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package blah.concurrency.second;

import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.LockSupport;

import lombok.val;

public class JobQueue {

	final Locker emptySlotsLocker = new Locker();
	final Locker fullSlotsLocker = new Locker();

	final AtomicReference[] jobs;
	final Cursor readCursor;
	final Cursor writeCursor;
	final int bufferSize;

	volatile int wroteData = 0;

	@SuppressWarnings("unchecked")
	public JobQueue( final int bufferSize ) {
		this.jobs = new AtomicReference[ bufferSize ];
		this.readCursor = new Cursor(bufferSize);
		this.writeCursor = new Cursor(bufferSize);
		this.bufferSize = bufferSize;
		preAllocateBuffer();
	}

	void preAllocateBuffer() {
		for ( int i=0; i();
	}

	public void put( final Job job ) throws InterruptedException {
		val writablePosition = writeCursor.next();
		final AtomicReference reference = this.jobs[ writablePosition ];
		while( !reference.compareAndSet(null, job))
			LockSupport.parkNanos(reference, 1l);
		wroteData++;
	}

	int waitUntilHaveWritableSlots() {
		return writeCursor.next();
	}

	boolean haveWritableSlots() {
		return this.wroteData <= bufferSize;
	}

	public Job get() throws InterruptedException {
		val readableSlot = waitUntilHaveReadableSlots();
		final Job job = readableSlot.getAndSet(null);
		this.wroteData--;
		return job;
	}

	AtomicReference waitUntilHaveReadableSlots() {
		final AtomicReference reference = this.jobs[ readCursor.next() ];
		while( reference.get() == null )
			LockSupport.parkNanos(reference, 1l);
		return reference;
	}

	boolean haveReadbleData() {
		return this.wroteData > 0;
	}
}