/**
 * 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.hadoop.mrunit.mapreduce.mock;

import java.io.IOException;
import java.util.Iterator;
import java.util.List;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Counters;
import org.apache.hadoop.mapreduce.TaskAttemptID;
import org.apache.hadoop.mapreduce.TaskType;
import org.apache.hadoop.mapreduce.task.ReduceContextImpl;
import org.apache.hadoop.mrunit.mock.MockOutputCollector;
import org.apache.hadoop.mrunit.types.Pair;

public class MockReduceContext <KEYIN, VALUEIN, KEYOUT, VALUEOUT>
    extends ReduceContextImpl<KEYIN, VALUEIN, KEYOUT, VALUEOUT> {

  // The iterator over the input key, list(val).
  private Iterator<Pair<KEYIN, List<VALUEIN>>> inputIter;

  // The current key and list of values.
  private KEYIN curKey;
  private InspectableIterable curValueIterable;

  private MockOutputCollector<KEYOUT, VALUEOUT> output;

  /**
   * Create a new instance with the passed configuration, reducer key/values input 
   * pairs and counters
   * 
   * @param configuration Configuration for the mapper
   * @param in input key/value pairs for the mapper
   * @param counters pre-initialized counter values
   * 
   * @throws IOException
   * @throws InterruptedException
   */
  public MockReduceContext(Configuration configuration, 
                           final List<Pair<KEYIN, List<VALUEIN>>> in, 
                           final Counters counters) 
  throws IOException, InterruptedException {
    super(configuration,
          new TaskAttemptID("mrunit-jt", 0, TaskType.REDUCE, 0, 0),
          new MockRawKeyValueIterator(), null, null, null,
          new MockOutputCommitter(), new MockReporter(counters), null,
          (Class) Text.class, (Class) Text.class);
    this.inputIter = in.iterator();
    this.output = new MockOutputCollector<KEYOUT, VALUEOUT>();
  }
  
  /**
   * Create a new instance with the passed reducer key/values input pairs and
   * counters. A new {@link Configuration} object will be created and used
   * to configure the reducer
   * 
   * @param in input key/values pairs for the reducer
   * @param counters pre-initialized counter values
   */
  public MockReduceContext(final List<Pair<KEYIN, List<VALUEIN>>> in, 
          final Counters counters) 
  throws IOException, InterruptedException {
    this(new Configuration(), in, counters);
  }

  /**
   * A private iterable/iterator implementation that wraps around the 
   * underlying iterable/iterator used by the input value list. This
   * memorizes the last value we saw so that we can return it in getCurrentValue().
   */
  private class InspectableIterable implements Iterable<VALUEIN> {
    private Iterable<VALUEIN> base;
    private VALUEIN lastVal;
    private boolean used; // if true, don't re-iterate.

    public InspectableIterable(final Iterable<VALUEIN> baseCollection) {
      this.base = baseCollection;
    }

    public Iterator<VALUEIN> iterator() {
      if (used) {
        return new NullIterator();
      } else {
        used = true;
        return new InspectableIterator(this.base.iterator());
      }
    }

    public VALUEIN getLastVal() {
      return lastVal;
    }

    private class NullIterator
        extends ReduceContextImpl<KEYIN, VALUEIN, KEYOUT, VALUEOUT>.ValueIterator
        implements Iterator<VALUEIN> {
      public VALUEIN next() {
        return null;
      }

      public boolean hasNext() {
        return false;
      }

      public void remove() {
      }
    }

    private class InspectableIterator
        extends ReduceContextImpl<KEYIN, VALUEIN, KEYOUT, VALUEOUT>.ValueIterator
        implements Iterator<VALUEIN> {
      private Iterator<VALUEIN> iter;
      public InspectableIterator(final Iterator<VALUEIN> baseIter) {
        iter = baseIter;
      }

      public VALUEIN next() {
        InspectableIterable.this.lastVal = iter.next();
        return InspectableIterable.this.lastVal;
      }

      public boolean hasNext() {
        return iter.hasNext();
      }

      public void remove() {
        iter.remove();
      }
    }
  }

  @Override
  public boolean nextKey() {
    if (inputIter.hasNext()) {
      // Advance to the next key and list of values
      Pair<KEYIN, List<VALUEIN>> p = inputIter.next();
      curKey = p.getFirst();

      // Reset the value iterator
      curValueIterable = new InspectableIterable(p.getSecond());
      return true;
    } else {
      return false;
    }
  }

  @Override
  public boolean nextKeyValue() {
    return nextKey();
  }

  @Override
  public KEYIN getCurrentKey() {
    return curKey;
  }

  @Override
  public VALUEIN getCurrentValue() {
    return curValueIterable.getLastVal();
  }

  @Override
  public Iterable<VALUEIN> getValues() {
    return curValueIterable;
  }

  public void write(KEYOUT key, VALUEOUT value) throws IOException {
    output.collect(key, value);
  }

  @Override
  /** This method does nothing in the mock version. */
  public void progress() {
  }

  @Override
  /** This method does nothing in the mock version. */
  public void setStatus(String status) {
  }

  /**
   * @return the outputs from the MockOutputCollector back to
   * the test harness.
   */
  public List<Pair<KEYOUT, VALUEOUT>> getOutputs() {
    return output.getOutputs();
  }
}