/*
    * 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.utils;
  
  import java.io.DataInput;
  import java.io.DataOutput;
  import java.io.IOException;
  import java.util.ArrayList;
  
  import org.apache.hadoop.conf.Configurable;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.io.Writable;
  import org.apache.hadoop.util.ReflectionUtils;
  
  /**
   * A Writable for ListArray containing instances of a class.
   *
   * @param <M> Message data
   */
  public abstract class ArrayListWritable<M extends Writable> extends ArrayList<M>
    implements Writable, Configurable {
    /** Defining a layout version for a serializable class. */
    private static final long serialVersionUID = 1L;
    /** Used for instantiation */
    private Class<M> refClass = null;
  
    /** Configuration */
    private Configuration conf;
  
    /**
     * Using the default constructor requires that the user implement
     * setClass(), guaranteed to be invoked prior to instantiation in
     * readFields()
     */
    public ArrayListWritable() {
    }
  
    /**
     * Constructor with another {@link ArrayListWritable}.
     *
     * @param arrayListWritable Array list to be used internally.
     */
    public ArrayListWritable(ArrayListWritable<M> arrayListWritable) {
      super(arrayListWritable);
    }
  
    /**
     * This constructor allows setting the refClass during construction.
     *
     * @param refClass internal type class
     */
    public ArrayListWritable(Class<M> refClass) {
      super();
      this.refClass = refClass;
    }
  
    /**
     * This is a one-time operation to set the class type
     *
     * @param refClass internal type class
     */
    public void setClass(Class<M> refClass) {
      if (this.refClass != null) {
        throw new RuntimeException(
            "setClass: refClass is already set to " +
                this.refClass.getName());
      }
      this.refClass = refClass;
    }
  
    /**
     * Subclasses must set the class type appropriately and can use
     * setClass(Class&lt;M&gt; refClass) to do it.
     */
    public abstract void setClass();
  
    @Override
    public void readFields(DataInput in) throws IOException {
      if (this.refClass == null) {
        setClass();
      }
  
      clear();                              // clear list before storing values
     int numValues = in.readInt();            // read number of values
     ensureCapacity(numValues);
     for (int i = 0; i < numValues; i++) {
       M value = ReflectionUtils.newInstance(refClass, conf);
       value.readFields(in);                // read a value
       add(value);                          // store it in values
     }
   }
 
   @Override
   public void write(DataOutput out) throws IOException {
     int numValues = size();
     out.writeInt(numValues);                 // write number of values
     for (int i = 0; i < numValues; i++) {
       get(i).write(out);
     }
   }
 
   @Override
   public final Configuration getConf() {
     return conf;
   }
 
   @Override
   public final void setConf(Configuration conf) {
     this.conf = conf;
   }
 }