/*
 * 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.inject;

import java.util.NoSuchElementException;
import java.util.ServiceLoader;

/**
 * Utility for obtaining an implementation of the {@link InjectorFactory} using
 * {@link ServiceLoader} and for obtaining a {@link SimpleInjector}. 
 * 
 * The builder takes care that the factory and simple injector are built only once. 
 * For test code, make sure to call {@link #setInjectorFactory(InjectorFactory)}
 * before each test case to force the retrieval of a new factory and injector. This 
 * is important because if the simple injector is not created again it will use 
 * cached {@link Injector} instances from other tests. 
 * 
 * @author Erik Brakkee
 */
public class InjectorBuilder {

    private static InjectorFactory FACTORY;
    
    private static SimpleInjector INJECTOR; 

    /**
     * Sets the injector factory. This is useful for testing. 
     * @param aFactory Factory to use. 
     */
    public static void setInjectorFactory(InjectorFactory aFactory) {
        FACTORY = aFactory;
        INJECTOR = new SimpleInjector(aFactory);
    }

    /**
     * Gets the injector factory by using the first one found using
     * {@link ServiceLoader}.
     * 
     * @return InjectorFactory.
     */
    public static InjectorFactory getInjectorFactory() {
        if (FACTORY == null) {
            FACTORY = findInjectorFactory(); 
            INJECTOR = new SimpleInjector(FACTORY);
        }
        return FACTORY;
    }
    
    /**
     * Gets an injector that support injection into any type of object and 
     * performs caching of the injector obtained from the {@link InjectorFactory}.
     * @return Injector.
     */
    public static Injector getInjector() { 
        getInjectorFactory();
        return INJECTOR;
    }

    /**
     * Finds the injector factory musing <code>ServiceLoader</code>
     * 
     * @return InjectorFactory.
     */
    private static InjectorFactory findInjectorFactory() {
        ServiceLoader<InjectorFactory> factories = ServiceLoader
            .load(InjectorFactory.class);
        try {
            return (InjectorFactory) factories.iterator().next();
        } catch (NoSuchElementException e) {
            throw new RuntimeException("Can not find InjectorFactory to use");
        }
    }
}