import java.util.List;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;


public class SimpleExecutorCompletionServiceTester extends Concurrent<Integer> {
	
	private static final int N_TASKS_PER_TESTER = 10;
	private static final ExecutorService ecs = Executors.newCachedThreadPool();
	private static final SimpleExecutorCompletionService<Integer> secs = 
							new SimpleExecutorCompletionService<>(ecs);

	public SimpleExecutorCompletionServiceTester(Integer[] args) {
		super(args);
	}

	private static int sleepAndReturnTime(int sleepTimeMs) throws InterruptedException {
		Thread.sleep(sleepTimeMs);
		return sleepTimeMs;
	}

	public static void main(String[] args) {
		new SimpleExecutorCompletionServiceTester(new Integer[]{1, 2, 3, 4, 5}).run();
		List<Runnable> unstartedTasks = ecs.shutdownNow();
		if (!unstartedTasks.isEmpty())
			System.out.println("Still some unstarted tasks left after end of all tester threads!?");
		try {
			ecs.awaitTermination(1, TimeUnit.SECONDS);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}

	@Override
	protected void perform(Integer testerNr) {
		
		for (int i = 0; i < N_TASKS_PER_TESTER; ++i) {
			secs.submit(() -> sleepAndReturnTime(10+10*(int)(Math.random()*10)));
			// Note that submit's result is ignored here
		}
		
		for (int i = 0; i < N_TASKS_PER_TESTER; ++i) {
			Future<Integer> fut = null;
		    do {
				fut = secs.poll();
				if (fut == null)
					try {
						// No finished task right now => wait a bit (but less than the minimal task duration!)
						// before polling again
						Thread.sleep((long) (Math.random()*5));
					} catch (InterruptedException e) {
						// Nothing to do here: Sleep time is still random even if interrupted
					}
		    } while (fut == null);
			try {
				System.out.println("Tester " + testerNr + " received result " + fut.get());
			} catch (InterruptedException | ExecutionException e) {
				e.printStackTrace();
				return;
			}
		}
		System.out.println("Tester " + testerNr + " ends.");
	}

}