/*
    * This file is part of Waarp Project (named also Waarp or GG).
    *
    *  Copyright (c) 2019, Waarp SAS, and individual contributors by the @author
    *  tags. See the COPYRIGHT.txt in the distribution for a full listing of
    * individual contributors.
    *
    *  All Waarp Project is free software: you can redistribute it and/or
    * modify it under the terms of the GNU General Public License as published by
   * the Free Software Foundation, either version 3 of the License, or (at your
   * option) any later version.
   *
   * Waarp is distributed in the hope that it will be useful, but WITHOUT ANY
   * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
   * A PARTICULAR PURPOSE. See the GNU General Public License for more details.
   *
   *  You should have received a copy of the GNU General Public License along with
   * Waarp . If not, see <http://www.gnu.org/licenses/>.
   */
  
  /*
   * Licensed 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.waarp.compress.zstdunsafe;
  
  import org.waarp.compress.IncompatibleJvmException;
  import sun.misc.Unsafe;
  
  import java.lang.reflect.Field;
  import java.nio.Buffer;
  import java.nio.ByteOrder;
  
  import static java.lang.String.*;
  
  public final class UnsafeUtil {
    private static boolean initialized;
    public static final Unsafe UNSAFE;
    private static final long ADDRESS_OFFSET;
  
    private UnsafeUtil() {
    }
  
    static {
      Unsafe tempUnsafe = null;
      long tempField = 0;
      try {
        initLittleEndian();
        tempUnsafe = initUnsafe();
        tempField = initAccessor();
        initialized = true;
      } catch (final Exception e) {
        initialized = false;
      }
      UNSAFE = tempUnsafe;
      ADDRESS_OFFSET = tempField;
    }
  
    public static boolean isValid() {
      return initialized;
    }
  
    /**
     * @throws IncompatibleJvmException if this implementation is not available
     */
    private static final void initLittleEndian() {
      if (initialized) {
        return;
      }
      final ByteOrder order = ByteOrder.nativeOrder();
      if (!order.equals(ByteOrder.LITTLE_ENDIAN)) {
        throw new IncompatibleJvmException(
            format("Zstandard requires a little endian platform (found %s)",
                   order));
      }
    }
  
    /**
     * @throws IncompatibleJvmException if this implementation is not available
     */
    private static final Unsafe initUnsafe() {
      if (initialized) {
        return UNSAFE;
      }
      try {
        final Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");
        theUnsafe.setAccessible(true);
        return (Unsafe) theUnsafe.get(null);
      } catch (final Exception e) {
        throw new IncompatibleJvmException(
           "Zstandard requires access to sun.misc.Unsafe");
     }
   }
 
   /**
    * @throws IncompatibleJvmException if this implementation is not available
    */
   private static final long initAccessor() {
     if (initialized) {
       return ADDRESS_OFFSET;
     }
     try {
       // Remove warning
       final Class cls =
           Class.forName("jdk.internal.module.IllegalAccessLogger");
       final Field logger = cls.getDeclaredField("logger");
       UNSAFE.putObjectVolatile(cls, UNSAFE.staticFieldOffset(logger), null);
 
       // fetch the address field for direct buffers
       return UNSAFE.objectFieldOffset(Buffer.class.getDeclaredField("address"));
     } catch (final Exception e) {
       throw new IncompatibleJvmException(
           "Zstandard requires access to java.nio.Buffer raw address field");
     }
   }
 
   public static final long getAddress(final Buffer buffer) {
     if (!buffer.isDirect()) {
       throw new IllegalArgumentException("buffer is not direct");
     }
     return UNSAFE.getLong(buffer, ADDRESS_OFFSET);
   }
 }