package os;

import java.io.PrintStream;
import java.util.concurrent.Semaphore;

class Database {

	Semaphore writeMut = new Semaphore(1);
	Semaphore readSem = new Semaphore(1);
	Semaphore mut = new Semaphore(1);
	
	private int readersWorking = 0;
	
	// Sva polja se inicijalizuju u konstruktoru
	public Database() {
	}

	// Pocetak operacije citanja
	public void readLock() {
		mut.acquireUninterruptibly();
			if(readersWorking==0)
			{
				writeMut.acquireUninterruptibly();
				System.out.println("lock read");
			}
			readersWorking++;
		mut.release();
	}

	// Pocetak operacije pisanja 
	public void writeLock() {
		writeMut.acquireUninterruptibly();
	}

	// Kraj operacije citanja
	public void readUnlock() {
		mut.acquireUninterruptibly();
		readersWorking--;
		if(readersWorking==0)
		{
			writeMut.release();
			System.out.println("unlock read");
		}
		mut.release();
	}

	// Kraj operacije pisanja 
	public void writeUnlock() {
		writeMut.release();
	}
}

public class ReadWriter {

	// Broj proizvodjaca i potrosaca
	public static final int READER_COUNT = 20;
	public static final int WRITER_COUNT = 2;

	// Potrebno vreme proizvodnje i potrosnje
	public static final long READER_TIME = 2000;
	public static final long WRITER_TIME = 500;

	// Glavna nit
	public static void main(String[] args) {

		// Napravi bazu podataka kojoj ce procesi pristupati
		Database database = new Database();

		// Napravi citaoce
		for (int i = 0; i < READER_COUNT; i++) {
			Reader r = new Reader(database);
			r.start();
		}

		// Napravi pisce
		for (int i = 0; i < WRITER_COUNT; i++) {
			Writer w = new Writer(database);
			w.start();
		}
	}

	// Sistem za ispisivanje poruka
	public static int readersWorking = 0;
	public static int readersWaiting = 0;
	public static int writersWorking = 0;
	public static int writersWaiting = 0;
	public static void print() {
		PrintStream out = (readersWorking * writersWorking != 0) ? System.err : System.out;
		out.println("Readers: " + readersWorking + " (" + readersWaiting + ") Writers: " + writersWorking + " (" + writersWaiting + ")");
	}
}

// Citalac
class Reader extends Thread {

	private static int count = 1;

	private Database database;

	// Zapamti bazu i postavi ime procesa
	public Reader(Database database) {
		this.database = database;
		setName("Reader " + count++);
	}

	@Override
	public void run() {
		while (!isInterrupted()) {
	
			// Cekaj
			try {
				Thread.sleep((long)(ReadWriter.READER_TIME + Math.random() * ReadWriter.READER_TIME));
			} catch (InterruptedException e) {
				// Nema veze
			}
			
			// Pristupi bazi
			synchronized (ReadWriter.class) { // Debug
				ReadWriter.readersWaiting++;
				ReadWriter.print();
			}
			database.readLock();
			synchronized (ReadWriter.class) { // Debug
				ReadWriter.readersWaiting--;
				ReadWriter.readersWorking++;
				ReadWriter.print();
			}
			
			// Citaj
			try {
				Thread.sleep((long)(ReadWriter.READER_TIME + Math.random() * ReadWriter.READER_TIME));
			} catch (InterruptedException e) {
				// Nema veze
			}

			// Oslobodi bazu
			database.readUnlock();
			synchronized (ReadWriter.class) { // Debug
				ReadWriter.readersWorking--;
				ReadWriter.print();
			}

		}
	}
}

// Pisac
class Writer extends Thread {

	private static int count = 1;

	private Database database;

	// Zapamti bazu i postavi ime procesa
	public Writer(Database database) {
		this.database = database;
		setName("Writer " + count++);
	}

	@Override
	public void run() {
		while (!isInterrupted()) {

			// Cekaj
			try {
				Thread.sleep((long)(ReadWriter.WRITER_TIME + Math.random() * ReadWriter.WRITER_TIME));
			} catch (InterruptedException e) {
				// Nema veze
			}
			
			// Pristupi bazi
			synchronized (ReadWriter.class) { // Debug
				ReadWriter.writersWaiting++;
				ReadWriter.print();
			}
			database.writeLock();
			synchronized (ReadWriter.class) { // Debug
				ReadWriter.writersWaiting--;
				ReadWriter.writersWorking++;
				ReadWriter.print();
			}
			
			// Pisi
			try {
				Thread.sleep((long)(ReadWriter.WRITER_TIME + Math.random() * ReadWriter.WRITER_TIME));
			} catch (InterruptedException e) {
				// Nema veze
			}

			// Oslobodi bazu
			database.writeUnlock();
			synchronized (ReadWriter.class) { // Debug
				ReadWriter.writersWorking--;
				ReadWriter.print();
			}

		}
	}
}