/*
    * Copyright 2012 The Netty Project
    *
    * The Netty Project 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.jboss.netty.util.internal;
  
  import java.security.AccessController;
  import java.security.PrivilegedActionException;
  import java.security.PrivilegedExceptionAction;
  import java.util.Queue;
  import java.util.concurrent.BlockingQueue;
  import java.util.concurrent.atomic.AtomicInteger;
  
  /**
   * Utility that detects various properties specific to the current runtime
   * environment, such as Java version and the availability of the
   * {@code sun.misc.Unsafe} object.
   *
   * <br>
   * You can disable the use of {@code sun.misc.Unsafe} if you specify
   * the System property <strong>org.jboss.netty.tryUnsafe</strong> with
   * value of <code>false</code>. Default is <code>true</code>.
   */
  public final class DetectionUtil {
  
      private static final int JAVA_VERSION = javaVersion0();
      private static final boolean HAS_UNSAFE = hasUnsafe(AtomicInteger.class.getClassLoader());
      private static final boolean IS_WINDOWS;
      static {
          String os = SystemPropertyUtil.get("os.name", "").toLowerCase();
          // windows
          IS_WINDOWS =  os.contains("win");
      }
  
      /**
       * Return <code>true</code> if the JVM is running on Windows
       *
       */
      public static boolean isWindows() {
          return IS_WINDOWS;
      }
  
      public static boolean hasUnsafe() {
          return HAS_UNSAFE;
      }
  
      public static int javaVersion() {
          return JAVA_VERSION;
      }
  
      private static boolean hasUnsafe(ClassLoader loader) {
          boolean noUnsafe = SystemPropertyUtil.getBoolean("io.netty.noUnsafe", false);
          if (noUnsafe) {
              return false;
          }
  
          // Legacy properties
          boolean tryUnsafe = false;
          if (SystemPropertyUtil.contains("io.netty.tryUnsafe")) {
              tryUnsafe = SystemPropertyUtil.getBoolean("io.netty.tryUnsafe", true);
          } else {
              tryUnsafe = SystemPropertyUtil.getBoolean("org.jboss.netty.tryUnsafe", true);
          }
  
          if (!tryUnsafe) {
              return false;
          }
  
          try {
              Class<?> unsafeClazz = Class.forName("sun.misc.Unsafe", true, loader);
              return hasUnsafeField(unsafeClazz);
          } catch (Exception e) {
              // Ignore
          }
  
          return false;
      }
  
      private static boolean hasUnsafeField(final Class<?> unsafeClass) throws PrivilegedActionException {
          return AccessController.doPrivileged(new PrivilegedExceptionAction<Boolean>() {
              public Boolean run() throws Exception {
                  unsafeClass.getDeclaredField("theUnsafe");
                  return true;
              }
          });
      }
  
      private static int javaVersion0() {
         try {
             // Check if its android, if so handle it the same way as java6.
             //
             // See https://github.com/netty/netty/issues/282
             Class.forName("android.app.Application");
             return 6;
         } catch (ClassNotFoundException e) {
             //Ignore
         }
 
         try {
             Class.forName(
                     "java.util.concurrent.LinkedTransferQueue", false,
                     BlockingQueue.class.getClassLoader());
             return 7;
         } catch (Exception e) {
             // Ignore
         }
 
         try {
             Class.forName(
                     "java.util.ArrayDeque", false, Queue.class.getClassLoader());
             return 6;
         } catch (Exception e) {
             // Ignore
         }
 
         return 5;
     }
 
     private DetectionUtil() {
         // only static method supported
     }
 }