/*******************************************************************************
 * Copyright (c) 2006 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.help.ui.internal;

import org.eclipse.core.expressions.EvaluationContext;
import org.eclipse.core.runtime.Platform;
import org.eclipse.ui.PlatformUI;

/*
 * Supplies en evaluation context for filtering help documents when running in
 * workbench mode. This is used for resolving variables in enablement expressions.
 */
public final class HelpUIEvaluationContext {

	private static final String VARIABLE_PLATFORM = "platform"; //$NON-NLS-1$
	private static final String VARIABLE_WORKBENCH = "workbench"; //$NON-NLS-1$
	
	private static EvaluationContext context;
	
	/*
	 * Returns the evaluation context to use in help documents.
	 */
	public static EvaluationContext getContext() {
		if (context == null) {
			context = new EvaluationContext(null, Platform.class) {
				public Object getVariable(String name) {
					if (VARIABLE_PLATFORM.equals(name)) {
						return Platform.class;
					}
					else if (VARIABLE_WORKBENCH.equals(name)) {
						return PlatformUI.getWorkbench();
					}
					return null;
				}
			};
		}
		return context;
	}

	/*
	 * Not meant to be instantiated.
	 */
	private HelpUIEvaluationContext() {
	}
}
