/**
 * 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.mrql;

import java.io.*;
import java.util.Iterator;
import org.apache.hadoop.fs.*;
import org.apache.hadoop.io.*;
import org.apache.hama.bsp.*;
import org.apache.hama.HamaConfiguration;


/** A superclass for all MRQL FileInputFormats */
abstract public class BSPMRQLFileInputFormat extends FileInputFormat<MRContainer,MRContainer> implements MRQLFileInputFormat {
    public BSPMRQLFileInputFormat () {}

    /** record reader for map-reduce */
    abstract public RecordReader<MRContainer,MRContainer>
        getRecordReader ( InputSplit split, BSPJob job ) throws IOException;

    /** materialize the input file into a memory Bag */
    public Bag materialize ( final Path file ) throws IOException {
        final BSPJob job = new BSPJob((HamaConfiguration)Plan.conf,MRQLFileInputFormat.class);
        job.setInputPath(file);
        final InputSplit[] splits = getSplits(job,1);
        final RecordReader<MRContainer,MRContainer> rd = getRecordReader(splits[0],job);
        return new Bag(new BagIterator () {
                RecordReader<MRContainer,MRContainer> reader = rd;
                MRContainer key = reader.createKey();
                MRContainer value = reader.createKey();
                int i = 0;
                public boolean hasNext () {
                    try {
                        if (reader.next(key,value))
                            return true;
                        do {
                            if (++i >= splits.length)
                                return false;
                            reader.close();
                            reader = getRecordReader(splits[i],job);
                        } while (!reader.next(key,value));
                        return true;
                    } catch (IOException e) {
                        throw new Error("Cannot collect values from an intermediate result");
                    }
                }
                public MRData next () {
                    return value.data();
                }
            });
    }

    /** materialize the entire dataset into a Bag
     * @param x the DataSet in HDFS to collect values from
     * @param strip true if you want to stripout the source id (used in BSP sources)
     * @return the Bag that contains the collected values
     */
    public final Bag collect ( final DataSet x, boolean strip ) throws Exception {
        Bag res = new Bag();
        for ( DataSource s: x.source )
            if (s.to_be_merged)
                res = res.union(Plan.merge(s));
            else {
                Path path = new Path(s.path);
                final FileSystem fs = path.getFileSystem(Plan.conf);
                final FileStatus[] ds
                    = fs.listStatus(path,
                                    new PathFilter () {
                                        public boolean accept ( Path path ) {
                                            return !path.getName().startsWith("_");
                                        }
                                    });
                Bag b = new Bag();
                for ( FileStatus st: ds )
                    b = b.union(s.inputFormat.newInstance().materialize(st.getPath()));
                if (strip) {
                    // remove source_num
                    final Iterator<MRData> iter = b.iterator();
                    b = new Bag(new BagIterator() {
                            public boolean hasNext () {
                                return iter.hasNext();
                            }
                            public MRData next () {
                                return ((Tuple)iter.next()).get(1);
                            }
                        });
                };
                res = res.union(b);
            };
        return res;
    }
}