/*
    * 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.chukwa.datacollection.writer;
  
  
  import java.util.List;
  import org.apache.hadoop.chukwa.Chunk;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.log4j.Logger;
  
  /**
   * A pipeline of Pipelineable writers
   * Controlled by option 'chukwaCollector.pipeline', which should be a comma-
   * separated list of classnames. 
   * 
   */
  public class PipelineStageWriter implements ChukwaWriter {
    Logger log = Logger.getLogger(PipelineStageWriter.class);
  
    ChukwaWriter writer; // head of pipeline
  
    @Override
    public CommitStatus add(List<Chunk> chunks) throws WriterException {
      return writer.add(chunks);
    }
  
    @Override
    public void close() throws WriterException {
      writer.close();
    }
  
    @Override
    public void init(Configuration conf) throws WriterException {
      if (conf.get("chukwaCollector.pipeline") != null) {
        String pipeline = conf.get("chukwaCollector.pipeline");
        try {
          String[] classes = pipeline.split(",");
          log.info("using pipelined writers, pipe length is " + classes.length);
          PipelineableWriter lastWriter = null;
          if (classes.length > 1) {
            lastWriter = (PipelineableWriter) conf.getClassByName(classes[0])
                .newInstance();
            lastWriter.init(conf);
            writer = lastWriter;
          }
  
          for (int i = 1; i < classes.length - 1; ++i) {
            Class<?> stageClass = conf.getClassByName(classes[i]);
            Object st = stageClass.newInstance();
            if (!(st instanceof PipelineableWriter))
              log.error("class " + classes[i]
                  + " in processing pipeline isn't a pipeline stage");
  
            PipelineableWriter stage = (PipelineableWriter) stageClass
                .newInstance();
            stage.init(conf);
            // throws exception if types don't match or class not found; this is
            // OK.
  
            lastWriter.setNextStage(stage);
            lastWriter = stage;
          }
          Class<?> stageClass = conf.getClassByName(classes[classes.length - 1]);
          Object st = stageClass.newInstance();
  
          if (!(st instanceof ChukwaWriter)) {
            log.error("class " + classes[classes.length - 1]
                + " at end of processing pipeline isn't a ChukwaWriter");
            throw new WriterException("bad pipeline");
          } else {
            ((ChukwaWriter)st).init(conf);
            if (lastWriter != null)
              lastWriter.setNextStage((ChukwaWriter) st);
            else
              writer = (ChukwaWriter) st; // one stage pipeline
          }
          return;
        } catch (Exception e) {
          // if anything went wrong (missing class, etc) we wind up here.
          log.error("failed to set up pipeline, defaulting to SeqFileWriter", e);
          // fall through to default case
          throw new WriterException("bad pipeline");
        }
     } else {
       throw new WriterException("must set chukwaCollector.pipeline");
     }
   }
 
 }