/*
    * 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.IOException;
  import java.util.Iterator;
  import org.apache.hadoop.io.Writable;
  
  /**
   * This iterator is designed to deserialize a byte array on the fly to
   * provide new copies of writable objects when desired.  It does not reuse
   * objects, and instead creates a new one for every next().
   *
   * @param <T> Type that extends Writable that will be iterated
   */
  public abstract class ByteStructIterator<T extends Writable> implements
      Iterator<T> {
    /** Data input */
    protected final ExtendedDataInput extendedDataInput;
  
    /**
     * Wrap ExtendedDataInput in ByteArrayIterator
     *
     * @param extendedDataInput ExtendedDataInput
     */
    public ByteStructIterator(ExtendedDataInput extendedDataInput) {
      this.extendedDataInput = extendedDataInput;
    }
  
    @Override
    public boolean hasNext() {
      return !extendedDataInput.endOfInput();
    }
  
    @Override
    public T next() {
      T writable = createWritable();
      try {
        writable.readFields(extendedDataInput);
      } catch (IOException e) {
        throw new IllegalStateException("next: readFields got IOException", e);
      }
      return writable;
    }
  
    @Override
    public void remove() {
      throw new UnsupportedOperationException("remove: Not supported");
    }
  
    /**
     * Must be able to create the writable object
     *
     * @return New writable
     */
    protected abstract T createWritable();
  }