/**
 * 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.mapred.lib;

import java.io.IOException;
import java.util.ArrayList;

import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileStatus;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapred.FileInputFormat;
import org.apache.hadoop.mapred.FileSplit;
import org.apache.hadoop.mapred.InputSplit;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.JobConfigurable;
import org.apache.hadoop.mapred.LineRecordReader;
import org.apache.hadoop.mapred.RecordReader;
import org.apache.hadoop.mapred.Reporter;
import org.apache.hadoop.util.LineReader;

/**
 * NLineInputFormat which splits N lines of input as one split.
 * 
 * In many "pleasantly" parallel applications, each process/mapper processes the
 * same input file (s), but with computations are controlled by different
 * parameters.(Referred to as "parameter sweeps"). One way to achieve this, is
 * to specify a set of parameters (one set per line) as input in a control file
 * (which is the input path to the map-reduce application, where as the input
 * dataset is specified via a config variable in JobConf.).
 * 
 * The NLineInputFormat can be used in such applications, that splits the input
 * file such that by default, one line is fed as a value to one map task, and
 * key is the offset. i.e. (k,v) is (LongWritable, Text). The location hints
 * will span the whole mapred cluster.
 */

public class NLineInputFormat extends FileInputFormat<LongWritable, Text>
		implements JobConfigurable {
	private int N = 1;

	public RecordReader<LongWritable, Text> getRecordReader(
			InputSplit genericSplit, JobConf job, Reporter reporter)
			throws IOException {
		reporter.setStatus(genericSplit.toString());
		return new LineRecordReader(job, (FileSplit) genericSplit);
	}

	/**
	 * Logically splits the set of input files for the job, splits N lines of
	 * the input as one split.
	 * 
	 * @see org.apache.hadoop.mapred.FileInputFormat#getSplits(JobConf, int)
	 */
	public InputSplit[] getSplits(JobConf job, int numSplits)
			throws IOException {
		ArrayList<FileSplit> splits = new ArrayList<FileSplit>();
		for (FileStatus status : listStatus(job)) {
			Path fileName = status.getPath();
			if (status.isDir()) {
				throw new IOException("Not a file: " + fileName);
			}
			FileSystem fs = fileName.getFileSystem(job);
			LineReader lr = null;
			try {
				FSDataInputStream in = fs.open(fileName);
				lr = new LineReader(in, job);
				Text line = new Text();
				int numLines = 0;
				long begin = 0;
				long length = 0;
				int num = -1;
				while ((num = lr.readLine(line)) > 0) {
					numLines++;
					length += num;
					if (numLines == N) {
						splits.add(new FileSplit(fileName, begin, length,
								new String[] {}));
						begin += length;
						length = 0;
						numLines = 0;
					}
				}
				if (numLines != 0) {
					splits.add(new FileSplit(fileName, begin, length,
							new String[] {}));
				}

			} finally {
				if (lr != null) {
					lr.close();
				}
			}
		}
		return splits.toArray(new FileSplit[splits.size()]);
	}

	public void configure(JobConf conf) {
		N = conf.getInt("mapred.line.input.format.linespermap", 1);
	}
}
