/**
 * Licensed to Apereo under one or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information regarding copyright ownership. Apereo
 * licenses this file to you under the Apache License, Version 2.0 (the "License"); you may not use
 * this file except in compliance with the License. You may obtain a copy of the License at the
 * following location:
 *
 * <p>http://www.apache.org/licenses/LICENSE-2.0
 *
 * <p>Unless required by applicable law or agreed to in writing, software distributed under the
 * License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
 * express or implied. See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apereo.portal.portlet.dao.jpa;

import java.util.Deque;
import java.util.LinkedList;
import org.aspectj.lang.ProceedingJoinPoint;
import org.springframework.core.Ordered;

/**
 * Switches context class loader for {@link Thread#currentThread()} to the class loader of this
 * class and switches it back after the method completes
 *
 */
public class ThreadContextClassLoaderAspect implements Ordered {
    private static final ClassLoader PORTAL_CLASS_LOADER =
            ThreadContextClassLoaderAspect.class.getClassLoader();
    private static final ThreadLocal<Deque<ClassLoader>> PREVIOUS_CLASS_LOADER =
            new ThreadLocal<Deque<ClassLoader>>();

    public static ClassLoader getPreviousClassLoader() {
        final Deque<ClassLoader> deque = PREVIOUS_CLASS_LOADER.get();
        if (deque == null) {
            return null;
        }

        return deque.peekFirst();
    }

    @Override
    public int getOrder() {
        return Ordered.HIGHEST_PRECEDENCE;
    }

    /**
     * Wraps the targeted execution, switching the current thread's context class loader to this
     * classes class loader. Usage defined in persistanceContext.xml.
     */
    public Object doThreadContextClassLoaderUpdate(ProceedingJoinPoint pjp) throws Throwable {
        final Thread currentThread = Thread.currentThread();
        final ClassLoader previousClassLoader = currentThread.getContextClassLoader();
        Deque<ClassLoader> deque = PREVIOUS_CLASS_LOADER.get();
        if (deque == null) {
            deque = new LinkedList<ClassLoader>();
            PREVIOUS_CLASS_LOADER.set(deque);
        }

        deque.push(previousClassLoader);

        try {
            currentThread.setContextClassLoader(PORTAL_CLASS_LOADER);
            return pjp.proceed();
        } finally {
            currentThread.setContextClassLoader(previousClassLoader);
            deque.removeFirst();
            if (deque.isEmpty()) {
                //clean up the threadlocal when the deque is empty
                PREVIOUS_CLASS_LOADER.remove();
            }
        }
    }
}