Copyright (c) 2005, 2016 IBM Corporation and others.
This program and the accompanying materials
are made available under the terms of the Eclipse Public License 2.0
which accompanies this distribution, and is available at
https://www.eclipse.org/legal/epl-2.0/
SPDX-License-Identifier: EPL-2.0
Contributors:
    IBM Corporation - initial API and implementation
/*******************************************************************************
 * Copyright (c) 2005, 2016 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 * 
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.osgi.internal.loader.buddy;

import java.io.IOException;
import java.net.URL;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Enumeration;

public class SystemPolicy implements IBuddyPolicy {

	public static final byte BOOT = 0;
	public static final byte EXT = 1;
	public static final byte APP = 2;

	private static SystemPolicy[] instances = new SystemPolicy[3];

	private ClassLoader classLoader;

	public static SystemPolicy getInstance(final byte type, final ClassLoader bootLoader) {
		if (instances[type] == null) {
			instances[type] = new SystemPolicy();
			instances[type].classLoader = AccessController.doPrivileged(new PrivilegedAction<ClassLoader>() {
				@Override
				public ClassLoader run() {
					return createClassLoader(type, bootLoader);
				}
			});
		}
		return instances[type];
	}

	public SystemPolicy() {
		//Nothing to do
	}

	public SystemPolicy(ClassLoader parent) {
		classLoader = parent;
	}

	static ClassLoader createClassLoader(byte type, ClassLoader bootLoader) {
		switch (type) {
			case APP :
				if (ClassLoader.getSystemClassLoader() != null)
					return ClassLoader.getSystemClassLoader();
				return bootLoader;

			case BOOT :
				return bootLoader;

			case EXT :
				if (ClassLoader.getSystemClassLoader() != null)
					return ClassLoader.getSystemClassLoader().getParent();
				return bootLoader;
		}
		return null;
	}

	@Override
	public Class<?> loadClass(String name) {
		try {
			return classLoader.loadClass(name);
		} catch (ClassNotFoundException e) {
			return null;
		}
	}

	@Override
	public URL loadResource(String name) {
		return classLoader.getResource(name);
	}

	@Override
	public Enumeration<URL> loadResources(String name) {
		try {
			return classLoader.getResources(name);
		} catch (IOException e) {
			return null;
		}
	}

}