code: /*
   * Copyright 2012-2018 Chronicle Map Contributors
   *
   * 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 net.openhft.chronicle.hash.serialization.impl;
  
  import net.openhft.chronicle.bytes.Byteable;
  import net.openhft.chronicle.bytes.BytesStore;
  import net.openhft.chronicle.bytes.RandomDataInput;
  import net.openhft.chronicle.core.Maths;
  import net.openhft.chronicle.hash.AbstractData;
  import net.openhft.chronicle.hash.Data;
  import net.openhft.chronicle.hash.serialization.DataAccess;
  import net.openhft.chronicle.values.Copyable;
  import net.openhft.chronicle.values.Values;
  import net.openhft.chronicle.wire.WireIn;
  import net.openhft.chronicle.wire.WireOut;
  import org.jetbrains.annotations.NotNull;
  import org.jetbrains.annotations.Nullable;
  
  import java.nio.ByteBuffer;
  
  public class ValueDataAccess<T> extends AbstractData<T> implements DataAccess<T> {
  
      /**
       * Config field
       */
      private Class<T> valueType;
  
      // Cache fields
      private transient Class<? extends T> nativeClass;
      private transient Class<? extends T> heapClass;
      private transient Byteable nativeInstance;
      private transient Copyable nativeInstanceAsCopyable;
  
      /**
       * State field
       */
      private transient Byteable instance;
  
      public ValueDataAccess(Class<T> valueType) {
          this.valueType = valueType;
          initTransients();
      }
  
      /**
       * Returns the interface of values serialized.
       */
      protected Class<T> valueType() {
          return valueType;
      }
  
      protected Class<? extends T> nativeClass() {
          return nativeClass;
      }
  
      protected Class<? extends T> heapClass() {
          return heapClass;
      }
  
      private void initTransients() {
          nativeInstance = (Byteable) Values.newNativeReference(valueType);
          nativeInstanceAsCopyable = (Copyable) nativeInstance;
          nativeClass = (Class<? extends T>) nativeInstance.getClass();
          heapClass = Values.heapClassFor(valueType);
          nativeInstance.bytesStore(allocateBytesStoreForInstance(), 0, nativeInstance.maxSize());
      }
  
      private BytesStore allocateBytesStoreForInstance() {
          long instanceSize = nativeInstance.maxSize();
          if (instanceSize > 0x7FFFFFF0) {
              return BytesStore.nativeStoreWithFixedCapacity(instanceSize);
          } else {
              return BytesStore.wrap(ByteBuffer.allocate(Maths.toUInt31(instanceSize)));
          }
      }
  
      protected T createInstance() {
          try {
              return heapClass.newInstance();
          } catch (InstantiationException | IllegalAccessException e) {
              throw new RuntimeException(e);
          }
      }
  
      @Override
      public RandomDataInput bytes() {
          return instance.bytesStore();
      }
  
      @Override
      public long offset() {
          return instance.offset();
      }
  
      @Override
      public long size() {
          return instance.maxSize();
      }
  
      @Override
      public T get() {
          return (T) instance;
      }
  
      @Override
      public T getUsing(@Nullable T using) {
          if (using == null)
              using = createInstance();
          ((Copyable) using).copyFrom(instance);
          return using;
      }
  
      @Override
      public Data<T> getData(@NotNull T instance) {
          if (instance.getClass() == nativeClass) {
              this.instance = (Byteable) instance;
          } else {
              nativeInstanceAsCopyable.copyFrom(instance);
              this.instance = nativeInstance;
          }
          return this;
      }
  
      @Override
      public void uninit() {
          instance = null;
      }
  
      @Override
      public DataAccess<T> copy() {
          return new ValueDataAccess<>(valueType);
      }
  
      @Override
      public void readMarshallable(@NotNull WireIn wireIn) {
          valueType = wireIn.read("valueType").typeLiteral();
          initTransients();
      }
  
      @Override
      public void writeMarshallable(@NotNull WireOut wireOut) {
          wireOut.write("valueType").typeLiteral(valueType);
      }
  }
  