/**
 * 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.flink.streaming.examples.java8.wordcount;

import java.util.Arrays;

import org.apache.flink.api.java.tuple.Tuple2;
import org.apache.flink.examples.java.wordcount.util.WordCountData;
import org.apache.flink.streaming.api.datastream.DataStream;
import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
import org.apache.flink.util.Collector;

/**
 * Implements the streaming "WordCount" program that computes a simple word occurrences
 * over text files. 
 * 
 * <p>
 * The input is a plain text file with lines separated by newline characters.
 * 
 * <p>
 * Usage: <code>WordCount <text path> <result path></code><br>
 * If no parameters are provided, the program is run with default data from {@link WordCountData}.
 * 
 * <p>
 * This example shows how to:
 * <ul>
 * <li>write a compact Flink Streaming program with Java 8 Lambda Expressions.
 * </ul>
 * 
 */
public class WordCount {
	
	// *************************************************************************
	//     PROGRAM
	// *************************************************************************
	
	public static void main(String[] args) throws Exception {
		
		if(!parseParameters(args)) {
			return;
		}
		
		// set up the execution environment
		final StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
		
		// get input data
		DataStream<String> text = getTextDataStream(env);
		
		DataStream<Tuple2<String, Integer>> counts = 
				// normalize and split each line
				text.map(line -> line.toLowerCase().split("\\W+"))
				// convert splitted line in pairs (2-tuples) containing: (word,1)
				.flatMap((String[] tokens, Collector<Tuple2<String, Integer>> out) -> {
					// emit the pairs with non-zero-length words
					Arrays.stream(tokens)
					.filter(t -> t.length() > 0)
					.forEach(t -> out.collect(new Tuple2<>(t, 1)));
				})
				// group by the tuple field "0" and sum up tuple field "1"
				.keyBy(0)
				.sum(1);

		// emit result
		if(fileOutput) {
			counts.writeAsCsv(outputPath);
		} else {
			counts.print();
		}
		
		// execute program
		env.execute("Streaming WordCount Example");
	}
	
	// *************************************************************************
	//     UTIL METHODS
	// *************************************************************************
	
	private static boolean fileOutput = false;
	private static String textPath;
	private static String outputPath;
	
	private static boolean parseParameters(String[] args) {
		
		if(args.length > 0) {
			// parse input arguments
			fileOutput = true;
			if(args.length == 2) {
				textPath = args[0];
				outputPath = args[1];
			} else {
				System.err.println("Usage: WordCount <text path> <result path>");
				return false;
			}
		} else {
			System.out.println("Executing WordCount example with built-in default data.");
			System.out.println("  Provide parameters to read input data from a file.");
			System.out.println("  Usage: WordCount <text path> <result path>");
		}
		return true;
	}
	
	private static DataStream<String> getTextDataStream(StreamExecutionEnvironment env) {
		if (fileOutput) {
			// read the text file from given input path
			return env.readTextFile(textPath);
		} else {
			// get default test text data
			return env.fromElements(WordCountData.WORDS);
		}
	}
}