/*
 * Copyright 2002-2007 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.beans.factory.xml;

import java.io.IOException;
import java.util.Properties;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.xml.sax.EntityResolver;
import org.xml.sax.InputSource;

import org.springframework.beans.FatalBeanException;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.Resource;
import org.springframework.core.io.support.PropertiesLoaderUtils;
import org.springframework.util.Assert;

/**
 * {@link EntityResolver} implementation that attempts to resolve schema URLs into
 * local {@link ClassPathResource classpath resources} using a set of mappings files.
 *
 * <p>By default, this class will look for mapping files in the classpath using the pattern:
 * <code>META-INF/spring.schemas</code> allowing for multiple files to exist on the
 * classpath at any one time.
 *
 * The format of <code>META-INF/spring.schemas</code> is a properties
 * file where each line should be of the form <code>systemId=schema-location</code>
 * where <code>schema-location</code> should also be a schema file in the classpath.
 * Since systemId is commonly a URL, one must be careful to escape any ':' characters
 * which are treated as delimiters in properties files.
 *
 * <p>The pattern for the mapping files can be overidden using the
 * {@link #PluggableSchemaResolver(ClassLoader, String)} constructor
 *
 * @author Rob Harrop
 * @author Juergen Hoeller
 * @since 2.0
 */
public class PluggableSchemaResolver implements EntityResolver {

	/**
	 * The location of the file that defines schema mappings.
	 * Can be present in multiple JAR files.
	 */
	public static final String DEFAULT_SCHEMA_MAPPINGS_LOCATION = "META-INF/spring.schemas";


	private static final Log logger = LogFactory.getLog(PluggableSchemaResolver.class);

	private final ClassLoader classLoader;

	private final String schemaMappingsLocation;

	/** Stores the mapping of schema URL -> local schema path */
	private Properties schemaMappings;


	/**
	 * Loads the schema URL -> schema file location mappings using the default
	 * mapping file pattern "META-INF/spring.schemas".
	 * @param classLoader the ClassLoader to use for loading
	 * (can be <code>null</code>) to use the default ClassLoader)
	 * @see PropertiesLoaderUtils#loadAllProperties(String, ClassLoader)
	 */
	public PluggableSchemaResolver(ClassLoader classLoader) {
		this.classLoader = classLoader;
		this.schemaMappingsLocation = DEFAULT_SCHEMA_MAPPINGS_LOCATION;
	}

	/**
	 * Loads the schema URL -> schema file location mappings using the given
	 * mapping file pattern.
	 * @param classLoader the ClassLoader to use for loading
	 * (can be <code>null</code>) to use the default ClassLoader)
	 * @param schemaMappingsLocation the location of the file that defines schema mappings
	 * (must not be empty)
	 * @see PropertiesLoaderUtils#loadAllProperties(String, ClassLoader)
	 */
	public PluggableSchemaResolver(ClassLoader classLoader, String schemaMappingsLocation) {
		Assert.hasText(schemaMappingsLocation, "'schemaMappingsLocation' must not be empty");
		this.classLoader = classLoader;
		this.schemaMappingsLocation = schemaMappingsLocation;
	}


	public InputSource resolveEntity(String publicId, String systemId) throws IOException {
		if (logger.isTraceEnabled()) {
			logger.trace("Trying to resolve XML entity with public id [" + publicId +
					"] and system id [" + systemId + "]");
		}
		if (systemId != null) {
			String resourceLocation = getSchemaMapping(systemId);
			if (resourceLocation != null) {
				Resource resource = new ClassPathResource(resourceLocation, this.classLoader);
				InputSource source = new InputSource(resource.getInputStream());
				source.setPublicId(publicId);
				source.setSystemId(systemId);
				if (logger.isDebugEnabled()) {
					logger.debug("Found XML schema [" + systemId + "] in classpath: " + resourceLocation);
				}
				return source;
			}
		}
		return null;
	}

	protected String getSchemaMapping(String systemId) {
		if (this.schemaMappings == null) {
			if (logger.isDebugEnabled()) {
				logger.debug("Loading schema mappings from [" + this.schemaMappingsLocation + "]");
			}
			try {
				this.schemaMappings =
						PropertiesLoaderUtils.loadAllProperties(this.schemaMappingsLocation, this.classLoader);
				if (logger.isDebugEnabled()) {
					logger.debug("Loaded schema mappings: " + this.schemaMappings);
				}
			}
			catch (IOException ex) {
				throw new FatalBeanException(
						"Unable to load schema mappings from location [" + this.schemaMappingsLocation + "]", ex);
			}
		}
		return this.schemaMappings.getProperty(systemId);
	}

}