, graph.source(it));

	os << '\t';

	nodeIdWriter->write(os, graph.target(it));

	os << '\t';

	if (forceIdMap) {

	  os << graph.id(it) << '\t';

	}

	for (int i = 0; i < (int)writers.size(); ++i) {

	  writers[i].second->write(os, it);

	  os << '\t';

	}

	os << std::endl;

      }

    }

  public:

    /// \brief Returns true if the undirected edgeset can write the ids of 

    /// the edges.

    ///

    /// Returns true if the undirected edgeset can write the ids of the 

    /// undirected edges. It is possible only if an "id" named map was 

    /// written or the \c _forceIdMap constructor parameter was true.

    bool isIdWriter() const {

      return forceIdMap || idMap != 0;

    }

    /// \brief Write the id of the given undirected edge.

    ///

    /// It writes the id of the given undirected edge. If there was written 

    /// an "id" named map then it will write the map value belongs to the 

    /// undirected edge. Otherwise if the \c forceId parameter was true it 

    /// will write its id in the graph. 

    void writeId(std::ostream& os, const UndirEdge& item) const {

      if (forceIdMap) {

	os << graph.id(item);

      } else {

	idMap->write(os, item);

      }

    } 

    /// \brief Write the id of the given edge.

    ///

    /// It writes the id of the given edge. If there was written 

    /// an "id" named map then it will write the map value belongs to the 

    /// edge. Otherwise if the \c forceId parameter was true it 

    /// will write its id in the graph. If the edge is forward map

    /// then its prefix character is \c '+' elsewhere \c '-'.

    void writeId(std::ostream& os, const Edge& item) const {

      if (graph.forward(item)) {

	os << "+ ";

      } else {

	os << "- ";

      }

      if (forceIdMap) {

	os << graph.id(item);

      } else {

	idMap->write(os, item);

      }

    } 

  private:

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

				  WriterBase<UndirEdge>*> > MapWriters;

    MapWriters writers;

    WriterBase<UndirEdge>* idMap;

    bool forceIdMap;

    typename SmartConstReference<Graph>::Type graph;   

    std::string id;

    std::auto_ptr<IdWriterBase<Node> > nodeIdWriter;

  };

  /// \ingroup io_group

  /// \brief SectionWriter for writing labeled nodes.

  ///

  /// The nodes section's header line is \c \@nodes \c nodes_id, but the

  /// \c nodes_id may be empty.

  ///

  /// Each line in the section contains the label of the node and 

  /// then the node id. 

  ///

  /// \relates LemonWriter

  template <typename _Graph>

  class NodeWriter : public CommonSectionWriterBase {

    typedef CommonSectionWriterBase Parent;

    typedef _Graph Graph;

    typedef typename Graph::Node Node;

  public:

    /// \brief Constructor.

    ///

    /// Constructor for NodeWriter. It creates the NodeWriter and

    /// attach it into the given LemonWriter. The given \c _IdWriter

    /// will write the nodes' id what can be a nodeset writer.

    template <typename _IdWriter>

    NodeWriter(LemonWriter& _writer, const _IdWriter& _idWriter, 

	       const std::string& _id = std::string()) 

      : Parent(_writer), id(_id) {

      checkConcept<_writer_bits::ItemIdWriter<Node>, _IdWriter>();

      idWriter.reset(new IdWriter<Node, _IdWriter>(_idWriter));

    }

    /// \brief Destructor.

    ///

    /// Destructor for NodeWriter.

    virtual ~NodeWriter() {}

  private:

    NodeWriter(const NodeWriter&);

    void operator=(const NodeWriter&);

  public:

    /// \brief Add a node writer command for the NodeWriter.

    ///

    /// Add a node writer command for the NodeWriter.

    void writeNode(const std::string& name, const Node& item) {

      writers.push_back(make_pair(name, &item));

    }

  protected:

    /// \brief Header checking function.

    ///

    /// It gives back true when the header line start with \c \@nodes,

    /// and the header line's id and the writer's id are the same.

    virtual std::string header() {

      return "@nodes " + id;

    }

    /// \brief  Writer function of the section.

    ///

    /// Write the content of the section.

    virtual void write(std::ostream& os) {

      if (!idWriter->isIdWriter()) {

	throw DataFormatError("Cannot find nodeset or ID map");

      }

      for (int i = 0; i < (int)writers.size(); ++i) {

	os << writers[i].first << ' ';

	idWriter->write(os, *(writers[i].second));

	os << std::endl;

      }

    }

  private:

    std::string id;

    typedef std::vector<std::pair<std::string, const Node*> > NodeWriters;

    NodeWriters writers;

    std::auto_ptr<IdWriterBase<Node> > idWriter;

  };

  /// \ingroup io_group

  /// \brief SectionWriter for writing labeled edges.

  ///

  /// The edges section's header line is \c \@edges \c edges_id, but the

  /// \c edges_id may be empty.

  ///

  /// Each line in the section contains the label of the edge and 

  /// then the edge id. 

  ///

  /// \relates LemonWriter

  template <typename _Graph>

  class EdgeWriter : public CommonSectionWriterBase {

    typedef CommonSectionWriterBase Parent;

    typedef _Graph Graph;

    typedef typename Graph::Edge Edge;

  public:

    /// \brief Constructor.

    ///

    /// Constructor for EdgeWriter. It creates the EdgeWriter and

    /// attach it into the given LemonWriter. The given \c _IdWriter

    /// will write the edges' id what can be a edgeset writer.

    template <typename _IdWriter>

    EdgeWriter(LemonWriter& _writer, const _IdWriter& _idWriter, 

	       const std::string& _id = std::string()) 

      : Parent(_writer), id(_id) {

      checkConcept<_writer_bits::ItemIdWriter<Edge>, _IdWriter>();

      idWriter.reset(new IdWriter<Edge, _IdWriter>(_idWriter));

    }

    /// \brief Destructor.

    ///

    /// Destructor for EdgeWriter.

    virtual ~EdgeWriter() {}

  private:

    EdgeWriter(const EdgeWriter&);

    void operator=(const EdgeWriter&);

  public:

    /// \brief Add an edge writer command for the EdgeWriter.

    ///

    /// Add an edge writer command for the EdgeWriter.

    void writeEdge(const std::string& name, const Edge& item) {

      writers.push_back(make_pair(name, &item));

    }

  protected:

    /// \brief Header checking function.