/*
    * 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.tuple;
  
  import java.io.DataInput;
  import java.io.DataOutput;
  import java.io.IOException;
  
  import org.apache.commons.lang3.tuple.Pair;
  import org.apache.hadoop.io.Writable;
  
  /**
   * Pair Writable class, that knows types upfront and can deserialize itself.
   *
   * PairWritable knows types, as instances are passed through constructor, and
   * are references are immutable (values themselves are mutable).
   *
   * Child classes specify no-arg constructor that passes concrete types in.
   *
   * Extends Pair, not ImmutablePair, since later class is final. Code is
   * copied from it.
   *
   * @param <L> Type of the left element
   * @param <R> Type of the right element
   */
  public class PairWritable<L extends Writable, R extends Writable>
      extends Pair<L, R> implements Writable {
    /** Left object */
    private final L left;
    /** Right object */
    private final R right;
  
    /**
     * Create a new pair instance.
     *
     * @param left  the left value
     * @param right  the right value
     */
    public PairWritable(L left, R right) {
      this.left = left;
      this.right = right;
    }
  
    /**
     * <p>
     * Obtains an immutable pair of from two objects inferring
     * the generic types.</p>
     *
     * <p>This factory allows the pair to be created using inference to
     * obtain the generic types.</p>
     *
     * @param <L> the left element type
     * @param <R> the right element type
     * @param left  the left element, may be null
     * @param right  the right element, may be null
     * @return a pair formed from the two parameters, not null
     */
    public static <L extends Writable, R extends Writable>
    PairWritable<L, R> of(L left, R right) {
      return new PairWritable<L, R>(left, right);
    }
  
    @Override
    public final L getLeft() {
      return left;
    }
  
    @Override
    public final R getRight() {
      return right;
    }
  
    /**
     * <p>Throws {@code UnsupportedOperationException}.</p>
     *
     * <p>This pair is immutable, so this operation is not supported.</p>
     *
     * @param value  the value to set
     * @return never
     * @throws UnsupportedOperationException as this operation is not supported
     */
    @Override
    public final R setValue(R value) {
      throw new UnsupportedOperationException();
   }
 
   @Override
   public final void write(DataOutput out) throws IOException {
     left.write(out);
     right.write(out);
   }
 
   @Override
   public final void readFields(DataInput in) throws IOException {
     left.readFields(in);
     right.readFields(in);
   }
 }