/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 *
 * The contents of this file are subject to the Netscape Public License
 * Version 1.0 (the "NPL"); you may not use this file except in
 * compliance with the NPL.  You may obtain a copy of the NPL at
 * http://www.mozilla.org/NPL/
 *
 * Software distributed under the NPL is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the NPL
 * for the specific language governing rights and limitations under the
 * NPL.
 *
 * The Initial Developer of this code under the NPL is Netscape
 * Communications Corporation.  Portions created by Netscape are
 * Copyright (C) 1998 Netscape Communications Corporation.  All Rights
 * Reserved.
 */

#ifndef nsIServiceManager_h___
#define nsIServiceManager_h___

#include "nsRepository.h"

class nsIShutdownListener;

/**
 * The nsIServiceManager manager interface provides a means to obtain
 * global services in an application. The service manager depends on the 
 * repository to find and instantiate factories to obtain services.
 *
 * Users of the service manager must first obtain a pointer to the global
 * service manager by calling NS_GetGlobalServiceManager. After that, 
 * they can request specific services by calling GetService. When they are
 * finished with a service the release it by calling ReleaseService (instead
 * of releasing the service object directly):
 *
 *    nsICacheManager* cm;
 *    nsServiceManager::GetService(kCacheManagerCID, kICacheManagerIID, (nsISupports**)&cm);
 *
 *    ... use cm, and then sometime later ...
 *
 *    nsServiceManager::ReleaseService(kCacheManagerCID, cm);
 *
 * A user of a service may keep references to particular services indefinitely
 * and only must call ReleaseService when it shuts down. However if the user
 * wishes to voluntarily cooperate with the shutdown of the service it is 
 * using, it may supply an nsIShutdownListener to provide for asynchronous
 * release of the services it is using. The shutdown listener's OnShutdown
 * method will be called for a service that is being shut down, and it is
 * its responsiblity to release references obtained from that service if at
 * all possible.
 *
 * The process of shutting down a particular service is initiated by calling
 * the service manager's ShutdownService method. This will iterate through
 * all the registered shutdown listeners for the service being shut down, and
 * then will attempt to unload the library associated with the service if
 * possible. The status result of ShutdownService indicates whether the 
 * service was successfully shut down, failed, or was not in service.
 *
 * XXX QUESTIONS:
 * - Should a "service" be more than nsISupports? Should it be a factory 
 *   and/or have Startup(), Shutdown(), etc.
 * - If the asynchronous OnShutdown operation gets called, does the user
 *   of a service still need to call ReleaseService? (Or should they _not_
 *   call it?)
 */
class nsIServiceManager : public nsISupports {
public:

    NS_IMETHOD
    GetService(const nsCID& aClass, const nsIID& aIID,
               nsISupports* *result,
               nsIShutdownListener* shutdownListener = NULL) = 0;

    NS_IMETHOD
    ReleaseService(const nsCID& aClass, nsISupports* service,
                   nsIShutdownListener* shutdownListener = NULL) = 0;

    /**
     * Requests a service to be shut down, possibly unloading its DLL.
     *
     * @returns NS_OK - if shutdown was successful and service was unloaded,
     * @returns NS_ERROR_SERVICE_NOT_FOUND - if shutdown failed because
     *          the service was not currently loaded
     * @returns NS_ERROR_SERVICE_IN_USE - if shutdown failed because some
     *          user of the service wouldn't voluntarily release it by using
     *          a shutdown listener.
     */
    NS_IMETHOD
    ShutdownService(const nsCID& aClass) = 0;

};

#define NS_ISERVICEMANAGER_IID                       \
{ /* cf0df3b0-3401-11d2-8163-006008119d7a */         \
    0xcf0df3b0,                                      \
    0x3401,                                          \
    0x11d2,                                          \
    {0x81, 0x63, 0x00, 0x60, 0x08, 0x11, 0x9d, 0x7a} \
}

#define NS_ERROR_SERVICE_NOT_FOUND      NS_ERROR_GENERATE_SUCCESS(NS_ERROR_MODULE_XPCOM, 22)
#define NS_ERROR_SERVICE_IN_USE         NS_ERROR_GENERATE_SUCCESS(NS_ERROR_MODULE_XPCOM, 23)

////////////////////////////////////////////////////////////////////////////////

class nsIShutdownListener : public nsISupports {
public:

    NS_IMETHOD
    OnShutdown(const nsCID& aClass, nsISupports* service) = 0;

};

#define NS_ISHUTDOWNLISTENER_IID                     \
{ /* 56decae0-3406-11d2-8163-006008119d7a */         \
    0x56decae0,                                      \
    0x3406,                                          \
    0x11d2,                                          \
    {0x81, 0x63, 0x00, 0x60, 0x08, 0x11, 0x9d, 0x7a} \
}

////////////////////////////////////////////////////////////////////////////////
// Interface to Global Services

class NS_COM nsServiceManager {
public:
    static nsresult GetService(const nsCID& aClass, const nsIID& aIID,
                               nsISupports* *result,
                               nsIShutdownListener* shutdownListener = NULL);

    static nsresult ReleaseService(const nsCID& aClass, nsISupports* service,
                                   nsIShutdownListener* shutdownListener = NULL);

    static nsresult ShutdownService(const nsCID& aClass);

    // Since the global Service Manager is truly global, there's no need to
    // release it.
    static nsresult GetGlobalServiceManager(nsIServiceManager* *result);

protected:
    static nsIServiceManager* globalServiceManager;

};

////////////////////////////////////////////////////////////////////////////////

#endif /* nsIServiceManager_h___ */