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JSF 2.2+ utility library
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/*
 * Copyright OmniFaces
 *
 * 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
 *
 *     https://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.omnifaces.config;

import static org.omnifaces.util.Reflection.toClass;
import static org.omnifaces.util.Utils.isEmpty;
import static org.omnifaces.util.Utils.parseLocale;
import static org.omnifaces.util.Xml.createDocument;
import static org.omnifaces.util.Xml.getNodeList;
import static org.omnifaces.util.Xml.getTextContent;

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

import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;

import jakarta.faces.application.ResourceHandler;
import jakarta.servlet.ServletContext;

import org.omnifaces.util.Servlets;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;

/**
 * Enum singleton implementation of {@link FacesConfigXml}.
 *
 * @author Bauke Scholtz
 * @author Michele Mariotti
 * @since 3.1
 */
enum FacesConfigXmlSingleton implements FacesConfigXml {

	// Enum singleton -------------------------------------------------------------------------------------------------

	/**
	 * Returns the lazily loaded enum singleton instance.
	 */
	INSTANCE;

	// Private constants ----------------------------------------------------------------------------------------------

	private static final String APP_FACES_CONFIG_XML =
		"/WEB-INF/faces-config.xml";
	private static final String LIB_FACES_CONFIG_XML =
		"META-INF/faces-config.xml";
	private static final String XPATH_RESOURCE_BUNDLE =
		"application/resource-bundle";
	private static final String XPATH_DEFAULT_LOCALE =
		"application/locale-config/default-locale";
	private static final String XPATH_SUPPORTED_LOCALE =
		"application/locale-config/supported-locale";
	private static final String XPATH_RESOURCE_HANDLER =
		"application/resource-handler";
	private static final String XPATH_VAR =
		"var";
	private static final String XPATH_BASE_NAME =
		"base-name";
	private static final String ERROR_INITIALIZATION_FAIL =
		"FacesConfigXml failed to initialize. Perhaps your faces-config.xml contains a typo?";

	// Properties -----------------------------------------------------------------------------------------------------

	private Map resourceBundles;
	private List supportedLocales;
	private List> resourceHandlers;

	// Init -----------------------------------------------------------------------------------------------------------

	/**
	 * Perform automatic initialization whereby the servlet context is obtained from CDI.
	 */
	private FacesConfigXmlSingleton() {
		try {
			ServletContext servletContext = Servlets.getContext();
			Element facesConfigXml = loadFacesConfigXml(servletContext).getDocumentElement();
			XPath xpath = XPathFactory.newInstance().newXPath();
			resourceBundles = parseResourceBundles(facesConfigXml, xpath);
			supportedLocales = parseSupportedLocales(facesConfigXml, xpath);
			resourceHandlers = parseResourceHandlers(facesConfigXml, xpath);
		}
		catch (Exception e) {
			throw new IllegalStateException(ERROR_INITIALIZATION_FAIL, e);
		}
	}

	// Getters --------------------------------------------------------------------------------------------------------

	@Override
	public Map getResourceBundles() {
		return resourceBundles;
	}

	@Override
	public List getSupportedLocales() {
		return supportedLocales;
	}

	@Override
	public List> getResourceHandlers() {
		return resourceHandlers;
	}

	// Helpers --------------------------------------------------------------------------------------------------------

	/**
	 * Load, merge and return all faces-config.xml files found in the classpath
	 * into a single {@link Document}.
	 */
	private static Document loadFacesConfigXml(ServletContext context) throws IOException, SAXException {
		List facesConfigURLs = new ArrayList<>();
		facesConfigURLs.add(context.getResource(APP_FACES_CONFIG_XML));
		facesConfigURLs.addAll(Collections.list(Thread.currentThread().getContextClassLoader().getResources(LIB_FACES_CONFIG_XML)));
		return createDocument(facesConfigURLs);
	}

	/**
	 * Create and return a mapping of all resource bundle base names by var found in the given document.
	 * @throws XPathExpressionException
	 */
	private static Map parseResourceBundles(Element facesConfigXml, XPath xpath) throws XPathExpressionException {
		Map resourceBundles = new LinkedHashMap<>();
		NodeList resourceBundleNodes = getNodeList(facesConfigXml, xpath, XPATH_RESOURCE_BUNDLE);

		for (int i = 0; i < resourceBundleNodes.getLength(); i++) {
			Node node = resourceBundleNodes.item(i);

			String var = xpath.compile(XPATH_VAR).evaluate(node).trim();
			String baseName = xpath.compile(XPATH_BASE_NAME).evaluate(node).trim();
			resourceBundles.computeIfAbsent(var, k -> baseName);
		}

		return Collections.unmodifiableMap(resourceBundles);
	}

	/**
	 * Create and return a list of default locale and all supported locales in same order as in the given document.
	 * @throws XPathExpressionException
	 */
	private static List parseSupportedLocales(Element facesConfigXml, XPath xpath) throws XPathExpressionException {
		List supportedLocales = new ArrayList<>();
		String defaultLocale = xpath.compile(XPATH_DEFAULT_LOCALE).evaluate(facesConfigXml).trim();

		if (!isEmpty(defaultLocale)) {
			supportedLocales.add(parseLocale(defaultLocale));
		}

		NodeList supportedLocaleNodes = getNodeList(facesConfigXml, xpath, XPATH_SUPPORTED_LOCALE);

		for (int i = 0; i < supportedLocaleNodes.getLength(); i++) {
			Locale supportedLocale = parseLocale(getTextContent(supportedLocaleNodes.item(i)));

			if (!supportedLocales.contains(supportedLocale)) {
				supportedLocales.add(supportedLocale);
			}
		}

		return Collections.unmodifiableList(supportedLocales);
	}

	/**
	 * Create and return a list of all resource handlers in same order as in the given document.
	 * @throws XPathExpressionException
	 */
	private static List> parseResourceHandlers(Element facesConfigXml, XPath xpath) throws XPathExpressionException {
		List> resourceHandlers = new ArrayList<>();
		NodeList resourceHandlerNodes = getNodeList(facesConfigXml, xpath, XPATH_RESOURCE_HANDLER);

		for (int i = 0; i < resourceHandlerNodes.getLength(); i++) {
			Class resourceHandler = toClass(getTextContent(resourceHandlerNodes.item(i)));
			resourceHandlers.add(resourceHandler);
		}

		return Collections.unmodifiableList(resourceHandlers);
	}

}