import java.time.Instant;
import java.util.concurrent.*;

public class RateLimiting {
    public static void main(String[] args) throws InterruptedException {
        // First we'll look at basic rate limiting. Suppose
        // we want to limit our handling of incoming requests.
        // We'll serve these requests off a BlockingQueue of the
        // same name.
        BlockingQueue<Integer> requests = new ArrayBlockingQueue<>(5);
        for (int i = 1; i <= 5; i++) {
            requests.offer(i);
        }

        // This ScheduledExecutorService will execute a task
        // every 200 milliseconds. This is the regulator in
        // our rate limiting scheme.
        ScheduledExecutorService limiter = Executors.newScheduledThreadPool(1);

        // By waiting for the next execution before serving each request,
        // we limit ourselves to 1 request every 200 milliseconds.
        limiter.scheduleAtFixedRate(() -> {
            try {
                Integer req = requests.take();
                System.out.println("request " + req + " " + Instant.now());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }, 0, 200, TimeUnit.MILLISECONDS);

        // We may want to allow short bursts of requests in
        // our rate limiting scheme while preserving the
        // overall rate limit. We can accomplish this by
        // using a semaphore. This burstyLimiter
        // will allow bursts of up to 3 events.
        Semaphore burstyLimiter = new Semaphore(3);

        // Every 200 milliseconds we'll try to add a new
        // permit to burstyLimiter, up to its limit of 3.
        ScheduledExecutorService burstyLimiterRefill = Executors.newScheduledThreadPool(1);
        burstyLimiterRefill.scheduleAtFixedRate(burstyLimiter::release, 200, 200, TimeUnit.MILLISECONDS);

        // Now simulate 5 more incoming requests. The first
        // 3 of these will benefit from the burst capability
        // of burstyLimiter.
        BlockingQueue<Integer> burstyRequests = new ArrayBlockingQueue<>(5);
        for (int i = 1; i <= 5; i++) {
            burstyRequests.offer(i);
        }

        ExecutorService burstyWorker = Executors.newSingleThreadExecutor();
        burstyWorker.execute(() -> {
            while (true) {
                try {
                    burstyLimiter.acquire();
                    Integer req = burstyRequests.take();
                    System.out.println("request " + req + " " + Instant.now());
                } catch (InterruptedException e) {
                    break;
                }
            }
        });

        // Let the program run for a while
        Thread.sleep(2000);

        // Shutdown executors
        limiter.shutdown();
        burstyLimiterRefill.shutdown();
        burstyWorker.shutdown();
    }
}