/*
 * Copyright 2005-2010 the original author or authors.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.wamblee.test.transactions;

import java.util.ArrayList;
import java.util.List;

import javax.transaction.UserTransaction;

import org.wamblee.general.ThreadSpecificProxyFactory;
import org.wamblee.test.persistence.JpaBuilder;

/**
 * 
 * <p>
 * Simple transaction manager provides a simple mechanism to manage transactions
 * in test code through the {@link UserTransaction} object.
 * To construct the transaction manager use: 
 * </p>
 * <pre>
 *      SimpleTransactionManager manager = 
 *          new SimpleTransactionManager(new DefaultUserTransactionFactory());
 * </pre>
 * 
 * <p>
 * Next, add resources to manage using {@link #addResource(TransactionResource)}:
 * <pre>
 *      manager.addResource(jpaTester.getJpaBuilder());
 * </pre>
 * <p>
 * As you can see from the above, {@link JpaBuilder} is a resource that can be used
 * so this mechanism can be used with JPA testing. 
 * </p>
 * 
 * <p>
 * The next step is to manage transactions using the standard <code>UserTransaction</code>
 * APIs:
 * </p>
 * <pre>
 *      UserTransaction transaction = manager.getTransaction();
 *      transaction.begin();
 *     
 *      ... do work...
 *  
 *      transaction.commit(); 
 * </pre>
 * 
 * @author Erik Brakkee
 * 
 */
public class SimpleTransactionManager {

    private UserTransactionFactory factory;
    private ThreadLocal<UserTransaction> transaction; 
    private UserTransactionCallback callback;
    private List<TransactionResource> resources;

    /**
     * Constructs the transaction manager.
     * 
     * @param aFactory
     *            Factory to create transactions with.
     */
    public SimpleTransactionManager(UserTransactionFactory aFactory) {
        factory = aFactory;
        transaction = new ThreadLocal<UserTransaction>();
        callback = new UserTransactionCallback() {

            @Override
            public void transactionFinished() {
                transaction.set(null);
            }
        };
        resources = new ArrayList<TransactionResource>();
    }

    /**
     * Adds a resource to manage. Adding resources is no longer allowed after
     * the first transaction has started.
     * 
     * @param aResource
     *            Resource.
     */
    public void addResource(TransactionResource aResource) {
        resources.add(aResource);
    }

    /**
     * Gets the user transaction. This is a contextual reference, meaning that
     * it will delegate to the appropriate thread-specific user transaction. 
     * It is also safe to store in a JNDI tree and for caching by applications. 
     * 
     * @return User transaction.
     */
    public UserTransaction getTransaction() {
        return new AutoCreateUserTransaction(this);
    }
    
    UserTransaction getOrCreateThreadSpecificTransaction() { 
        UserTransaction tx = transaction.get();
        if (tx == null) {
            tx = factory.create(callback, resources);
            transaction.set(tx);
        }
        return tx;
    }
    
    /**
     * Gets the thread-specific transaction object. 
     * @return Transaction object. 
     */
    UserTransaction getThreadSpecificTransaction() { 
       getTransaction(); // create tx if needed
       return transaction.get();
    }
}