/*******************************************************************************
 * Copyright (c) 2001, 2004 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
 *******************************************************************************/
package org.eclipse.wst.xsd.ui.internal.properties.section;

import org.eclipse.swt.SWT;
import org.eclipse.swt.widgets.Control;
import org.eclipse.swt.widgets.Event;
import org.eclipse.swt.widgets.Listener;

public abstract class TextChangeHelper implements Listener
{
	private boolean nonUserChange;

	/**
	 * Marks the start of a programmatic change to the widget contents.
	 * Clients must call startNonUserChange() before directly setting 
	 * the widget contents to avoid unwanted lifecycle events.
	 * @throws IllegalArgumentException if a programmatic change is 
	 * already in progress.
	 */
	public void startNonUserChange() {
		if (nonUserChange)
			throw new IllegalStateException("we already started a non user change");//$NON-NLS-1$
		nonUserChange = true;
	}

	/**
	 * Clients who call startNonUserChange() should call 
	 * finishNonUserChange() as soon as possible after the change is done.
	 * @throws IllegalArgumentException if no change is in progress.
	 */
	public void finishNonUserChange() {
		if (!nonUserChange)
			throw new IllegalStateException("we are not in a non user change");//$NON-NLS-1$
		nonUserChange = false;
	}

	/**
	 * Returns true if a programmatic change is in progress.
	 */
	public boolean isNonUserChange() {
		return nonUserChange;
	}

	/**
	 * @see org.eclipse.swt.widgets.Listener#handleEvent(org.eclipse.swt.widgets.Event)
	 */
	public void handleEvent(Event event) {
		switch (event.type) {
			case SWT.KeyDown :
				if (event.character == SWT.CR)
					textChanged((Control)event.widget);
				break;
			case SWT.FocusOut :
				textChanged((Control)event.widget);
				break;
		}
	}

	/**
	 * Abstract method notified when a text field has been changed.
	 * @param control
	 */
	public abstract void textChanged(Control control);

	/**
	 * Registers this helper with the given control to listen for events
	 * which indicate that a change is in progress (or done).
	 */
	public void startListeningTo(Control control) {
		control.addListener(SWT.FocusOut, this);
		control.addListener(SWT.Modify, this);
	}

	/**
	 * Registers this helper with the given control to listen for the
	 * Enter key.  When Enter is pressed, the change is considered done 
	 * (this is only appropriate for single-line Text widgets).
	 */
	public void startListeningForEnter(Control control) {
		// NOTE: KeyDown rather than KeyUp, because of similar usage in CCombo. 
		control.addListener(SWT.KeyDown, this);
	}

	/**
	 * Unregisters this helper from a control previously passed to
	 * startListeningTo() and/or startListeningForEnter().
	 */
	public void stopListeningTo(Control control) {
		control.removeListener(SWT.FocusOut, this);
		control.removeListener(SWT.Modify, this);
		control.removeListener(SWT.KeyDown, this);
	}
}