/* -*- mode: C++; indent-tabs-mode: nil; -*-

 *

 * 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.

 *

 */

#ifndef LEMON_BITS_ALTERATION_NOTIFIER_H

#define LEMON_BITS_ALTERATION_NOTIFIER_H

#include <vector>

#include <list>

#include <lemon/core.h>

//\ingroup graphbits

//\file

//\brief Observer notifier for graph alteration observers.

namespace lemon {

  // \ingroup graphbits

  //

  // \brief Notifier class to notify observes about alterations in

  // a container.

  //

  // The simple graphs can be refered as two containers: a node container

  // and an edge container. But they do not store values directly, they

  // are just key continars for more value containers, which are the

  // node and edge maps.

  //

  // The node and edge sets of the graphs can be changed as we add or erase

  // nodes and edges in the graph. LEMON would like to handle easily

  // that the node and edge maps should contain values for all nodes or

  // edges. If we want to check on every indicing if the map contains

  // the current indicing key that cause a drawback in the performance

  // in the library. We use another solution: we notify all maps about

  // an alteration in the graph, which cause only drawback on the

  // alteration of the graph.

  //

  // This class provides an interface to a node or edge container.

  // The first() and next() member functions make possible

  // to iterate on the keys of the container.

  // The id() function returns an integer id for each key.

  // The maxId() function gives back an upper bound of the ids.

  //

  // For the proper functonality of this class, we should notify it

  // about each alteration in the container. The alterations have four type:

  // add(), erase(), build() and clear(). The add() and

  // erase() signal that only one or few items added or erased to or

  // from the graph. If all items are erased from the graph or if a new graph

  // is built from an empty graph, then it can be signaled with the

  // clear() and build() members. Important rule that if we erase items

  // from graphs we should first signal the alteration and after that erase

  // them from the container, on the other way on item addition we should

  // first extend the container and just after that signal the alteration.

  //

  // The alteration can be observed with a class inherited from the

  // ObserverBase nested class. The signals can be handled with

  // overriding the virtual functions defined in the base class.  The

  // observer base can be attached to the notifier with the

  // attach() member and can be detached with detach() function. The

  // alteration handlers should not call any function which signals

  // an other alteration in the same notifier and should not

  // detach any observer from the notifier.

  //

  // Alteration observers try to be exception safe. If an add() or

  // a clear() function throws an exception then the remaining

  // observeres will not be notified and the fulfilled additions will

  // be rolled back by calling the erase() or clear() functions.

  // Hence erase() and clear() should not throw exception.

  // Actullay, they can throw only \ref ImmediateDetach exception,

  // which detach the observer from the notifier.

  //

  // There are some cases, when the alteration observing is not completly

  // reliable. If we want to carry out the node degree in the graph

  // as in the \ref InDegMap and we use the reverseArc(), then it cause

  // unreliable functionality. Because the alteration observing signals

  // only erasing and adding but not the reversing, it will stores bad

  // degrees. Apart form that the subgraph adaptors cannot even signal

  // the alterations because just a setting in the filter map can modify

  // the graph and this cannot be watched in any way.

  //

  // \param _Container The container which is observed.

  // \param _Item The item type which is obserbved.

  template <typename _Container, typename _Item>

  class AlterationNotifier {

  public:

    typedef True Notifier;

    typedef _Container Container;

    typedef _Item Item;

    // \brief Exception which can be called from clear() and

    // erase().

    //

    // From the clear() and erase() function only this

    // exception is allowed to throw. The exception immediatly

    // detaches the current observer from the notifier. Because the

    // clear() and erase() should not throw other exceptions

    // it can be used to invalidate the observer.

    struct ImmediateDetach {};

    // \brief ObserverBase is the base class for the observers.

    //

    // ObserverBase is the abstract base class for the observers.

    // It will be notified about an item was inserted into or

    // erased from the graph.

    //

    // The observer interface contains some pure virtual functions

    // to override. The add() and erase() functions are

    // to notify the oberver when one item is added or erased.

    //

    // The build() and clear() members are to notify the observer

    // about the container is built from an empty container or

    // is cleared to an empty container.

    class ObserverBase {

    protected:

      typedef AlterationNotifier Notifier;

      friend class AlterationNotifier;

      // \brief Default constructor.

      //

      // Default constructor for ObserverBase.

      ObserverBase() : _notifier(0) {}

      // \brief Constructor which attach the observer into notifier.

      //

      // Constructor which attach the observer into notifier.

      ObserverBase(AlterationNotifier& nf) {

        attach(nf);

      }

      // \brief Constructor which attach the obserever to the same notifier.

      //

      // Constructor which attach the obserever to the same notifier as

      // the other observer is attached to.

      ObserverBase(const ObserverBase& copy) {

        if (copy.attached()) {

          attach(*copy.notifier());

        }

      }

      // \brief Destructor

      virtual ~ObserverBase() {

        if (attached()) {

          detach();

        }

      }

      // \brief Attaches the observer into an AlterationNotifier.

      //

      // This member attaches the observer into an AlterationNotifier.

      void attach(AlterationNotifier& nf) {

        nf.attach(*this);

      }

      // \brief Detaches the observer into an AlterationNotifier.

      //

      // This member detaches the observer from an AlterationNotifier.

      void detach() {

        _notifier->detach(*this);

      }

      // \brief Gives back a pointer to the notifier which the map

      // attached into.

      //

      // This function gives back a pointer to the notifier which the map

      // attached into.

      Notifier* notifier() const { return const_cast<Notifier*>(_notifier); }

      // Gives back true when the observer is attached into a notifier.

      bool attached() const { return _notifier != 0; }

    private:

      ObserverBase& operator=(const ObserverBase& copy);

    protected:

      Notifier* _notifier;

      typename std::list<ObserverBase*>::iterator _index;

      // \brief The member function to notificate the observer about an

      // item is added to the container.

      //

      // The add() member function notificates the observer about an item

      // is added to the container. It have to be overrided in the

      // subclasses.

      virtual void add(const Item&) = 0;

      // \brief The member function to notificate the observer about

      // more item is added to the container.

      //

      // The add() member function notificates the observer about more item

      // is added to the container. It have to be overrided in the

      // subclasses.

      virtual void add(const std::vector<Item>& items) = 0;

      // \brief The member function to notificate the observer about an

      // item is erased from the container.

      //

      // The erase() member function notificates the observer about an

      // item is erased from the container. It have to be overrided in

      // the subclasses.

      virtual void erase(const Item&) = 0;

      // \brief The member function to notificate the observer about

      // more item is erased from the container.

      //

      // The erase() member function notificates the observer about more item

      // is erased from the container. It have to be overrided in the

      // subclasses.

      virtual void erase(const std::vector<Item>& items) = 0;

      // \brief The member function to notificate the observer about the

      // container is built.

      //

      // The build() member function notificates the observer about the

      // container is built from an empty container. It have to be

      // overrided in the subclasses.

      virtual void build() = 0;

      // \brief The member function to notificate the observer about all

      // items are erased from the container.

      //

      // The clear() member function notificates the observer about all

      // items are erased from the container. It have to be overrided in

      // the subclasses.

      virtual void clear() = 0;

    };

  protected:

    const Container* container;

    typedef std::list<ObserverBase*> Observers;

    Observers _observers;

  public:

    // \brief Default constructor.

    //

    // The default constructor of the AlterationNotifier.

    // It creates an empty notifier.

    AlterationNotifier()

      : container(0) {}

    // \brief Constructor.

    //

    // Constructor with the observed container parameter.

    AlterationNotifier(const Container& _container)

      : container(&_container) {}

    // \brief Copy Constructor of the AlterationNotifier.

    //

    // Copy constructor of the AlterationNotifier.

    // It creates only an empty notifier because the copiable

    // notifier's observers have to be registered still into that notifier.

    AlterationNotifier(const AlterationNotifier& _notifier)

      : container(_notifier.container) {}

    // \brief Destructor.

    //

    // Destructor of the AlterationNotifier.

    ~AlterationNotifier() {

      typename Observers::iterator it;

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

        (*it)->_notifier = 0;

      }

    }

    // \brief Sets the container.

    //

    // Sets the container.

    void setContainer(const Container& _container) {

      container = &_container;

    }

  protected:

    AlterationNotifier& operator=(const AlterationNotifier&);

  public:

    // \brief First item in the container.

    //

    // Returns the first item in the container. It is

    // for start the iteration on the container.

    void first(Item& item) const {

      container->first(item);

    }

    // \brief Next item in the container.

    //

    // Returns the next item in the container. It is

    // for iterate on the container.

    void next(Item& item) const {

      container->next(item);

    }

    // \brief Returns the id of the item.

    //

    // Returns the id of the item provided by the container.

    int id(const Item& item) const {

      return container->id(item);

    }

    // \brief Returns the maximum id of the container.

    //

    // Returns the maximum id of the container.

    int maxId() const {

      return container->maxId(Item());

    }

  protected:

    void attach(ObserverBase& observer) {

      observer._index = _observers.insert(_observers.begin(), &observer);

      observer._notifier = this;

    }

    void detach(ObserverBase& observer) {

      _observers.erase(observer._index);

      observer._index = _observers.end();

      observer._notifier = 0;

    }

  public:

    // \brief Notifies all the registed observers about an item added to

    // the container.

    //

    // It notifies all the registed observers about an item added to

    // the container.

    void add(const Item& item) {

      typename Observers::reverse_iterator it;

      try {

        for (it = _observers.rbegin(); it != _observers.rend(); ++it) {

          (*it)->add(item);

        }

      } catch (...) {

        typename Observers::iterator jt;

        for (jt = it.base(); jt != _observers.end(); ++jt) {

          (*jt)->erase(item);

        }

        throw;

      }

    }

    // \brief Notifies all the registed observers about more item added to

    // the container.

    //

    // It notifies all the registed observers about more item added to

    // the container.

    void add(const std::vector<Item>& items) {

      typename Observers::reverse_iterator it;

      try {

        for (it = _observers.rbegin(); it != _observers.rend(); ++it) {

          (*it)->add(items);

        }

      } catch (...) {

        typename Observers::iterator jt;

        for (jt = it.base(); jt != _observers.end(); ++jt) {

          (*jt)->erase(items);

        }

        throw;

      }

    }

    // \brief Notifies all the registed observers about an item erased from

    // the container.

    //

    // It notifies all the registed observers about an item erased from

    // the container.

    void erase(const Item& item) throw() {

      typename Observers::iterator it = _observers.begin();

      while (it != _observers.end()) {

        try {

          (*it)->erase(item);

          ++it;

        } catch (const ImmediateDetach&) {

          (*it)->_index = _observers.end();

          (*it)->_notifier = 0;

          it = _observers.erase(it);

        }

      }

    }

    // \brief Notifies all the registed observers about more item erased

    // from the container.

    //

    // It notifies all the registed observers about more item erased from

    // the container.

    void erase(const std::vector<Item>& items) {

      typename Observers::iterator it = _observers.begin();

      while (it != _observers.end()) {

        try {

          (*it)->erase(items);

          ++it;

        } catch (const ImmediateDetach&) {

          (*it)->_index = _observers.end();

          (*it)->_notifier = 0;

          it = _observers.erase(it);

        }

      }

    }

    // \brief Notifies all the registed observers about the container is

    // built.

    //

    // Notifies all the registed observers about the container is built

    // from an empty container.

    void build() {

      typename Observers::reverse_iterator it;

      try {

        for (it = _observers.rbegin(); it != _observers.rend(); ++it) {

          (*it)->build();

        }

      } catch (...) {

        typename Observers::iterator jt;

        for (jt = it.base(); jt != _observers.end(); ++jt) {

          (*jt)->clear();

        }

        throw;

      }

    }

    // \brief Notifies all the registed observers about all items are

    // erased.

    //

    // Notifies all the registed observers about all items are erased

    // from the container.

    void clear() {

      typename Observers::iterator it = _observers.begin();

      while (it != _observers.end()) {

        try {

          (*it)->clear();

          ++it;

        } catch (const ImmediateDetach&) {

          (*it)->_index = _observers.end();

          (*it)->_notifier = 0;

          it = _observers.erase(it);

        }

      }

    }

  };

}

#endif