/*******************************************************************************
 * Copyright (c) 2005, 2007 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *     Brad Reynolds - bug 164653
 *******************************************************************************/
module org.eclipse.core.databinding.observable.value.AbstractVetoableValue;

import java.lang.all;

import org.eclipse.core.databinding.observable.Diffs;
import org.eclipse.core.databinding.observable.Realm;
import org.eclipse.core.internal.databinding.Util;

/**
 * 
 * <p>
 * This class is thread safe. All state accessing methods must be invoked from
 * the {@link Realm#isCurrent() current realm}. Methods for adding and removing
 * listeners may be invoked from any thread.
 * </p>
 * @since 1.0
 * 
 */
public abstract class AbstractVetoableValue : AbstractObservableValue
        , IVetoableValue {

    /**
     * Creates a new vetoable value.
     */
    public this() {
        this(Realm.getDefault());
    }

    /**
     * @param realm
     */
    public this(Realm realm) {
        super(realm);
    }

    final protected void doSetValue(Object value) {
        Object currentValue = doGetValue();
        ValueDiff diff = Diffs.createValueDiff(currentValue, value);
        bool okToProceed = fireValueChanging(diff);
        if (!okToProceed) {
            throw new ChangeVetoException("Change not permitted"); //$NON-NLS-1$
        }
        doSetApprovedValue(value);
        
        if (!Util.equals(diff.getOldValue(), diff.getNewValue())) {
            fireValueChange(diff);
        }
    }

    /**
     * Sets the value. Invoked after performing veto checks.  Should not fire change events.
     * 
     * @param value
     */
    protected abstract void doSetApprovedValue(Object value);

    public synchronized void addValueChangingListener(
            IValueChangingListener listener) {
        addListener(ValueChangingEvent.TYPE, listener);
    }

    public synchronized void removeValueChangingListener(
            IValueChangingListener listener) {
        removeListener(ValueChangingEvent.TYPE, listener);
    }

    /**
     * Notifies listeners about a pending change, and returns true if no
     * listener vetoed the change.
     * 
     * @param diff
     * @return false if the change was vetoed, true otherwise
     */
    protected bool fireValueChanging(ValueDiff diff) {
        checkRealm();

        ValueChangingEvent event = new ValueChangingEvent(this, diff);
        fireEvent(event);
        return !event.veto;
    }

    public synchronized void dispose() {
        super.dispose();
    }

}