/*
 * 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.flink.hadoopcompatibility.mapred;

import org.apache.flink.annotation.Public;
import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.api.common.functions.OpenContext;
import org.apache.flink.api.common.functions.RichGroupReduceFunction;
import org.apache.flink.api.common.typeinfo.TypeInformation;
import org.apache.flink.api.common.typeutils.TypeSerializer;
import org.apache.flink.api.java.hadoop.mapred.wrapper.HadoopDummyReporter;
import org.apache.flink.api.java.tuple.Tuple2;
import org.apache.flink.api.java.typeutils.ResultTypeQueryable;
import org.apache.flink.api.java.typeutils.TupleTypeInfo;
import org.apache.flink.api.java.typeutils.TypeExtractor;
import org.apache.flink.hadoopcompatibility.mapred.wrapper.HadoopOutputCollector;
import org.apache.flink.hadoopcompatibility.mapred.wrapper.HadoopTupleUnwrappingIterator;
import org.apache.flink.util.Collector;
import org.apache.flink.util.InstantiationUtil;

import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.Reducer;
import org.apache.hadoop.mapred.Reporter;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;

/**
 * This wrapper maps a Hadoop Reducer (mapred API) to a non-combinable Flink GroupReduceFunction.
 */
@SuppressWarnings("rawtypes")
@Public
public final class HadoopReduceFunction<KEYIN, VALUEIN, KEYOUT, VALUEOUT>
        extends RichGroupReduceFunction<Tuple2<KEYIN, VALUEIN>, Tuple2<KEYOUT, VALUEOUT>>
        implements ResultTypeQueryable<Tuple2<KEYOUT, VALUEOUT>>, Serializable {

    private static final long serialVersionUID = 1L;

    private transient Reducer<KEYIN, VALUEIN, KEYOUT, VALUEOUT> reducer;
    private transient JobConf jobConf;

    private transient HadoopTupleUnwrappingIterator<KEYIN, VALUEIN> valueIterator;
    private transient HadoopOutputCollector<KEYOUT, VALUEOUT> reduceCollector;
    private transient Reporter reporter;

    /**
     * Maps a Hadoop Reducer (mapred API) to a non-combinable Flink GroupReduceFunction.
     *
     * @param hadoopReducer The Hadoop Reducer to wrap.
     */
    public HadoopReduceFunction(Reducer<KEYIN, VALUEIN, KEYOUT, VALUEOUT> hadoopReducer) {
        this(hadoopReducer, new JobConf());
    }

    /**
     * Maps a Hadoop Reducer (mapred API) to a non-combinable Flink GroupReduceFunction.
     *
     * @param hadoopReducer The Hadoop Reducer to wrap.
     * @param conf The JobConf that is used to configure the Hadoop Reducer.
     */
    public HadoopReduceFunction(
            Reducer<KEYIN, VALUEIN, KEYOUT, VALUEOUT> hadoopReducer, JobConf conf) {
        if (hadoopReducer == null) {
            throw new NullPointerException("Reducer may not be null.");
        }
        if (conf == null) {
            throw new NullPointerException("JobConf may not be null.");
        }

        this.reducer = hadoopReducer;
        this.jobConf = conf;
    }

    @SuppressWarnings("unchecked")
    @PublicEvolving
    @Override
    public void open(OpenContext openContext) throws Exception {
        super.open(openContext);
        this.reducer.configure(jobConf);

        this.reporter = new HadoopDummyReporter();
        this.reduceCollector = new HadoopOutputCollector<KEYOUT, VALUEOUT>();
        Class<KEYIN> inKeyClass =
                (Class<KEYIN>) TypeExtractor.getParameterType(Reducer.class, reducer.getClass(), 0);
        TypeSerializer<KEYIN> keySerializer =
                getRuntimeContext().createSerializer(TypeExtractor.getForClass(inKeyClass));
        this.valueIterator = new HadoopTupleUnwrappingIterator<KEYIN, VALUEIN>(keySerializer);
    }

    @Override
    public void reduce(
            final Iterable<Tuple2<KEYIN, VALUEIN>> values,
            final Collector<Tuple2<KEYOUT, VALUEOUT>> out)
            throws Exception {

        reduceCollector.setFlinkCollector(out);
        valueIterator.set(values.iterator());
        reducer.reduce(valueIterator.getCurrentKey(), valueIterator, reduceCollector, reporter);
    }

    @SuppressWarnings("unchecked")
    @Override
    public TypeInformation<Tuple2<KEYOUT, VALUEOUT>> getProducedType() {
        Class<KEYOUT> outKeyClass =
                (Class<KEYOUT>)
                        TypeExtractor.getParameterType(Reducer.class, reducer.getClass(), 2);
        Class<VALUEOUT> outValClass =
                (Class<VALUEOUT>)
                        TypeExtractor.getParameterType(Reducer.class, reducer.getClass(), 3);

        final TypeInformation<KEYOUT> keyTypeInfo =
                TypeExtractor.getForClass((Class<KEYOUT>) outKeyClass);
        final TypeInformation<VALUEOUT> valueTypleInfo =
                TypeExtractor.getForClass((Class<VALUEOUT>) outValClass);
        return new TupleTypeInfo<Tuple2<KEYOUT, VALUEOUT>>(keyTypeInfo, valueTypleInfo);
    }

    /**
     * Custom serialization methods.
     *
     * @see <a
     *     href="http://docs.oracle.com/javase/7/docs/api/java/io/Serializable.html">http://docs.oracle.com/javase/7/docs/api/java/io/Serializable.html</a>
     */
    private void writeObject(final ObjectOutputStream out) throws IOException {

        out.writeObject(reducer.getClass());
        jobConf.write(out);
    }

    @SuppressWarnings("unchecked")
    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {

        Class<Reducer<KEYIN, VALUEIN, KEYOUT, VALUEOUT>> reducerClass =
                (Class<Reducer<KEYIN, VALUEIN, KEYOUT, VALUEOUT>>) in.readObject();
        reducer = InstantiationUtil.instantiate(reducerClass);

        jobConf = new JobConf();
        jobConf.readFields(in);
    }
}
