/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF 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
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * 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.apache.flink.contrib.streaming.state;

import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.TemporaryFolder;
import org.rocksdb.RocksDB;

import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;

import static org.junit.Assert.*;

/**
 * This test validates that the RocksDB JNI library loading works properly
 * in the presence of the RocksDB code being loaded dynamically via reflection.
 * That can happen when RocksDB is in the user code JAR, or in certain test setups.
 */
public class RocksDbMultiClassLoaderTest {

	@Rule
	public final TemporaryFolder tmp = new TemporaryFolder();

	@Test
	public void testTwoSeparateClassLoaders() throws Exception {
		// collect the libraries / class folders with RocksDB related code: the state backend and RocksDB itself
		final URL codePath1 = RocksDBStateBackend.class.getProtectionDomain().getCodeSource().getLocation();
		final URL codePath2 = RocksDB.class.getProtectionDomain().getCodeSource().getLocation();

		final ClassLoader parent = getClass().getClassLoader();
		final ClassLoader loader1 = new ChildFirstClassLoader(new URL[] { codePath1, codePath2 }, parent);
		final ClassLoader loader2 = new ChildFirstClassLoader(new URL[] { codePath1, codePath2 }, parent);

		final String className = RocksDBStateBackend.class.getName();

		final Class<?> clazz1 = Class.forName(className, false, loader1);
		final Class<?> clazz2 = Class.forName(className, false, loader2);
		assertNotEquals("Test broken - the two reflectively loaded classes are equal", clazz1, clazz2);

		final Object instance1 = clazz1.getConstructor(String.class).newInstance(tmp.newFolder().toURI().toString());
		final Object instance2 = clazz2.getConstructor(String.class).newInstance(tmp.newFolder().toURI().toString());

		final String tempDir = tmp.newFolder().getAbsolutePath();

 		final Method meth1 = clazz1.getDeclaredMethod("ensureRocksDBIsLoaded", String.class);
		final Method meth2 = clazz2.getDeclaredMethod("ensureRocksDBIsLoaded", String.class);
		meth1.setAccessible(true);
		meth2.setAccessible(true);

		// if all is well, these methods can both complete successfully
		meth1.invoke(instance1, tempDir);
		meth2.invoke(instance2, tempDir);
	}

	// ------------------------------------------------------------------------

	/**
	 * A variant of the URLClassLoader that first loads from the URLs and only after that from the parent.
	 */
	private static final class ChildFirstClassLoader extends URLClassLoader {

		private final ClassLoader parent;

		public ChildFirstClassLoader(URL[] urls, ClassLoader parent) {
			super(urls, null);
			this.parent = parent;
		}

		@Override
		public Class<?> findClass(String name) throws ClassNotFoundException {
			// first try to load from the URLs
			// because the URLClassLoader's parent is null, this cannot implicitly load from the parent
			try {
				return super.findClass(name);
			}
			catch (ClassNotFoundException e) {
				// not in the URL, check the parent
				return parent.loadClass(name);
			}
		}
	}
}