/*
 * 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.geode.modules.util;

import static org.assertj.core.api.Assertions.*;

import org.apache.bcel.Constants;
import org.apache.bcel.classfile.JavaClass;
import org.apache.bcel.generic.ClassGen;
import org.apache.geode.internal.ClassPathLoader;
import org.apache.geode.test.junit.categories.UnitTest;
import org.junit.After;
import org.junit.Before;
import org.junit.Rule;
import org.junit.Test;
import org.junit.experimental.categories.Category;
import org.junit.rules.TestName;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.net.URL;
import java.util.Enumeration;
import java.util.Vector;

@Category(UnitTest.class)
@SuppressWarnings("unused")
public class ClassLoaderObjectInputStreamTest {

  private ClassLoader originalTCCL;
  private ClassLoader newTCCL;
  private String classToLoad;
  private Object instanceOfTCCLClass;

  @Rule
  public TestName testName = new TestName();

  @Before
  public void setUp() throws Exception {
    this.originalTCCL = Thread.currentThread().getContextClassLoader();
    this.newTCCL = new GeneratingClassLoader();
    this.classToLoad = "com.nowhere." + getClass().getSimpleName() + "_" + testName.getMethodName();
    this.instanceOfTCCLClass = createInstanceOfTCCLClass();
  }

  @After
  public void unsetTCCL() throws Exception {
    Thread.currentThread().setContextClassLoader(this.originalTCCL);
  }

  @Test
  public void resolveClassFromTCCLThrowsIfTCCLDisabled() throws Exception {
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    ObjectOutputStream oos = new ObjectOutputStream(baos);
    oos.writeObject(this.instanceOfTCCLClass);
    oos.close();

    ObjectInputStream ois = new ClassLoaderObjectInputStream(
        new ByteArrayInputStream(baos.toByteArray()), getClass().getClassLoader());

    assertThatThrownBy(() -> ois.readObject()).isExactlyInstanceOf(ClassNotFoundException.class);
  }

  @Test
  public void resolveClassFindsClassFromTCCLIfTCCLEnabled() throws Exception {
    Thread.currentThread().setContextClassLoader(this.newTCCL);

    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    ObjectOutputStream oos = new ObjectOutputStream(baos);
    oos.writeObject(this.instanceOfTCCLClass);
    oos.close();

    ObjectInputStream ois = new ClassLoaderObjectInputStream(
        new ByteArrayInputStream(baos.toByteArray()), getClass().getClassLoader());

    Object objectFromTCCL = ois.readObject();

    assertThat(objectFromTCCL).isNotNull();
    assertThat(objectFromTCCL.getClass()).isNotNull();
    assertThat(objectFromTCCL.getClass().getName()).isEqualTo(this.classToLoad);
  }

  private Object createInstanceOfTCCLClass()
      throws ClassNotFoundException, IllegalAccessException, InstantiationException {
    Class<?> clazz = Class.forName(this.classToLoad, false, this.newTCCL);
    return clazz.newInstance();
  }

  /**
   * Custom class loader which uses BCEL to always dynamically generate a class for any class name
   * it tries to load.
   */
  private static class GeneratingClassLoader extends ClassLoader {

    /**
     * Currently unused but potentially useful for some future test. This causes this loader to only
     * generate a class that the parent could not find.
     *
     * @param parent the parent class loader to check with first
     */
    public GeneratingClassLoader(ClassLoader parent) {
      super(parent);
    }

    /**
     * Specifies no parent to ensure that this loader generates the named class.
     */
    public GeneratingClassLoader() {
      super(null); // no parent
    }

    @Override
    protected Class<?> findClass(String name) throws ClassNotFoundException {
      ClassGen cg = new ClassGen(name, Object.class.getName(), "<generated>",
          Constants.ACC_PUBLIC | Constants.ACC_SUPER, new String[] {Serializable.class.getName()});
      cg.addEmptyConstructor(Constants.ACC_PUBLIC);
      JavaClass jClazz = cg.getJavaClass();
      byte[] bytes = jClazz.getBytes();
      return defineClass(jClazz.getClassName(), bytes, 0, bytes.length);
    }

    @Override
    protected URL findResource(String name) {
      URL url = null;
      try {
        url = getTempFile().getAbsoluteFile().toURI().toURL();
        System.out.println("GeneratingClassLoader#findResource returning " + url);
      } catch (IOException e) {
        throw new Error(e);
      }
      return url;
    }

    @Override
    protected Enumeration<URL> findResources(String name) throws IOException {
      URL url;
      try {
        url = getTempFile().getAbsoluteFile().toURI().toURL();
        System.out.println("GeneratingClassLoader#findResources returning " + url);
      } catch (IOException e) {
        throw new Error(e);
      }
      Vector<URL> urls = new Vector<URL>();
      urls.add(url);
      return urls.elements();
    }

    protected File getTempFile() {
      return null;
    }
  }

}