/*
 * Copyright (c) 1999-2000, Eric Moon.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions, and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions, and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR "AS IS" AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF TITLE, NON-INFRINGEMENT, MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
 * TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */


// IObservable.h
// * PURPOSE
//   Defines a general observable-object interface.
// * HISTORY
//   e.moon             19aug99         Begun

#ifndef __IObservable_H__
#define __IObservable_H__

class BMessenger;

#include "cortex_defs.h"
__BEGIN_CORTEX_NAMESPACE

class IObservable {

public:
        IObservable() { }
        virtual ~IObservable() { }
public:                                                                                 // *** deletion
        // clients must call release() rather than deleting,
        // to ensure that all observers are notified of the
        // object's demise.  if the object has already been
        // released, return an error.
        virtual status_t release()=0;

public:                                                                                 // *** accessors
        // return true if release() has been called, false otherwise.
        virtual bool isReleased() const=0;

protected:                                                                      // *** hooks
        // must be called after an observer has been added (this is a good
        // place to send an acknowledgement)
        virtual void observerAdded(
                const BMessenger&                               observer) {TOUCH(observer);}
                
        // must be called after an observer has been removed
        virtual void observerRemoved(
                const BMessenger&                               observer) {TOUCH(observer);}

        // must be called once all observers have been removed
        virtual void releaseComplete() {}

protected:                                                                      // *** operations
        // call to send the given message to all observers.
        // Responsibility for deletion of the message remains with
        // the caller.
        virtual status_t notify(
                BMessage*                                                               message)=0;

        // must be called by release() if targets remain to be
        // released.  should notify all targets with an appropriate
        // release-notification message (such as M_RELEASE_OBSERVABLE).
        virtual void notifyRelease()=0;
};

__END_CORTEX_NAMESPACE
#endif /*__IObservable_H__*/