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Ahome Tooling NativeTools - GWT high speed native collection, browser access, and JSON utilities.

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/*
   Copyright (c) 2014,2015,2016 Ahome' Innovation Technologies. All rights reserved.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
 */

package com.ait.tooling.nativetools.client.storage;

import java.util.Objects;

import com.ait.tooling.nativetools.client.event.HandlerRegistrationManager;
import com.ait.tooling.nativetools.client.storage.event.SessionStorageEvent;
import com.ait.tooling.nativetools.client.storage.event.SessionStorageHandler;
import com.google.gwt.event.shared.HandlerManager;
import com.google.gwt.event.shared.HandlerRegistration;
import com.google.gwt.storage.client.Storage;
import com.google.gwt.storage.client.StorageEvent;

public final class SessionStorage extends AbstractStorage
{
    private static SessionStorage INSTANCE;

    private HandlerManager        m_events;

    private SessionStorage()
    {
        super(CacheType.SESSION, Storage.getSessionStorageIfSupported());
    }

    public static final SessionStorage get()
    {
        if (null == INSTANCE)
        {
            INSTANCE = new SessionStorage();
        }
        return INSTANCE;
    }

    public final HandlerRegistration addSessionStorageHandler(SessionStorageHandler handler)
    {
        handler = Objects.requireNonNull(handler);

        if (null == m_events)
        {
            m_events = new HandlerManager(this);
        }
        if (isSupported())
        {
            final HandlerRegistration proxy = Storage.addStorageEventHandler(new StorageEvent.Handler()
            {
                @Override
                public void onStorageChange(final StorageEvent event)
                {
                    if (false == isLocalStorage(event))
                    {
                        m_events.fireEvent(new SessionStorageEvent(get(), event.getKey(), event.getOldValue(), event.getNewValue()));
                    }
                }
            });
            return new HandlerRegistrationManager(m_events.addHandler(SessionStorageEvent.TYPE, handler), proxy);
        }
        return m_events.addHandler(SessionStorageEvent.TYPE, handler);
    }
}