/**
 * 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;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.charset.CharacterCodingException;
import java.security.DigestException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.regex.Pattern;
import java.util.regex.PatternSyntaxException;

import org.apache.hadoop.conf.Configurable;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.io.BytesWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.util.ReflectionUtils;

/**
 * A class that allows a map/red job to work on a sample of sequence files.
 * The sample is decided by the filter class set by the job.
 * 
 * @author hairong
 *
 */

public class SequenceFileInputFilter extends SequenceFileInputFormat {
    final private static String FILTER_CLASS = "sequencefile.filter.class";
    final private static String FILTER_FREQUENCY
                       = "sequencefile.filter.frequency";
    final private static String FILTER_REGEX = "sequencefile.filter.regex";
    
    public SequenceFileInputFilter() {
    }
    
    /** Create a record reader for the given split
     * @param split file split
     * @param job job configuration
     * @param reporter reporter who sends report to task tracker
     * @return RecordReader
     */
    public RecordReader getRecordReader(InputSplit split,
            JobConf job, Reporter reporter)
    throws IOException {
        
        reporter.setStatus(split.toString());
        
        return new FilterRecordReader(job, (FileSplit) split);
    }


    /** set the filter class
     * 
     * @param conf application configuration
     * @param filterClass filter class
     */
    public static void setFilterClass(Configuration conf, Class filterClass) {
        conf.set(FILTER_CLASS, filterClass.getName() );
    }

         
    /**
     * filter interface
     */
    public interface Filter extends Configurable {
        /** filter function
         * Decide if a record should be filtered or not
         * @param key record key
         * @return true if a record is accepted; return false otherwise
         */
        public abstract boolean accept(Writable key);
    }
    
    /**
     * base calss for Filters
     */
    public static abstract class FilterBase implements Filter {
        Configuration conf;
        
        public Configuration getConf() {
            return conf;
        }
    }
    
    /** Records filter by matching key to regex
     */
    public static class RegexFilter extends FilterBase {
        private Pattern p;
        /** Define the filtering regex and stores it in conf
         * @param conf where the regex is set
         * @param regex regex used as a filter
         */
        public static void setPattern(Configuration conf, String regex )
            throws PatternSyntaxException {
            try {
                Pattern.compile(regex);
            } catch (PatternSyntaxException e) {
                throw new IllegalArgumentException("Invalid pattern: "+regex);
            }
            conf.set(FILTER_REGEX, regex);
        }
        
        public RegexFilter() { }
        
        /** configure the Filter by checking the configuration
         */
        public void setConf(Configuration conf) {
            String regex = conf.get(FILTER_REGEX);
            if(regex==null)
                throw new RuntimeException(FILTER_REGEX + "not set");
            this.p = Pattern.compile(regex);
            this.conf = conf;
        }


        /** Filtering method
         * If key matches the regex, return true; otherwise return false
         * @see org.apache.hadoop.mapred.SequenceFileInputFilter.Filter#accept(org.apache.hadoop.io.Writable)
         */
        public boolean accept(Writable key) {
            return p.matcher(key.toString()).matches();
        }
    }

    /** This class returns a percentage of records
     * The percentage is determined by a filtering frequency <i>f</i> using
     * the criteria record# % f == 0.
     * For example, if the frequency is 10, one out of 10 records is returned.
     */
    public static class PercentFilter extends FilterBase {
        private int frequency;
        private int count;

        /** set the frequency and stores it in conf
         * @param conf configuration
         * @param frequency filtering frequencey
         */
        public static void setFrequency(Configuration conf, int frequency ){
            if(frequency<=0)
                throw new IllegalArgumentException(
                   "Negative " + FILTER_FREQUENCY + ": "+frequency);
            conf.setInt(FILTER_FREQUENCY, frequency);
        }
        
        public PercentFilter() { }
        
        /** configure the filter by checking the configuration
         * 
         * @param conf configuration
         */
        public void setConf(Configuration conf) {
            this.frequency = conf.getInt("sequencefile.filter.frequency", 10);
            if(this.frequency <=0 ) {
                throw new RuntimeException(
                        "Negative "+FILTER_FREQUENCY+": "+this.frequency);
            }
            this.conf = conf;
        }

        /** Filtering method
         * If record# % frequency==0, return true; otherwise return false
         * @see org.apache.hadoop.mapred.SequenceFileInputFilter.Filter#accept(org.apache.hadoop.io.Writable)
         */
        public boolean accept(Writable key) {
            boolean accepted = false;
            if(count == 0)
                accepted = true;
            if( ++count == frequency ) {
                count = 0;
            }
            return accepted;
        }
    }

    /** This class returns a set of records by examing the MD5 digest of its
     * key against a filtering frequency <i>f</i>. The filtering criteria is
     * MD5(key) % f == 0.
     */
    public static class MD5Filter extends FilterBase {
        private int frequency;
        private static final MessageDigest DIGESTER;
        public static final int MD5_LEN = 16;
        private byte [] digest = new byte[MD5_LEN];
        
        static {
          try {
            DIGESTER = MessageDigest.getInstance("MD5");
          } catch (NoSuchAlgorithmException e) {
            throw new RuntimeException(e);
          }
        }


        /** set the filtering frequency in configuration
         * 
         * @param conf configuration
         * @param frequency filtering frequency
         */
        public static void setFrequency(Configuration conf, int frequency ){
            if(frequency<=0)
                throw new IllegalArgumentException(
                   "Negative " + FILTER_FREQUENCY + ": "+frequency);
            conf.setInt(FILTER_FREQUENCY, frequency);
        }
        
        public MD5Filter() { }
        
        /** configure the filter according to configuration
         * 
         * @param conf configuration
         */
        public void setConf(Configuration conf) {
            this.frequency = conf.getInt(FILTER_FREQUENCY, 10);
            if(this.frequency <=0 ) {
                throw new RuntimeException(
                        "Negative "+FILTER_FREQUENCY+": "+this.frequency);
            }
            this.conf = conf;
        }

        /** Filtering method
         * If MD5(key) % frequency==0, return true; otherwise return false
         * @see org.apache.hadoop.mapred.SequenceFileInputFilter.Filter#accept(org.apache.hadoop.io.Writable)
         */
        public boolean accept(Writable key) {
            try {
                long hashcode;
                if( key instanceof Text) {
                    hashcode = MD5Hashcode((Text)key);
                } else if( key instanceof BytesWritable) {
                    hashcode = MD5Hashcode((BytesWritable)key);
                } else {
                    ByteBuffer bb;
                    bb = Text.encode(key.toString());
                    hashcode = MD5Hashcode(bb.array(),0, bb.limit());
                }
                if(hashcode/frequency*frequency==hashcode)
                    return true;
            } catch(Exception e) {
                LOG.warn(e);
                throw new RuntimeException(e);
            }
            return false;
        }
        
        private long MD5Hashcode(Text key) throws DigestException {
            return MD5Hashcode(key.getBytes(), 0, key.getLength());
        }
        
        private long MD5Hashcode(BytesWritable key) throws DigestException {
            return MD5Hashcode(key.get(), 0, key.getSize());
        }
        synchronized private long MD5Hashcode(byte[] bytes, 
                int start, int length ) throws DigestException {
            DIGESTER.update(bytes, 0, length);
            DIGESTER.digest(digest, 0, MD5_LEN);
            long hashcode=0;
            for (int i = 0; i < 8; i++)
                hashcode |= ((digest[i] & 0xffL) << (8*(7-i)));
            return hashcode;
        }
    }
    
    private static class FilterRecordReader extends SequenceFileRecordReader {
        private Filter filter;
        
        public FilterRecordReader(Configuration conf, FileSplit split)
        throws IOException {
            super(conf, split);
            // instantiate filter
            filter = (Filter)ReflectionUtils.newInstance(
                    conf.getClass(FILTER_CLASS, PercentFilter.class), 
                    conf);
        }
        
        public synchronized boolean next(Writable key, Writable value)
                              throws IOException {
            while (next(key)) {
                if(filter.accept(key)) {
                    getCurrentValue(value);
                    return true;
                }
            }
            
            return false;
        }
    }
}
