import org.apache.commons.lang3.RandomStringUtils;

import java.util.Set;
import java.util.concurrent.ConcurrentSkipListSet;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicInteger;

public class Kernel {

    static final int TRIALS = 5000000;

    static Executor executor = Executors.newFixedThreadPool(20);
    static CountDownLatch latch = new CountDownLatch(TRIALS);
    private static Set<String> ids = new ConcurrentSkipListSet<String>();
    public static void main(String ... args) {
        final AtomicInteger counter = new AtomicInteger(0);
        for (int i = 1; i<=TRIALS; i++) {
            executor.execute(new Runnable() {
                @Override
                public void run() {
                    String id = new Generator().getId();
                    if (ids.contains(id)) {
                        counter.incrementAndGet();
                    } else {
                        ids.add(id);
                    }
                    latch.countDown();
                }
            });
        }
        try {
            latch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("Trials: " + TRIALS);
        System.out.println("Collisions: " + counter);
        System.out.println("Ids size: " + ids.size());
        System.exit(0);
    }

    static class Generator {
        public String getId() {
            return new StringBuilder()
                    .append(RandomStringUtils.randomAlphanumeric(4))
                    .append("-")
                    .append(RandomStringUtils.randomAlphanumeric(4))
                    .append("-")
                    .append(RandomStringUtils.randomAlphanumeric(4))
                    .append("-")
                    .append(RandomStringUtils.randomAlphanumeric(4)).toString();

        }
    }

}