/*
 * Copyright 2004-2012 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.springframework.faces.webflow;

import java.io.IOException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import javax.faces.FacesException;
import javax.faces.view.facelets.ResourceResolver;

import org.springframework.context.ApplicationContext;
import org.springframework.core.io.Resource;
import org.springframework.util.ClassUtils;
import org.springframework.webflow.execution.RequestContext;
import org.springframework.webflow.execution.RequestContextHolder;

/**
 * Resolves Facelets templates using Spring Resource paths such as "classpath:foo.xhtml". Configure it via a context
 * parameter in web.xml:
 * 
 * <pre>
 * <context-param/> 
 * 	<param-name>facelets.RESOURCE_RESOLVER</param-name>
 * 	<param-value>org.springframework.faces.webflow.FlowResourceResolver</param-value> 
 * </context-param>
 * </pre>
 * 
 * @see Jsf2FlowResourceResolver
 */
public class FlowResourceResolver extends ResourceResolver {

	/**
	 * All known {@link ResourceResolver} implementations in the priority order
	 */
	private static final List<String> RESOLVERS_CLASSES;
	static {
		List<String> resolvers = new ArrayList<String>();
		resolvers.add("com.sun.faces.facelets.impl.DefaultResourceResolver");
		resolvers.add("org.apache.myfaces.view.facelets.impl.DefaultResourceResolver");
		RESOLVERS_CLASSES = Collections.unmodifiableList(resolvers);
	}

	private final ResourceResolver delegateResolver;

	public FlowResourceResolver() {
		this.delegateResolver = createDelegateResolver();
	}

	private ResourceResolver createDelegateResolver() {
		try {
			ClassLoader classLoader = getClass().getClassLoader();
			for (String resolverClass : RESOLVERS_CLASSES) {
				if (ClassUtils.isPresent(resolverClass, classLoader)) {
					return (ResourceResolver) ClassUtils.forName(resolverClass, classLoader).newInstance();
				}
			}
		} catch (Exception e) {
		}
		throw new IllegalStateException("Unable to find Default ResourceResolver");
	}

	public URL resolveUrl(String path) {

		if (!JsfUtils.isFlowRequest()) {
			return this.delegateResolver.resolveUrl(path);
		}

		try {
			RequestContext context = RequestContextHolder.getRequestContext();
			ApplicationContext flowContext = context.getActiveFlow().getApplicationContext();
			if (flowContext == null) {
				throw new IllegalStateException("A Flow ApplicationContext is required to resolve Flow View Resources");
			}

			ApplicationContext appContext = flowContext.getParent();
			Resource viewResource = appContext.getResource(path);
			if (viewResource.exists()) {
				return viewResource.getURL();
			} else {
				return this.delegateResolver.resolveUrl(path);
			}
		} catch (IOException ex) {
			throw new FacesException(ex);
		}
	}

}