/*
    * 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.giraph.writable.kryo;
  
  import java.io.DataInput;
  import java.io.DataOutput;
  import java.io.IOException;
  
  import org.apache.giraph.utils.WritableUtils;
  import org.apache.hadoop.io.Writable;
  
  /**
   * Generic wrapper object, making any object writable.
   *
   * Uses Kryo inside for serialization.
   * Current configuration is not optimized for performance,
   * but Writable interface doesn't allow much room for it.
   *
   * Note - Java8 lambdas need to implement Serializable to work.
   *
   * @param <T> Object type
   */
  public class KryoWritableWrapper<T> implements Writable {
    /** Wrapped object */
    private T object;
  
    /**
     * Create wrapper given an object.
     * @param object Object instance
     */
    public KryoWritableWrapper(T object) {
      this.object = object;
    }
  
    /**
     * Creates wrapper initialized with null.
     */
    public KryoWritableWrapper() {
    }
  
    /**
     * Unwrap the object value
     * @return Object value
     */
    public T get() {
      return object;
    }
  
    /**
     * Set wrapped object value
     * @param object New object value
     */
    public void set(T object) {
      this.object = object;
    }
  
    @Override
    public void readFields(DataInput in) throws java.io.IOException {
      object = HadoopKryo.readClassAndObj(in);
    }
  
    @Override
    public void write(DataOutput out) throws IOException {
      HadoopKryo.writeClassAndObj(out, object);
    }
  
    /**
     * Returns Writable instance, wrapping given object only
     * if it is not already writable.
     *
     * @param object Object to potentially wrap
     * @return Writable object holding argument
     */
    public static Writable wrapIfNeeded(Object object) {
      if (object instanceof Writable) {
        return (Writable) object;
      } else {
        return new KryoWritableWrapper<>(object);
      }
    }
  
    /**
     * Unwrap Writable object if it was wrapped initially,
     * inverse of wrapIfNeeded function.
    * @param value Potentially wrapped value
    * @return Original unwrapped value
    * @param <T> Type of returned object.
    */
   public static <T> T unwrapIfNeeded(Writable value) {
     if (value instanceof KryoWritableWrapper) {
       return ((KryoWritableWrapper<T>) value).get();
     } else {
       return (T) value;
     }
   }
 
   /**
    * Wrap object with KryoWritableWrapper, create a writable copy of it,
    * and then unwrap it, allowing any object to be copied.
    *
    * @param object Object to copy
    * @return copy of the object
    * @param <T> Type of the object
    */
   public static <T> T wrapAndCopy(T object) {
     return WritableUtils.createCopy(new KryoWritableWrapper<>(object)).get();
   }
 
   /**
    * Converting the object to byte array.
    * @param object Object
    * @param <T> Type
    * @return byte array
    */
   public static <T> byte [] convertToByteArray(T object) {
     KryoWritableWrapper<T> wrapper =
             new KryoWritableWrapper<>(object);
     return WritableUtils.toByteArray(wrapper);
   }
 
   /**
    * Converting from byte array
    * @param arr byte array
    * @param <T> type
    * @return original object
    */
   public static <T> T convertFromByteArray(byte [] arr) {
     KryoWritableWrapper<T> wrapper =
             new KryoWritableWrapper<>();
     WritableUtils.fromByteArray(arr, wrapper);
     return wrapper.get();
   }
 }