/*

* Copyright (c) 2008 Nokia Corporation and/or its subsidiary(-ies).

* All rights reserved.

* This component and the accompanying materials are made available

* under the terms of "Eclipse Public License v1.0"

* which accompanies this distribution, and is available

* at the URL "http://www.eclipse.org/legal/epl-v10.html".

*

* Initial Contributors:

* Nokia Corporation - initial contribution.

*

* Contributors:

*

* Description:

*

*/

package com.nokia.mj.impl.rt.support;

import com.nokia.mj.impl.utils.Uid;

import java.util.Vector;

import java.util.Enumeration;

import java.security.Permission;

import java.security.AccessControlException;

/**

 * ApplicationUtils is an abstract base class for API implementations,

 * which allows them to use miscellanous utilities related to the running

 * application.

 * <p>

 * The class provides a static getter method for getting an instance of

 * the running application. In those runtimes that are always running only

 * one instance (like MIDP) returns always the same instance of the

 * ApplicationUtils. However those runtimes (like eRCP), that may run several

 * application in the same JVM instance, will return an application specific

 * instance.

 * <p>

 * The runtime implementation hides the solving of the correct application

 * when method <code>getInstace</code> is called. However it must be noted

 * that if the call is made some common thread, the <code>getInstace</code>

 * might not able to solve the correct application.

 * <p>

 * Example how to register a shutdown listener.

 * <pre>

 * package com.nokia.mj.impl.mypackage;

 *

 * import com.nokia.mj.impl.rt.support.ApplicationUtils;

 *      public void myClass()

 *      {

 *          public void myMethod()

 *          {

 *              // Get the insatnce of ApplicationUtils.

 *              ApplicationUtils appUtils = ApplicationUtils.getInstance();

 *

 *              // Get the name of the application.

 *              appUtils.addShutdownListener(new ShutdownListener()

 *              {

 *                  public void shuttingDown()

 *                  {

 *                      //Do cleaning...

 *                  }

 *

 *              });

 *

 *

 *              // My implementation...

 *          }

 *      }

 *</pre>

 * @author Nokia Corporation

 * @version 1.0

 */

public abstract class ApplicationUtils

{

    /**

     * Name of the runtime specific class that extends this base class.

     */

    private static final String PORTCLASS = ".ApplicationUtilsImpl";

    /**

     * A singleton instance of runtime dependent instance of class extending

     * the ApplicationUtils base class.

     */

    protected static ApplicationUtils sInstance = null;

    /**

     * A set of listeners who wants to receive notification when the

     * application is abaout to close.

     */

    private Vector mListeners;

    /**

     * A lock for synchronizing the thw start up waiting feature.

     */

    private Object   mApplicationStartLock = new Object();

    /**

     * Information wheteher to continue start up or cancel it.

     */

    private Boolean  mStartCmd;

    /**

     * When this class is first loaded the static initializer will create a

     * singleton instance of runtime dependent instance of class extending the

     * ApplicationUtils base class. The class is created using dynamic

     * instantiation (<code>Class.forname & Class.newInstance</code>) and

     * the name of the class is a combination of PACKAGE_PREFIX +

     * <value of system property PACKAGE_END_PROPERTY_NAME >

     * + .<value of PORTCLASS member variable &gt.

     */

    static

    {

        //Get the system proptery defining the end of package.

        String packageEnd =

            System.getProperty(ApplicationInfo.PACKAGE_END_PROPERTY_NAME);

        if (packageEnd == null)

        {

            throw new RuntimeException

            ("Not able to load " + PORTCLASS + "class since " +

             ApplicationInfo.PACKAGE_END_PROPERTY_NAME +

             " system property is undefined");

        }

        //Construct the class

        String className = ApplicationInfo.PACKAGE_PREFIX +

                           packageEnd + PORTCLASS;

        try

        {

            Class clazz = Class.forName(className);

            sInstance = (ApplicationUtils)clazz.newInstance();

        }

        catch (Exception e)

        {

            e.printStackTrace();

            throw new RuntimeException("Not able to instantiate class " +

                                       className+". Reason is: " + e);

        }

    }

    /**

     * Returns an instace of ApplicationUtils class which provides access to

     * application related runtime services.

     *

     * @return the ApplicationUtils object, null if the construction of the

     *         object has faild

     */

    public static ApplicationUtils getInstance()

    {

        return sInstance;

    }

    /**

     * Notifies the runtime that an exit command has been received and the

     * application is being tried to close nicely. The runtime is responsible

     * for killing the application if it doesn't close itself nicely after

     * specified grace time. The specified grace time is runtime dependent.

     * <p>

     * This method is meant ONLY for the UI and no other API are allowed

     * to use it. The UI must use this API ONLY when the user explicitly

     * wants to close the application using some platform depedent feataure

     * (e.g. red key in S60). If the user tries to close the application

     * using the mechanism provided by the application itself, this method

     * must not be called.

     * <p>

     * This method is a problematic in such runtimes that may run more than one

     * application in same JVM instance (e.g. eRCP). If the application

     * doesn't close nicely the runtime may have to terminate

     * the whole JVM process, which leads closing all the running applications

     * and the runtime itself.

     *

     */

    public abstract void notifyExitCmd();

    /**

     * Determines whether the access request indicated by the specified

     * permission should be allowed or denied, based on the security policy

     * currently in effect. This method quietly returns if the access request

     * is permitted, or throws a suitable AccessControlException otherwise.

     * <p>

     * The design decision was that all the API implementation should use this

     * method for making security checkings and avoid using the

     * <code>checkPermission</code> method <code>AccessController</code> class,

     * which is left for application usage only.

     * <p>

     * The runtime implementation is responsible for forwarding security

     * checking to correct securty handler. In MIDP this would be Midp security

     * component while in 'main' type of application the handler would be the

     * <code>AccessController</code> class.

     *

     * @param p the requested permission.

     * @throws AccessControlException if the specified permission is not

     *         permitted, based on the current security policy.

     * @throws NullPointerException if the specified permission is null.

     */

    public abstract void checkPermission(Permission p)

    throws AccessControlException,

                NullPointerException;

    public abstract void checkPermission(Uid appUid,Permission p)

    throws AccessControlException,

                NullPointerException;

    /**

     * Adds a shutdown notifications listener to receive notifications when

     * the application is about to close.

     * <p>

     * When the runtime receives information that the application is closing

     * (either from the application itself or from the system) the runtime

     * will send a notification to all registered listeners by calling

     * {@link ShutdownListener#shuttingDown() shuttingDown} method. All the

     * calls are made in a loop in one thread, so if some listener blocks the

     * call the rest of the listeners don't get the notification.

     * <p>

     * There can be more than one listener.

     *

     * @param listener the new listener.

     */

    public void addShutdownListener(ShutdownListener listener)

{

        if (mListeners == null)

        {

            mListeners = new Vector();

        }

        mListeners.addElement(listener);

    }

    /**

     * Waits (if needed) until the application to be started is known.

     * This method can be used for pre-warming features. If the runtime is in

     * pre-warmed state where the application to be launched is not yet known,

     * this method will block. It is safe to call this method if the application

     * is already known - in that case the method won't block. Once the

     * application is known all the waiters will be released. Knowing the

     * application doesn't necessarily mean that the application it self

     * has been created (might happen later). The method will provide info

     * whether to continue or cancel the start up as a return value.

     * @return true if the user should continue starting, otherwise the user

     *              should do the required shut down proceures.

     */

    public boolean waitStart()

    {

        synchronized (mApplicationStartLock)

        {

            if (mStartCmd == null)

            {

                try

                {

                    mApplicationStartLock.wait();

                }

                catch (InterruptedException ie)

                {

                }

            }

            return mStartCmd == null ? false : mStartCmd.booleanValue();

        }

    }

    /**

     * Can be used to inform the runtime to pause the running application. The

     * origin could be e.g. flip close or application going to back ground.

     */

    public void pauseApplication()

    {

        // Empty implementation as default.

    }

    /**

     * Can be used to inform the runtime to resume the paused application. The

     * origin could be e.g. flip open or application going to fore ground.

     */

    public void resumeApplication()

    {

        // Empty implementation as default.

    }

    /**

     * Releases the start waiters.

     */

    protected void releaseStartWaiter(boolean doStart)

    {

        if (mApplicationStartLock != null)

        {

            synchronized (mApplicationStartLock)

            {

                mStartCmd = new Boolean(doStart);

                mApplicationStartLock.notifyAll();

            }

        }

    }

    /**

     * Sends shutdown notification to all the registered listeners.

     */

    protected void doShutdown()

    {

        if (mListeners != null)

        {

            Enumeration enumer = mListeners.elements();

            while (enumer.hasMoreElements())

            {

                ShutdownListener listener =

                    (ShutdownListener)enumer.nextElement();

                listener.shuttingDown();

            }

        }

    }

}