/*
    * 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.lang.reflect.Method;
  import java.util.Stack;
  
  /**
   * <em>Consider this class private.</em> Provides various methods to determine the caller class. <h3>Background</h3>
   * <p>
   * This method, available only in the Oracle/Sun/OpenJDK implementations of the Java Virtual Machine, is a much more
   * efficient mechanism for determining the {@link Class} of the caller of a particular method. When it is not available,
   * a {@link SecurityManager} is the second-best option. When this is also not possible, the {@code StackTraceElement[]}
   * returned by {@link Throwable#getStackTrace()} must be used, and its {@code String} class name converted to a
   * {@code Class} using the slow {@link Class#forName} (which can add an extra microsecond or more for each invocation
   * depending on the runtime ClassLoader hierarchy).
   * </p>
   * <p>
   * During Java 8 development, the {@code sun.reflect.Reflection.getCallerClass(int)} was removed from OpenJDK, and this
   * change was back-ported to Java 7 in version 1.7.0_25 which changed the behavior of the call and caused it to be off
   * by one stack frame. This turned out to be beneficial for the survival of this API as the change broke hundreds of
   * libraries and frameworks relying on the API which brought much more attention to the intended API removal.
   * </p>
   * <p>
   * After much community backlash, the JDK team agreed to restore {@code getCallerClass(int)} and keep its existing
   * behavior for the rest of Java 7. However, the method is deprecated in Java 8, and current Java 9 development has not
   * addressed this API. Therefore, the functionality of this class cannot be relied upon for all future versions of Java.
   * It does, however, work just fine in Sun JDK 1.6, OpenJDK 1.6, Oracle/OpenJDK 1.7, and Oracle/OpenJDK 1.8. Other Java
   * environments may fall back to using {@link Throwable#getStackTrace()} which is significantly slower due to
   * examination of every virtual frame of execution.
   * </p>
   */
  public final class StackLocator {
  
      // Checkstyle Suppress: the lower-case 'u' ticks off CheckStyle...
      // CHECKSTYLE:OFF
      static final int JDK_7u25_OFFSET;
      // CHECKSTYLE:OFF
  
      private static final Method GET_CALLER_CLASS;
  
      private static final StackLocator INSTANCE;
  
      static {
          Method getCallerClass;
          int java7u25CompensationOffset = 0;
          try {
              final Class<?> sunReflectionClass = LoaderUtil.loadClass("sun.reflect.Reflection");
              getCallerClass = sunReflectionClass.getDeclaredMethod("getCallerClass", int.class);
              Object o = getCallerClass.invoke(null, 0);
              getCallerClass.invoke(null, 0);
              if (o == null || o != sunReflectionClass) {
                  getCallerClass = null;
                  java7u25CompensationOffset = -1;
              } else {
                  o = getCallerClass.invoke(null, 1);
                  if (o == sunReflectionClass) {
                      System.out.println("WARNING: Java 1.7.0_25 is in use which has a broken implementation of Reflection.getCallerClass(). " +
                          " Please consider upgrading to Java 1.7.0_40 or later.");
                      java7u25CompensationOffset = 1;
                  }
              }
          } catch (final Exception | LinkageError e) {
              System.out.println("WARNING: sun.reflect.Reflection.getCallerClass is not supported. This will impact performance.");
              getCallerClass = null;
              java7u25CompensationOffset = -1;
          }
  
          GET_CALLER_CLASS = getCallerClass;
          JDK_7u25_OFFSET = java7u25CompensationOffset;
  
          INSTANCE = new StackLocator();
      }
  
      public static StackLocator getInstance() {
          return INSTANCE;
      }
  
      private StackLocator() {
      }
  
      // TODO: return Object.class instead of null (though it will have a null ClassLoader)
      // (MS) I believe this would work without any modifications elsewhere, but I could be wrong
  
      // migrated from ReflectiveCallerClassUtility
     @PerformanceSensitive
     public Class<?> getCallerClass(final int depth) {
         if (depth < 0) {
             throw new IndexOutOfBoundsException(Integer.toString(depth));
         }
         // note that we need to add 1 to the depth value to compensate for this method, but not for the Method.invoke
         // since Reflection.getCallerClass ignores the call to Method.invoke()
         try {
             return (Class<?>) GET_CALLER_CLASS.invoke(null, depth + 1 + JDK_7u25_OFFSET);
         } catch (final Exception e) {
             // theoretically this could happen if the caller class were native code
             // TODO: return Object.class
             return null;
         }
     }
 
     // migrated from Log4jLoggerFactory
     @PerformanceSensitive
     public Class<?> getCallerClass(final String fqcn, final String pkg) {
         boolean next = false;
         Class<?> clazz;
         for (int i = 2; null != (clazz = getCallerClass(i)); i++) {
             if (fqcn.equals(clazz.getName())) {
                 next = true;
                 continue;
             }
             if (next && clazz.getName().startsWith(pkg)) {
                 return clazz;
             }
         }
         // TODO: return Object.class
         return null;
     }
 
     // added for use in LoggerAdapter implementations mainly
     @PerformanceSensitive
     public Class<?> getCallerClass(final Class<?> anchor) {
         boolean next = false;
         Class<?> clazz;
         for (int i = 2; null != (clazz = getCallerClass(i)); i++) {
             if (anchor.equals(clazz)) {
                 next = true;
                 continue;
             }
             if (next) {
                 return clazz;
             }
         }
         return Object.class;
     }
 
     // migrated from ThrowableProxy
     @PerformanceSensitive
     public Stack<Class<?>> getCurrentStackTrace() {
         // benchmarks show that using the SecurityManager is much faster than looping through getCallerClass(int)
         if (PrivateSecurityManagerStackTraceUtil.isEnabled()) {
             return PrivateSecurityManagerStackTraceUtil.getCurrentStackTrace();
         }
         // slower version using getCallerClass where we cannot use a SecurityManager
         final Stack<Class<?>> classes = new Stack<>();
         Class<?> clazz;
         for (int i = 1; null != (clazz = getCallerClass(i)); i++) {
             classes.push(clazz);
         }
         return classes;
     }
 
     public StackTraceElement calcLocation(final String fqcnOfLogger) {
         if (fqcnOfLogger == null) {
             return null;
         }
         // LOG4J2-1029 new Throwable().getStackTrace is faster than Thread.currentThread().getStackTrace().
         final StackTraceElement[] stackTrace = new Throwable().getStackTrace();
         boolean found = false;
         for (int i = 0; i < stackTrace.length; i++) {
             final String className = stackTrace[i].getClassName();
             if (fqcnOfLogger.equals(className)) {
 
                 found = true;
                 continue;
             }
             if (found && !fqcnOfLogger.equals(className)) {
                 return stackTrace[i];
             }
         }
         return null;
     }
 
     public StackTraceElement getStackTraceElement(final int depth) {
         // (MS) I tested the difference between using Throwable.getStackTrace() and Thread.getStackTrace(), and
         // the version using Throwable was surprisingly faster! at least on Java 1.8. See ReflectionBenchmark.
         final StackTraceElement[] elements = new Throwable().getStackTrace();
         int i = 0;
         for (final StackTraceElement element : elements) {
             if (isValid(element)) {
                 if (i == depth) {
                     return element;
                 }
                 ++i;
             }
         }
         throw new IndexOutOfBoundsException(Integer.toString(depth));
     }
 
     private boolean isValid(final StackTraceElement element) {
         // ignore native methods (oftentimes are repeated frames)
         if (element.isNativeMethod()) {
             return false;
         }
         final String cn = element.getClassName();
         // ignore OpenJDK internal classes involved with reflective invocation
         if (cn.startsWith("sun.reflect.")) {
             return false;
         }
         final String mn = element.getMethodName();
         // ignore use of reflection including:
         // Method.invoke
         // InvocationHandler.invoke
         // Constructor.newInstance
         if (cn.startsWith("java.lang.reflect.") && (mn.equals("invoke") || mn.equals("newInstance"))) {
             return false;
         }
         // ignore use of Java 1.9+ reflection classes
         if (cn.startsWith("jdk.internal.reflect.")) {
             return false;
         }
         // ignore Class.newInstance
         if (cn.equals("java.lang.Class") && mn.equals("newInstance")) {
             return false;
         }
         // ignore use of Java 1.7+ MethodHandle.invokeFoo() methods
         if (cn.equals("java.lang.invoke.MethodHandle") && mn.startsWith("invoke")) {
             return false;
         }
         // any others?
         return true;
     }
 }