// Imports
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.IntWritable;
import org.apache.hadoop.io.Text;
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;

// Set up class WordCount
public class WordCount {

	// Mapper Class
	public static class TokenizerMapper extends Mapper<Object, Text, Text, IntWritable>{

		// Set up IntWritable
		private final static IntWritable one = new IntWritable(1);

		// Variable for word.
		private Text word = new Text();

		// Map function
		public void map(Object key, Text value, Context context) throws IOException, InterruptedException {

			// Convert value to string.
			StringTokenizer itr = new StringTokenizer(value.toString());

			// Iterate through StringTokenizer.
			while (itr.hasMoreTokens()) {
				word.set(itr.nextToken());
				context.write(word, one);
			}
		}
	}

	// Reducer Class
	public static class IntSumReducer extends Reducer<Text,IntWritable,Text,IntWritable> {

		// Set up IntWritable
		private IntWritable result = new IntWritable();
		String[] search = new String[] {"education", "politics", "sports", "agriculture"};

		// Reduce function.
		public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {

			String tmp = key.toString().toLowerCase();

			for(int i = 0; i < search.length; i++) {
				if (tmp.contains(search[i])) {

					// Sum all occurences of a word.
					int sum = 0;
					for (IntWritable val : values) {
						sum += val.get();
					}

					// Set result, context.
					result.set(sum);
					context.write(new Text(search[i]), result);
				}
			}
		}
	}

	// Main function.
	public static void main(String[] args) throws Exception {

		// Create new config object.
		Configuration conf = new Configuration();

		// Set up a new job and give it a name.
		Job job = Job.getInstance(conf, "word count");

		// When creating jar, use this class name.
		job.setJarByClass(WordCount.class);

		// Class for mapping.
		job.setMapperClass(TokenizerMapper.class);

		// Class for combining.
		job.setCombinerClass(IntSumReducer.class);

		// Class for reducing.
		job.setReducerClass(IntSumReducer.class);

		// What object type is the output key.
		job.setOutputKeyClass(Text.class);

		// What object type is the output value.
		job.setOutputValueClass(IntWritable.class);

		// Set input and output paths.
		FileInputFormat.addInputPath(job, new Path(args[0]));
		FileOutputFormat.setOutputPath(job, new Path(args[1]));

		// Exit when done.
		System.exit(job.waitForCompletion(true) ? 0 : 1);

	}
}