CpAbstractExtensionFactory.java

/*******************************************************************************
 * Copyright (c) 2016 ARM Ltd. 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:
 * ARM Ltd and ARM Germany GmbH - Initial API and implementation
 *******************************************************************************/

package com.arm.cmsis.pack;

import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;

import org.eclipse.core.runtime.CoreException;
import org.eclipse.core.runtime.IConfigurationElement;
import org.eclipse.core.runtime.IExtension;
import org.eclipse.core.runtime.IStatus;
import org.eclipse.core.runtime.Platform;
import org.eclipse.core.runtime.Status;

/**
 * Base class to handle creation of objects contributed via com.arm.cmsis.pack.* extension points
 */
public abstract class CpAbstractExtensionFactory<T> {

	public static final String ID = "id"; //$NON-NLS-1$
	public static final String CLASS = "class"; //$NON-NLS-1$
	protected Map<String, IConfigurationElement> elements = new HashMap<String, IConfigurationElement>();
	protected T fExtender = null;

	protected CpAbstractExtensionFactory(String extensionPointId) {
		initialize(extensionPointId);
	}

	protected String getExtensionPointId(String elementId) {
		return CpPlugIn.PLUGIN_ID + '.' + elementId;
	}

	/**
	 *  Loads extension point data
	 */
	private void initialize(String elementId) {
		String extensionPointId = getExtensionPointId(elementId);
		IExtension[] extensions = Platform.getExtensionRegistry().getExtensionPoint(extensionPointId).getExtensions();
		for(IExtension extension : extensions) {
			IConfigurationElement[] configElements = extension.getConfigurationElements();
			for(IConfigurationElement config : configElements) {
				String configName = config.getName();
				if (configName.equals(elementId)) {
					String id = config.getAttribute(ID);
					elements.put(id, config);
				}
			}
		}
	}

	/**
	 * Returns extender, instantiates it if needed
	 * @return T
	 */
	public synchronized T getExtender(){
		if(fExtender == null){
			fExtender = createExtender();
		}
		return fExtender;
	}

	protected T createExtender() {
		IConfigurationElement element = null;
		T extender = null;
		for(Entry<String, IConfigurationElement> e : elements.entrySet()) {
			String id = e.getKey();
			IConfigurationElement elem = e.getValue();
			// Prioritize non-ARM extenders
			if(element == null || !id.startsWith(CpPlugIn.PLUGIN_ID)) {
				element = elem;
			}
		}
		if(element != null) {
			try {
				extender = createExtender(element);
			} catch (CoreException e1) {
				e1.printStackTrace();
			}
		}
		return extender;
	}

	protected T createExtender(IConfigurationElement element) throws CoreException{
		if(element == null) {
			return null;
		}
		Object obj = element.createExecutableExtension(CLASS);
		T extender = castToExtenderClass(obj);
		if(extender != null){
			return castToExtenderClass(obj);
		}
		Status status = new Status(IStatus.ERROR, CpPlugIn.PLUGIN_ID, "Invalid extension class specified"); //$NON-NLS-1$
		throw new CoreException(status);
	}

	protected abstract T castToExtenderClass(Object extender);

}