/*
    * 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 org.apache.hadoop.io.Writable;
  import org.apache.hadoop.io.WritableComparable;
  
  import java.io.IOException;
  
  /**
   * VertexIdData iterator for
   * {@link ByteArrayOneMessageToManyIds}
   *
   * @param <I> vertexId type
   * @param <M> message type
   */
  public class OneMessageToManyIdsIterator<I extends WritableComparable,
      M extends Writable> implements VertexIdMessageIterator<I, M> {
    /** VertexIdMessages object to iterate over */
    private final ByteArrayOneMessageToManyIds<I, M> vertexIdMessages;
    /** Reader of the serialized edges */
    private final ExtendedDataInput extendedDataInput;
  
    /** Current vertex Id*/
    private I vertexId;
    /** Current message */
    private M msg;
    /** Counts of ids left to read before next message */
    private int idsToRead = 0;
    /** Size of message read */
    private int msgSize = 0;
    /** Is current message newly read */
    private boolean newMessage;
  
    /**
     * Constructor
     *
     * @param vertexIdMessages vertexId messages object to iterate over
     */
    public OneMessageToManyIdsIterator(
        final ByteArrayOneMessageToManyIds<I, M> vertexIdMessages) {
      this.vertexIdMessages = vertexIdMessages;
      this.extendedDataInput = vertexIdMessages.getConf()
          .createExtendedDataInput(vertexIdMessages.extendedDataOutput);
    }
  
    @Override
    public I getCurrentVertexId() {
      return vertexId;
    }
  
    @Override
    public M getCurrentMessage() {
      return getCurrentData();
    }
  
    @Override
    public M getCurrentData() {
      return msg;
    }
  
    @Override
    public M releaseCurrentData() {
      M releasedData = msg;
      msg = null;
      return releasedData;
    }
  
    @Override
    public I releaseCurrentVertexId() {
      I releasedVertexId = vertexId;
      vertexId = null;
      return releasedVertexId;
    }
  
    @Override
    public boolean hasNext() {
      return extendedDataInput.available() > 0;
    }
  
    /**
     * Properly initialize vertexId & msg object before calling next()
     */
   private void initialize() {
     if (vertexId == null) {
       vertexId = vertexIdMessages.getConf().createVertexId();
     }
     if (msg == null) {
       msg = vertexIdMessages.createData();
     }
   }
 
   @Override
   public void next() {
     initialize();
     try {
       if (idsToRead == 0) {
         newMessage = true; // a new message is read
         int initial = extendedDataInput.getPos();
         msg.readFields(extendedDataInput);
         msgSize = extendedDataInput.getPos() - initial;
         idsToRead = extendedDataInput.readInt();
       } else {
         newMessage = false; // same as previous message
       }
       vertexId.readFields(extendedDataInput);
       idsToRead -= 1;
     } catch (IOException e) {
       throw new IllegalStateException("next: IOException", e);
     }
   }
 
   @Override
   public int getCurrentMessageSize() {
     return getCurrentDataSize();
   }
 
   @Override
   public int getCurrentDataSize() {
     return msgSize;
   }
 
   @Override
   public boolean isNewMessage() {
     return newMessage;
   }
 }