package net.oxbeef.transaction;

import java.util.Collection;
import java.util.Iterator;

import javax.ejb.Remote;
import javax.ejb.Stateless;
import javax.ejb.TransactionAttribute;
import javax.ejb.TransactionAttributeType;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

@Stateless
@Remote(DriverRemote.class)
public class Driver implements DriverRemote {

	@PersistenceContext
	protected EntityManager em;

// MAIN ENTRY POINT
	@TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
	public void growLegs() throws Exception {
		Collection c = em.createQuery("from Tiger t order by t.numLegs desc")
				.getResultList();
		Tiger t;
		int size = c.size();
		for (Iterator i = c.iterator(); i.hasNext();) {
			t = (Tiger) i.next();
			t.setNumLegs(t.getNumLegs() + 1);

			// 50% chance of fail overall
			double prob = Math.pow(0.5, 1. / size);
			if (Math.random() > prob) {
				// Emulated failure causes rollback
//				throw new RollingException();
				try {
					forbidden(t);
				} catch( Exception e ) {
					throw new RollingException();
				}
			}
			// Synchronize the persistence context to the DB
			// All flushed updates will be removed from the DB
			// if the transaction is rolled back
			em.flush();
		}

	}

// execution has 50% chance of reaching here. It does get here, but doesn't fail.
	@TransactionAttribute(TransactionAttributeType.NEVER)
	protected void forbidden(Tiger t) {
		System.out.println("trying to do something here");
		t.setNumLegs(0);
		em.flush();
		// why didn't it fail with an EJBException??
	}
	

// just return a list of what's in the db
	public int[] getValues() {
		int[] list;
		try {
			Collection c = em.createQuery(
					"from Tiger t order by t.numLegs desc").getResultList();
			list = new int[c.size()];
			int count = 0;
			for (Iterator i = c.iterator(); i.hasNext();) {
				list[count++] = ((Tiger) i.next()).getNumLegs();
			}
		} catch (Exception e) {
			e.printStackTrace();
			return null;
		}
		return list;
	}
}