/*
    * Copyright 2016 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:
    *
    *   https://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 io.netty.handler.codec.compression;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.util.ByteProcessor;
  import io.netty.util.internal.ObjectUtil;
  import io.netty.util.internal.PlatformDependent;
  
  import java.lang.reflect.Method;
  import java.nio.ByteBuffer;
  import java.util.zip.Adler32;
  import java.util.zip.CRC32;
  import java.util.zip.Checksum;
  
  /**
   * {@link Checksum} implementation which can directly act on a {@link ByteBuf}.
   *
   * Implementations may optimize access patterns depending on if the {@link ByteBuf} is backed by a
   * byte array ({@link ByteBuf#hasArray()} is {@code true}) or not.
   */
  abstract class ByteBufChecksum implements Checksum {
  
      /**
       * on OpenJDK Adler32 and CRC32 both calls ZipUtils.loadLibrary on class init.
       */
      private static class ZlibChecksumMethods {
          private static final Method ADLER32_UPDATE_METHOD;
          private static final Method CRC32_UPDATE_METHOD;
  
          static {
              // See if we can use fast-path when using ByteBuf that is not heap based as Adler32 and CRC32 added support
              // for update(ByteBuffer) in JDK8.
              ADLER32_UPDATE_METHOD = updateByteBuffer(new Adler32());
              CRC32_UPDATE_METHOD = updateByteBuffer(new CRC32());
          }
      }
  
      private final ByteProcessor updateProcessor = new ByteProcessor() {
          @Override
          public boolean process(byte value) throws Exception {
              update(value);
              return true;
          }
      };
  
      private static Method updateByteBuffer(Checksum checksum) {
          if (PlatformDependent.javaVersion() >= 8) {
              try {
                  Method method = checksum.getClass().getDeclaredMethod("update", ByteBuffer.class);
                  method.invoke(checksum, ByteBuffer.allocate(1));
                  return method;
              } catch (Throwable ignore) {
                  return null;
              }
          }
          return null;
      }
  
      static ByteBufChecksum wrapChecksum(Checksum checksum) {
          ObjectUtil.checkNotNull(checksum, "checksum");
          if (checksum instanceof ByteBufChecksum) {
              return (ByteBufChecksum) checksum;
          }
          if (checksum instanceof Adler32 && ZlibChecksumMethods.ADLER32_UPDATE_METHOD != null) {
              return new ReflectiveByteBufChecksum(checksum, ZlibChecksumMethods.ADLER32_UPDATE_METHOD);
          }
          if (checksum instanceof CRC32 && ZlibChecksumMethods.CRC32_UPDATE_METHOD != null) {
              return new ReflectiveByteBufChecksum(checksum, ZlibChecksumMethods.CRC32_UPDATE_METHOD);
          }
          return new SlowByteBufChecksum(checksum);
      }
  
      /**
       * @see #update(byte[], int, int)
       */
      public void update(ByteBuf b, int off, int len) {
          if (b.hasArray()) {
              update(b.array(), b.arrayOffset() + off, len);
          } else {
              b.forEachByte(off, len, updateProcessor);
          }
      }
  
      private static final class ReflectiveByteBufChecksum extends SlowByteBufChecksum {
          private final Method method;
 
         ReflectiveByteBufChecksum(Checksum checksum, Method method) {
             super(checksum);
             this.method = method;
         }
 
         @Override
         public void update(ByteBuf b, int off, int len) {
             if (b.hasArray()) {
                 update(b.array(), b.arrayOffset() + off, len);
             } else {
                 try {
                     method.invoke(checksum, CompressionUtil.safeNioBuffer(b, off, len));
                 } catch (Throwable cause) {
                     throw new Error();
                 }
             }
         }
     }
 
     private static class SlowByteBufChecksum extends ByteBufChecksum {
 
         protected final Checksum checksum;
 
         SlowByteBufChecksum(Checksum checksum) {
             this.checksum = checksum;
         }
 
         @Override
         public void update(int b) {
             checksum.update(b);
         }
 
         @Override
         public void update(byte[] b, int off, int len) {
             checksum.update(b, off, len);
         }
 
         @Override
         public long getValue() {
             return checksum.getValue();
         }
 
         @Override
         public void reset() {
             checksum.reset();
         }
     }
 }