/**
 * 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.streaming;

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.util.Iterator;
import java.net.URLDecoder;

import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.Reducer;
import org.apache.hadoop.mapred.Mapper;
import org.apache.hadoop.mapred.Reducer;
import org.apache.hadoop.mapred.Reporter;
import org.apache.hadoop.mapred.OutputCollector;
import org.apache.hadoop.util.StringUtils;
import org.apache.hadoop.util.ReflectionUtils;

import org.apache.hadoop.io.WritableComparable;
import org.apache.hadoop.io.Writable;

/** A generic Reducer bridge.
 *  It delegates operations to an external program via stdin and stdout.
 */
public class PipeReducer extends PipeMapRed implements 
Reducer<WritableComparable, Writable, WritableComparable, Writable> {

  protected Reducer preReducer;
  protected BufferingOutputCollector oc;
  private boolean ignoreKey = false;

  String getPipeCommand(JobConf job) {
    String str = job.get("stream.reduce.streamprocessor");
    if (str == null) {
      return str;
    }
    try {
      return URLDecoder.decode(str, "UTF-8");
    } catch (UnsupportedEncodingException e) {
      System.err.println("stream.reduce.streamprocessor in jobconf not found");
      return null;
    }
  }

  public void configure(JobConf job) {
      super.configure(job);
      Class<?> c = job.getClass("stream.reduce.posthook", null, Mapper.class);
      if(c != null) {
          postMapper = (Mapper)ReflectionUtils.newInstance(c, job);
          LOG.info("PostHook="+c.getName());
      }

      c = job.getClass("stream.reduce.prehook", null, Reducer.class);
      if(c != null) {
          preReducer = (Reducer)ReflectionUtils.newInstance(c, job);
          oc = new InmemBufferingOutputCollector();
          LOG.info("PreHook="+c.getName());
      }
      this.ignoreKey = job.getBoolean("stream.reduce.ignoreKey", false);
  }

  boolean getDoPipe() {
    String argv = getPipeCommand(job_);
    // Currently: null is identity reduce. REDUCE_NONE is no-map-outputs.
    return (argv != null) && !StreamJob.REDUCE_NONE.equals(argv);
  }

    private void blowPipe(WritableComparable key, Writable val, OutputCollector output) throws IOException {
        numRecRead_++;
        maybeLogRecord();

        // i took out the check for doPipe_. it's ridiculous.
        // doPipes is set under conditions where the reducer is 
        // IdentityReducer. so the code would never come through this
        // path.
        if (outerrThreadsThrowable != null) {
            mapRedFinished();
            throw new IOException ("MROutput/MRErrThread failed:"
                                   + StringUtils.stringifyException(outerrThreadsThrowable));
        }
        if(!this.ignoreKey) {
            write(key);
            clientOut_.write('\t');
        }
        write(val);
        clientOut_.write('\n');
        //        clientOut_.flush();
    }

  public void reduce(WritableComparable key, Iterator values, OutputCollector output,
                     Reporter reporter) throws IOException {

    Writable [] prret;
    Writable val;

    // init
    if (doPipe_ && outThread_ == null) {
      startOutputThreads(output, reporter);
    }
    try {
      if (preReducer != null) {
          preReducer.reduce(key, values, oc, reporter);
          while((prret = oc.retrieve()) != null) {
              key = (WritableComparable)prret[0];
              val = prret[1];
              blowPipe(key, val, output);
          }
      } else {
          while (values.hasNext()) {
              val = (Writable) values.next();
              blowPipe(key, val, output);
          }
      }
    } catch (IOException io) {
      // a common reason to get here is failure of the subprocess.
      // Document that fact, if possible.
      String extraInfo = "";
      try {
        int exitVal = sim.exitValue();
	if (exitVal == 0) {
	  extraInfo = "subprocess exited successfully\n";
	} else {
	  extraInfo = "subprocess exited with error code " + exitVal + "\n";
	};
      } catch (IllegalThreadStateException e) {
        // hmm, but child is still running.  go figure.
	extraInfo = "subprocess still running\n";
      };
      appendLogToJobLog("failure");
      mapRedFinished();
      throw new IOException(extraInfo + getContext() + io.getMessage());
    }
  }

  public void close() throws IOException {
    if (preReducer != null) {
      preReducer.close();
    }
    appendLogToJobLog("success");
    mapRedFinished();
  }

  @Override
  char getFieldSeparator() {
    return super.reduceOutFieldSeparator;
  }

  @Override
  int getNumOfKeyFields() {
    return super.numOfReduceOutputKeyFields;
  }

}