import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.concurrent.locks.Condition;

public class SodaMachine {
    private final Lock lock = new ReentrantLock();
    private final Condition hasSodaToBuy = lock.newCondition();
    private final Condition needsRefill = lock.newCondition();
    private final int capacity;
    private int sodaCount = 0;

    public SodaMachine(int capacity) {
        this.capacity = capacity;
    }

    public void buySoda() {
        lock.lock();
        try {
            while (sodaCount == 0) {
                hasSodaToBuy.await();
            }

            sodaCount--;
            System.out.println("Buying a soda, remaining count is " + sodaCount);

            if (sodaCount == 0) {
                needsRefill.signalAll();
            }
        } catch (InterruptedException e) {
            System.out.println("Got interrupted while trying to buy soda.");
        } finally {
            lock.unlock();
        }
    }

    public void refill() {
        lock.lock();
        try {
            while (sodaCount > 0) {
                needsRefill.await();
            }

            sodaCount = capacity;
            System.out.println("Refilling, soda count is " + sodaCount);

            hasSodaToBuy.signalAll();
        } catch (InterruptedException e) {
            System.out.println("Got interrupted while trying to refill.");
        } finally {
            lock.unlock();
        }
    }
}