import java.util.concurrent.Semaphore;

public class BlockingQueue<T> extends Thread{

    T[] contents;
    int capacity;
    int front;
    int back;

    public BlockingQueue(int capacity) {
        contents = (T[]) new Object[capacity];
        this.capacity = capacity;
        front = back = 0;
    }

    public void enqueue(T item) throws InterruptedException {
//        if (this.back == this.capacity){
//            System.out.println("The Queue is full. Item will not be added.\n"); //polna redica
//        } else{
//            contents[back] = item; // dodava item i go zgolemuva back za 1;
//            back++;
//        }
        dequeueSemamphore.release(1);
        contents[back] = item;
        back++;
    }
    public T dequeue() throws InterruptedException {
//        if (this.back == 0){
//            System.out.println("Queue is empty\n");
//            return null;
//        }else{
//            T item = contents[0];
//            for (int i = 0; i < this.back-1; i++) {
//                contents[i] = contents[i+1];
//            }
//            contents[back] = null; // brisam element sto e ostanat na krajot;
//            this.back--;
//            return item;
//        }
        dequeueSemamphore.acquire();
        T item = contents[0];
        for (int i = 0; i < this.back-1; i++) {
            contents[i] = contents[i+1];
        }
        contents[back] = null;
        back--;
        return item;

    }
    public void print(){
        if (front==back){
            System.out.println("Queue is empty...");
            return;
        }
        for (int i = front; i < back; i++) {
            System.out.print(contents[i] + " ");
        }
        System.out.println();
    }

    public static Semaphore dequeueSemamphore = new Semaphore(0);
    public static void main(String[] args) throws InterruptedException {
        BlockingQueue<Integer> blockingQueue = new BlockingQueue<>(100);
        //treba da se testira
        blockingQueue.enqueue(2);
        blockingQueue.enqueue(3);
        blockingQueue.enqueue(5);
        blockingQueue.enqueue(1);
        blockingQueue.enqueue(7);
        blockingQueue.enqueue(0);

        blockingQueue.print();
        System.out.println("Brisam");
        blockingQueue.dequeue();
        blockingQueue.dequeue();
        blockingQueue.dequeue();
        blockingQueue.dequeue();
        blockingQueue.dequeue();
        blockingQueue.dequeue(); //posleden legalen dequeue
        blockingQueue.dequeue(); //ilegalen dequeue. tuka nema da ima dozvoli pa programata se stava vo blocking mode
        blockingQueue.enqueue(5); //dodavam vo prazen queue
        blockingQueue.print(); // print metoda
    }
}