/*
    * 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.logging.log4j.util;
  
  import java.io.IOException;
  import java.lang.reflect.InvocationTargetException;
  import java.net.URL;
  import java.security.AccessController;
  import java.security.PrivilegedAction;
  import java.util.Collection;
  import java.util.Enumeration;
  import java.util.LinkedHashSet;
  import java.util.Objects;
  
  /**
   * <em>Consider this class private.</em> Utility class for ClassLoaders.
   *
   * @see ClassLoader
   * @see RuntimePermission
   * @see Thread#getContextClassLoader()
   * @see ClassLoader#getSystemClassLoader()
   */
  public final class LoaderUtil {
  
      /**
       * System property to set to ignore the thread context ClassLoader.
       *
       * @since 2.1
       */
      public static final String IGNORE_TCCL_PROPERTY = "log4j.ignoreTCL";
  
      private static final SecurityManager SECURITY_MANAGER = System.getSecurityManager();
  
      // this variable must be lazily loaded; otherwise, we get a nice circular class loading problem where LoaderUtil
      // wants to use PropertiesUtil, but then PropertiesUtil wants to use LoaderUtil.
      private static Boolean ignoreTCCL;
  
      private static final boolean GET_CLASS_LOADER_DISABLED;
  
      private static final PrivilegedAction<ClassLoader> TCCL_GETTER = new ThreadContextClassLoaderGetter();
  
      static {
          if (SECURITY_MANAGER != null) {
              boolean getClassLoaderDisabled;
              try {
                  SECURITY_MANAGER.checkPermission(new RuntimePermission("getClassLoader"));
                  getClassLoaderDisabled = false;
              } catch (final SecurityException ignored) {
                  getClassLoaderDisabled = true;
              }
              GET_CLASS_LOADER_DISABLED = getClassLoaderDisabled;
          } else {
              GET_CLASS_LOADER_DISABLED = false;
          }
      }
  
      private LoaderUtil() {
      }
  
      /**
       * Gets the current Thread ClassLoader. Returns the system ClassLoader if the TCCL is {@code null}. If the system
       * ClassLoader is {@code null} as well, then the ClassLoader for this class is returned. If running with a
       * {@link SecurityManager} that does not allow access to the Thread ClassLoader or system ClassLoader, then the
       * ClassLoader for this class is returned.
       *
       * @return the current ThreadContextClassLoader.
       */
      public static ClassLoader getThreadContextClassLoader() {
          if (GET_CLASS_LOADER_DISABLED) {
              // we can at least get this class's ClassLoader regardless of security context
              // however, if this is null, there's really no option left at this point
              return LoaderUtil.class.getClassLoader();
          }
          return SECURITY_MANAGER == null ? TCCL_GETTER.run() : AccessController.doPrivileged(TCCL_GETTER);
      }
  
      /**
       *
       */
      private static class ThreadContextClassLoaderGetter implements PrivilegedAction<ClassLoader> {
          @Override
          public ClassLoader run() {
              final ClassLoader cl = Thread.currentThread().getContextClassLoader();
              if (cl != null) {
                  return cl;
             }
             final ClassLoader ccl = LoaderUtil.class.getClassLoader();
             return ccl == null && !GET_CLASS_LOADER_DISABLED ? ClassLoader.getSystemClassLoader() : ccl;
         }
     }
 
     public static ClassLoader[] getClassLoaders() {
         final Collection<ClassLoader> classLoaders = new LinkedHashSet<>();
         final ClassLoader tcl = getThreadContextClassLoader();
         if (tcl != null) {
             classLoaders.add(tcl);
         }
         accumulateClassLoaders(LoaderUtil.class.getClassLoader(), classLoaders);
         accumulateClassLoaders(tcl == null ? null : tcl.getParent(), classLoaders);
         final ClassLoader systemClassLoader = ClassLoader.getSystemClassLoader();
 		if (systemClassLoader != null) {
             classLoaders.add(systemClassLoader);
         }
         return classLoaders.toArray(new ClassLoader[classLoaders.size()]);
     }
 
     /**
      * Adds the provided loader to the loaders collection, and traverses up the tree until either a null
      * value or a classloader which has already been added is encountered.
      */
     private static void accumulateClassLoaders(ClassLoader loader, Collection<ClassLoader> loaders) {
         // Some implementations may use null to represent the bootstrap class loader.
         if (loader != null && loaders.add(loader)) {
             accumulateClassLoaders(loader.getParent(), loaders);
         }
     }
 
     /**
      * Determines if a named Class can be loaded or not.
      *
      * @param className The class name.
      * @return {@code true} if the class could be found or {@code false} otherwise.
      * @since 2.7
      */
     public static boolean isClassAvailable(final String className) {
         try {
             final Class<?> clazz = loadClass(className);
             return clazz != null;
         } catch (final ClassNotFoundException | LinkageError e) {
             return false;
         } catch (final Throwable e) {
             LowLevelLogUtil.logException("Unknown error checking for existence of class: " + className, e);
             return false;
         }
     }
 
     /**
      * Loads a class by name. This method respects the {@link #IGNORE_TCCL_PROPERTY} Log4j property. If this property is
      * specified and set to anything besides {@code false}, then the default ClassLoader will be used.
      *
      * @param className The class name.
      * @return the Class for the given name.
      * @throws ClassNotFoundException if the specified class name could not be found
      * @since 2.1
      */
     public static Class<?> loadClass(final String className) throws ClassNotFoundException {
         if (isIgnoreTccl()) {
             return Class.forName(className);
         }
         try {
             ClassLoader tccl = getThreadContextClassLoader();
             if (tccl != null) {
                 return tccl.loadClass(className);
             }
         } catch (final Throwable ignored) {
         }
         return Class.forName(className);
     }
 
     /**
      * Loads and instantiates a Class using the default constructor.
      *
      * @param clazz The class.
      * @return new instance of the class.
      * @throws IllegalAccessException if the class can't be instantiated through a public constructor
      * @throws InstantiationException if there was an exception whilst instantiating the class
      * @throws InvocationTargetException if there was an exception whilst constructing the class
      * @since 2.7
      */
     public static <T> T newInstanceOf(final Class<T> clazz)
             throws InstantiationException, IllegalAccessException, InvocationTargetException {
         try {
             return clazz.getConstructor().newInstance();
         } catch (final NoSuchMethodException ignored) {
             // FIXME: looking at the code for Class.newInstance(), this seems to do the same thing as above
             return clazz.newInstance();
         }
     }
 
     /**
      * Loads and instantiates a Class using the default constructor.
      *
      * @param className The class name.
      * @return new instance of the class.
      * @throws ClassNotFoundException if the class isn't available to the usual ClassLoaders
      * @throws IllegalAccessException if the class can't be instantiated through a public constructor
      * @throws InstantiationException if there was an exception whilst instantiating the class
      * @throws NoSuchMethodException if there isn't a no-args constructor on the class
      * @throws InvocationTargetException if there was an exception whilst constructing the class
      * @since 2.1
      */
     @SuppressWarnings("unchecked")
     public static <T> T newInstanceOf(final String className) throws ClassNotFoundException, IllegalAccessException,
             InstantiationException, NoSuchMethodException, InvocationTargetException {
         return newInstanceOf((Class<T>) loadClass(className));
     }
 
     /**
      * Loads and instantiates a derived class using its default constructor.
      *
      * @param className The class name.
      * @param clazz The class to cast it to.
      * @param <T> The type of the class to check.
      * @return new instance of the class cast to {@code T}
      * @throws ClassNotFoundException if the class isn't available to the usual ClassLoaders
      * @throws IllegalAccessException if the class can't be instantiated through a public constructor
      * @throws InstantiationException if there was an exception whilst instantiating the class
      * @throws NoSuchMethodException if there isn't a no-args constructor on the class
      * @throws InvocationTargetException if there was an exception whilst constructing the class
      * @throws ClassCastException if the constructed object isn't type compatible with {@code T}
      * @since 2.1
      */
     public static <T> T newCheckedInstanceOf(final String className, final Class<T> clazz)
             throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException,
             IllegalAccessException {
         return clazz.cast(newInstanceOf(className));
     }
 
     /**
      * Loads and instantiates a class given by a property name.
      *
      * @param propertyName The property name to look up a class name for.
      * @param clazz        The class to cast it to.
      * @param <T>          The type to cast it to.
      * @return new instance of the class given in the property or {@code null} if the property was unset.
      * @throws ClassNotFoundException    if the class isn't available to the usual ClassLoaders
      * @throws IllegalAccessException    if the class can't be instantiated through a public constructor
      * @throws InstantiationException    if there was an exception whilst instantiating the class
      * @throws NoSuchMethodException     if there isn't a no-args constructor on the class
      * @throws InvocationTargetException if there was an exception whilst constructing the class
      * @throws ClassCastException        if the constructed object isn't type compatible with {@code T}
      * @since 2.5
      */
     public static <T> T newCheckedInstanceOfProperty(final String propertyName, final Class<T> clazz)
         throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException,
         IllegalAccessException {
         final String className = PropertiesUtil.getProperties().getStringProperty(propertyName);
         if (className == null) {
             return null;
         }
         return newCheckedInstanceOf(className, clazz);
     }
 
     private static boolean isIgnoreTccl() {
         // we need to lazily initialize this, but concurrent access is not an issue
         if (ignoreTCCL == null) {
             final String ignoreTccl = PropertiesUtil.getProperties().getStringProperty(IGNORE_TCCL_PROPERTY, null);
             ignoreTCCL = ignoreTccl != null && !"false".equalsIgnoreCase(ignoreTccl.trim());
         }
         return ignoreTCCL;
     }
 
     /**
      * Finds classpath {@linkplain URL resources}.
      *
      * @param resource the name of the resource to find.
      * @return a Collection of URLs matching the resource name. If no resources could be found, then this will be empty.
      * @since 2.1
      */
     public static Collection<URL> findResources(final String resource) {
         final Collection<UrlResource> urlResources = findUrlResources(resource);
         final Collection<URL> resources = new LinkedHashSet<>(urlResources.size());
         for (final UrlResource urlResource : urlResources) {
             resources.add(urlResource.getUrl());
         }
         return resources;
     }
 
     static Collection<UrlResource> findUrlResources(final String resource) {
         // @formatter:off
         final ClassLoader[] candidates = {
                 getThreadContextClassLoader(), 
                 LoaderUtil.class.getClassLoader(),
                 GET_CLASS_LOADER_DISABLED ? null : ClassLoader.getSystemClassLoader()};
         // @formatter:on
         final Collection<UrlResource> resources = new LinkedHashSet<>();
         for (final ClassLoader cl : candidates) {
             if (cl != null) {
                 try {
                     final Enumeration<URL> resourceEnum = cl.getResources(resource);
                     while (resourceEnum.hasMoreElements()) {
                         resources.add(new UrlResource(cl, resourceEnum.nextElement()));
                     }
                 } catch (final IOException e) {
                     LowLevelLogUtil.logException(e);
                 }
             }
         }
         return resources;
     }
 
     /**
      * {@link URL} and {@link ClassLoader} pair.
      */
     static class UrlResource {
         private final ClassLoader classLoader;
         private final URL url;
 
         UrlResource(final ClassLoader classLoader, final URL url) {
             this.classLoader = classLoader;
             this.url = url;
         }
 
         public ClassLoader getClassLoader() {
             return classLoader;
         }
 
         public URL getUrl() {
             return url;
         }
 
         @Override
         public boolean equals(final Object o) {
             if (this == o) {
                 return true;
             }
             if (o == null || getClass() != o.getClass()) {
                 return false;
             }
 
             final UrlResource that = (UrlResource) o;
 
             if (classLoader != null ? !classLoader.equals(that.classLoader) : that.classLoader != null) {
                 return false;
             }
             if (url != null ? !url.equals(that.url) : that.url != null) {
                 return false;
             }
 
             return true;
         }
 
         @Override
         public int hashCode() {
             return Objects.hashCode(classLoader) + Objects.hashCode(url);
         }
     }
 }