/*
 * 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.solr.client.solrj.io.ops;

import java.io.IOException;
import java.util.UUID;

import org.apache.solr.client.solrj.io.Tuple;
import org.apache.solr.client.solrj.io.stream.expr.Explanation;
import org.apache.solr.client.solrj.io.stream.expr.Explanation.ExpressionType;
import org.apache.solr.client.solrj.io.stream.expr.StreamExpression;
import org.apache.solr.client.solrj.io.stream.expr.StreamExpressionParameter;
import org.apache.solr.client.solrj.io.stream.expr.StreamFactory;

public class DistinctOperation implements ReduceOperation {

  private static final long serialVersionUID = 1L;
  private UUID operationNodeId = UUID.randomUUID();
  private Tuple current;

  public DistinctOperation(StreamExpression expression, StreamFactory factory) throws IOException {
    init();
  }

  public DistinctOperation() {
    init();
  }

  private void init() {
  }

  public StreamExpressionParameter toExpression(StreamFactory factory) throws IOException {
    StreamExpression expression = new StreamExpression(factory.getFunctionName(this.getClass()));
    return expression;
  }

  @Override
  public Explanation toExplanation(StreamFactory factory) throws IOException {
    return new Explanation(operationNodeId.toString())
      .withExpressionType(ExpressionType.OPERATION)
      .withFunctionName(factory.getFunctionName(getClass()))
      .withImplementingClass(getClass().getName())
      .withExpression(toExpression(factory).toString());
  }

  public Tuple reduce() {
    // Return the tuple after setting current to null. This will ensure the next call to 
    // operate stores that tuple
    Tuple toReturn = current;
    current = null;
    
    return toReturn;
  }

  public void operate(Tuple tuple) {
    // we only care about the first one seen. Drop all but the first
    if(null == current){
      current = tuple;
    }
  }
}