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import java.io.IOException;
import java.util.StringTokenizer;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.ArrayWritable;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class WeatherMapReduce {
    public static class WeatherMapper extends Mapper<Object, Text, Text, IntWritable> {

        private final static Text key = new Text();
        private final static IntWritable value = new IntWritable();

        public void map(Object k, Text file, Context context) throws IOException, InterruptedException {
            StringTokenizer itr = new StringTokenizer(file.toString());
            while (itr.hasMoreTokens()) {
                String line = itr.nextToken();

                if (!line.startsWith("UK000056225") && !line.startsWith("UK000003377")) {
                    continue;
                }

                String[] data = line.split(",");

                String loc = data[0];
                String date = data[1];
                String type = data[2];
                int val = Integer.parseInt(data[3]);

                if (!type.equals("TMIN") && !type.equals("TMAX")) {
                    continue;
                }

                key.set(loc  + "," + date);
                value.set(val);

                context.write(key, value);
            }
        }
    }

    public static class WeatherReducer extends Reducer<Text, IntWritable, Text, IntWritable> {
        private IntWritable result = new IntWritable();

        public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
            boolean firstValueSet = false;
            int firstValue = 0;
            boolean secondValueSet = false;
            int secondValue = 0;

            for (IntWritable val : values) {
                if (firstValueSet) {
                    secondValue = val.get();
                    secondValueSet = true;
                } else {
                    firstValue = val.get();
                    firstValueSet = true;
                }
            }

            // only output this date if there is both a TMIN and a TMAX
            if (firstValueSet && secondValueSet) {
                int range = Math.abs(firstValue - secondValue);
                System.out.println("'" + firstValue + "' and '" + secondValue + "' has range " + range);
                result.set(range);
                context.write(key, result);
            }
        }
    }

    public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf, "WeatherMapReduce");
        job.setJarByClass(WeatherMapReduce.class);
        job.setMapperClass(WeatherMapper.class);
        job.setCombinerClass(WeatherReducer.class);
        job.setReducerClass(WeatherReducer.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);
        FileInputFormat.addInputPath(job, new Path(args[0]));
        FileOutputFormat.setOutputPath(job, new Path(args[1]));
        System.exit(job.waitForCompletion(true) ? 0 : 1);
    }
}