package com.semanticsquare.concurrency;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

public class MeetUpEventSimulator {
	
	public static class MeetUpEvent {
		private String name;
		private AtomicInteger count = new AtomicInteger(1); // 1 for organizer
		
		public MeetUpEvent(String name) {
			this.name = name;			
		}
		
		public void attending(int guestCount) {
			if (guestCount == 1) {
				count.incrementAndGet();
			} else {
				count.addAndGet(guestCount); 
			}
		}
		
		public void notAttending(int guestCount) {			
			if (guestCount == 1) {
				count.decrementAndGet();
			} else {
				
				boolean updated = false;
				
				while(!updated){
		        	int currentCount = count.get();
					int newCount = currentCount - guestCount;
		            updated = count.compareAndSet(currentCount, newCount);
		        }	
			}
		}
		
		public int getCount() {
			return count.get();
		}
	}
	
	public static void main(String[] args) {
		MeetUpEvent jugBoston = new MeetUpEvent("The Boston Java User Group");
		
		Thread user1 = new Thread(new Runnable() {
			@Override
			public void run() {
				jugBoston.attending(4);
				System.out.println(Thread.currentThread().getName() + " : " + jugBoston.getCount());
			}			
		});
		
		Thread user2 = new Thread(new Runnable() {
			@Override
			public void run() {
				jugBoston.attending(3);
				System.out.println(Thread.currentThread().getName() + " : " + jugBoston.getCount());
				jugBoston.notAttending(3);
				System.out.println(Thread.currentThread().getName() + " : " + jugBoston.getCount());
			}			
		});
		Thread user3 = new Thread(new Runnable() {
			@Override
			public void run() {
				jugBoston.attending(1);
				System.out.println(Thread.currentThread().getName() + " : " + jugBoston.getCount());
			}			
		});
		
		user1.setName("User 1");
		user2.setName("User 2");
		user3.setName("User 3");
		
		user1.start();
		sleep(1);
		user2.start();
		sleep(2);
		user3.start();
		sleep(2);
		System.out.println("Total attending : " + jugBoston.getCount());
	}

	private static void sleep(int i) {
		try {
			TimeUnit.SECONDS.sleep(i);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
}