package org.apache.tuscany.sca.osgi.core.impl;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.security.AccessController;
import java.security.PrivilegedAction;

import org.osgi.framework.Bundle;

public class ClassloaderHook {

	/**
	 * Return the BundleContext Classloader for the specified bundle.
	 * 
	 * @param bundle The bundle whose BundleContext is desired.
	 * @return The BundleContext classloader for the specified bundle.
	 */
	ClassLoader getClassLoader(final Bundle bundle) {
		if (System.getSecurityManager() == null) {
			Object bundleLoader =  invokeMethod(bundle, "checkLoader", null, null); //$NON-NLS-1$
			return (ClassLoader) invokeMethod(bundleLoader, "createClassLoader", null, null); //$NON-NLS-1$
		}
		return (ClassLoader) AccessController.doPrivileged(new PrivilegedAction() {
			public Object run() {
				Object bundleLoader =  invokeMethod(bundle, "checkLoader", null, null); //$NON-NLS-1$
				return (ClassLoader) invokeMethod(bundleLoader, "createClassLoader", null, null); //$NON-NLS-1$
			}
		});
	}

	/**
	 * Throws an IllegalStateException if the reflection logic cannot find what
	 * it is looking for. This probably means this class does not properly
	 * recognize the framework implementation.
	 * 
	 * @param e Exception which indicates the reflection logic is confused.
	 */
	protected void reflectionException(Exception e) {
		throw new IllegalStateException("ClassLoaderHook does not recognize the framework implementation: " + e.getMessage());
	}
	
	private Object invokeMethod(Object target, String methodName, Class[] parms, Object[] args){
		Method method;
		try {
			method = target.getClass().getMethod(methodName, parms);
			if(method != null){
				return method.invoke(target,parms,args);
			}
		} catch (SecurityException e) {
			reflectionException(e);
		} catch (NoSuchMethodException e) {
			reflectionException(e);
		} catch (IllegalArgumentException e) {
			reflectionException(e);
		} catch (IllegalAccessException e) {
			reflectionException(e);
		} catch (InvocationTargetException e) {
			reflectionException(e);
		}
		return null;
	}
	

}