/*******************************************************************************
 * Copyright (c) 2005, 2008 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 137877
 *     Brad Reynolds - bug 164653
 *     Brad Reynolds - bug 147515
 *     Ashley Cambrell - bug 198906
 *******************************************************************************/

module org.eclipse.jface.internal.databinding.viewers.SelectionProviderSingleSelectionObservableValue;

import java.lang.all;

import org.eclipse.core.databinding.observable.Diffs;
import org.eclipse.core.databinding.observable.Realm;
import org.eclipse.core.databinding.observable.value.AbstractObservableValue;
import org.eclipse.jface.util.Util;
import org.eclipse.jface.viewers.ISelection;
import org.eclipse.jface.viewers.ISelectionChangedListener;
import org.eclipse.jface.viewers.ISelectionProvider;
import org.eclipse.jface.viewers.IStructuredSelection;
import org.eclipse.jface.viewers.SelectionChangedEvent;
import org.eclipse.jface.viewers.StructuredSelection;

/**
 * Observes single selection of an <code>ISelectionProvider</code>.
 *
 * @since 1.1
 */
public class SelectionProviderSingleSelectionObservableValue :
        AbstractObservableValue {

    private final ISelectionProvider selectionProvider;

    private bool updating = false;

    private Object currentSelection;

    private ISelectionChangedListener selectionChangedListener;

    /**
     * Constructs a new instance associated with the provided
     * <code>selectionProvider</code>. In order to initialize itself properly
     * the constructor invokes {@link #doGetValue()}. This could be dangerous
     * for subclasses, see {@link #doGetValue()} for an explanation.
     *
     * @param realm
     *
     * @param selectionProvider
     * @see #doGetValue()
     */
    public this(Realm realm,
            ISelectionProvider selectionProvider) {
        super(realm);
        if (selectionProvider is null) {
            throw new IllegalArgumentException(
                    "The 'selectionProvider' parameter is null."); //$NON-NLS-1$
        }

        this.selectionProvider = selectionProvider;
        this.currentSelection = doGetValue();

        selectionChangedListener = new class() ISelectionChangedListener {
            public void selectionChanged(SelectionChangedEvent event) {
                if (!updating) {
                    Object oldSelection = currentSelection;
                    currentSelection = doGetValue();
                    fireValueChange(Diffs.createValueDiff(oldSelection,
                            currentSelection));
                }
            }
        };
        selectionProvider.addSelectionChangedListener(selectionChangedListener);
    }

    /**
     * Sets the selection to the provided <code>value</code>. Value change
     * events are fired after selection is set in the selection provider.
     *
     * @param value
     *            object to set as selected, <code>null</code> if wanting to
     *            remove selection
     */
    public void doSetValue(Object value) {
        try {
            updating = true;

            Object oldSelection = currentSelection;
            selectionProvider
                    .setSelection(value is null ? StructuredSelection.EMPTY
                            : new StructuredSelection(value));
            currentSelection = doGetValue();
            if (!Util.equals(oldSelection, currentSelection)) {
                fireValueChange(Diffs.createValueDiff(oldSelection,
                        currentSelection));
            }
        } finally {
            updating = false;
        }
    }

    /**
     * Retrieves the current selection.
     * <p>
     * If a subclass overrides this method it must not depend upon the subclass
     * to have been fully initialized before this method is invoked.
     * <code>doGetValue()</code> is invoked by the
     * {@link #SelectionProviderSingleSelectionObservableValue(Realm, ISelectionProvider) constructor}
     * which means the subclass's constructor will not have fully executed
     * before this method is invoked.
     * </p>
     *
     * @return selection will be an instance of
     *         <code>IStructuredSelection</code> if a selection exists,
     *         <code>null</code> if no selection
     * @see #SelectionProviderSingleSelectionObservableValue(Realm,
     *      ISelectionProvider)
     */
    protected Object doGetValue() {
        ISelection selection = selectionProvider.getSelection();
        if (null !is cast(IStructuredSelection)selection) {
            IStructuredSelection sel = cast(IStructuredSelection) selection;
            return sel.getFirstElement();
        }

        return null;
    }

    public Object getValueType() {
        return null;
    }

    /*
     * (non-Javadoc)
     *
     * @see org.eclipse.core.databinding.observable.value.AbstractObservableValue#dispose()
     */
    public synchronized void dispose() {
        selectionProvider
                .removeSelectionChangedListener(selectionChangedListener);
        super.dispose();
    }
}