/*
 * Copyright 2002-2015 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.http.converter.xml;

import java.io.IOException;
import java.io.StringReader;
import javax.xml.bind.JAXBElement;
import javax.xml.bind.JAXBException;
import javax.xml.bind.MarshalException;
import javax.xml.bind.Marshaller;
import javax.xml.bind.PropertyException;
import javax.xml.bind.UnmarshalException;
import javax.xml.bind.Unmarshaller;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlType;
import javax.xml.transform.Result;
import javax.xml.transform.Source;
import javax.xml.transform.sax.SAXSource;
import javax.xml.transform.stream.StreamSource;

import org.xml.sax.EntityResolver;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;
import org.xml.sax.helpers.XMLReaderFactory;

import org.springframework.core.annotation.AnnotationUtils;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.http.converter.HttpMessageConversionException;
import org.springframework.http.converter.HttpMessageNotReadableException;
import org.springframework.http.converter.HttpMessageNotWritableException;
import org.springframework.util.ClassUtils;

/**
 * Implementation of {@link org.springframework.http.converter.HttpMessageConverter
 * HttpMessageConverter} that can read and write XML using JAXB2.
 *
 * <p>This converter can read classes annotated with {@link XmlRootElement} and
 * {@link XmlType}, and write classes annotated with {@link XmlRootElement},
 * or subclasses thereof.
 *
 * <p>Note that if using Spring's Marshaller/Unmarshaller abstractions from the
 * {@code spring-oxm} module you should can the
 * {@link MarshallingHttpMessageConverter} instead.
 *
 * @author Arjen Poutsma
 * @author Sebastien Deleuze
 * @author Rossen Stoyanchev
 * @since 3.0
 * @see MarshallingHttpMessageConverter
 */
public class Jaxb2RootElementHttpMessageConverter extends AbstractJaxb2HttpMessageConverter<Object> {

	private boolean supportDtd = false;

	private boolean processExternalEntities = false;


	/**
	 * Indicates whether DTD parsing should be supported.
	 * <p>Default is {@code false} meaning that DTD is disabled.
	 */
	public void setSupportDtd(boolean supportDtd) {
		this.supportDtd = supportDtd;
	}

	/**
	 * Whether DTD parsing is supported.
	 */
	public boolean isSupportDtd() {
		return this.supportDtd;
	}

	/**
	 * Indicates whether external XML entities are processed when converting to a Source.
	 * <p>Default is {@code false}, meaning that external entities are not resolved.
	 * <p><strong>Note:</strong> setting this option to {@code true} also
	 * automatically sets {@link #setSupportDtd} to {@code true}.
	 */
	public void setProcessExternalEntities(boolean processExternalEntities) {
		this.processExternalEntities = processExternalEntities;
		if (processExternalEntities) {
			setSupportDtd(true);
		}
	}

	/**
	 * Returns the configured value for whether XML external entities are allowed.
	 */
	public boolean isProcessExternalEntities() {
		return this.processExternalEntities;
	}


	@Override
	public boolean canRead(Class<?> clazz, MediaType mediaType) {
		return (clazz.isAnnotationPresent(XmlRootElement.class) || clazz.isAnnotationPresent(XmlType.class)) &&
				canRead(mediaType);
	}

	@Override
	public boolean canWrite(Class<?> clazz, MediaType mediaType) {
		return (AnnotationUtils.findAnnotation(clazz, XmlRootElement.class) != null && canWrite(mediaType));
	}

	@Override
	protected boolean supports(Class<?> clazz) {
		// should not be called, since we override canRead/Write
		throw new UnsupportedOperationException();
	}

	@Override
	protected Object readFromSource(Class<?> clazz, HttpHeaders headers, Source source) throws IOException {
		try {
			source = processSource(source);
			Unmarshaller unmarshaller = createUnmarshaller(clazz);
			if (clazz.isAnnotationPresent(XmlRootElement.class)) {
				return unmarshaller.unmarshal(source);
			}
			else {
				JAXBElement<?> jaxbElement = unmarshaller.unmarshal(source, clazz);
				return jaxbElement.getValue();
			}
		}
		catch (NullPointerException ex) {
			if (!isSupportDtd()) {
				throw new HttpMessageNotReadableException("NPE while unmarshalling. " +
						"This can happen on JDK 1.6 due to the presence of DTD " +
						"declarations, which are disabled.", ex);
			}
			throw ex;
		}
		catch (UnmarshalException ex) {
			throw new HttpMessageNotReadableException("Could not unmarshal to [" + clazz + "]: " + ex.getMessage(), ex);

		}
		catch (JAXBException ex) {
			throw new HttpMessageConversionException("Could not instantiate JAXBContext: " + ex.getMessage(), ex);
		}
	}

	protected Source processSource(Source source) {
		if (source instanceof StreamSource) {
			StreamSource streamSource = (StreamSource) source;
			InputSource inputSource = new InputSource(streamSource.getInputStream());
			try {
				XMLReader xmlReader = XMLReaderFactory.createXMLReader();
				xmlReader.setFeature("http://apache.org/xml/features/disallow-doctype-decl", !isSupportDtd());
				String featureName = "http://xml.org/sax/features/external-general-entities";
				xmlReader.setFeature(featureName, isProcessExternalEntities());
				if (!isProcessExternalEntities()) {
					xmlReader.setEntityResolver(NO_OP_ENTITY_RESOLVER);
				}
				return new SAXSource(xmlReader, inputSource);
			}
			catch (SAXException ex) {
				logger.warn("Processing of external entities could not be disabled", ex);
				return source;
			}
		}
		else {
			return source;
		}
	}

	@Override
	protected void writeToResult(Object o, HttpHeaders headers, Result result) throws IOException {
		try {
			Class<?> clazz = ClassUtils.getUserClass(o);
			Marshaller marshaller = createMarshaller(clazz);
			setCharset(headers.getContentType(), marshaller);
			marshaller.marshal(o, result);
		}
		catch (MarshalException ex) {
			throw new HttpMessageNotWritableException("Could not marshal [" + o + "]: " + ex.getMessage(), ex);
		}
		catch (JAXBException ex) {
			throw new HttpMessageConversionException("Could not instantiate JAXBContext: " + ex.getMessage(), ex);
		}
	}

	private void setCharset(MediaType contentType, Marshaller marshaller) throws PropertyException {
		if (contentType != null && contentType.getCharset() != null) {
			marshaller.setProperty(Marshaller.JAXB_ENCODING, contentType.getCharset().name());
		}
	}


	private static final EntityResolver NO_OP_ENTITY_RESOLVER = new EntityResolver() {
		@Override
		public InputSource resolveEntity(String publicId, String systemId) {
			return new InputSource(new StringReader(""));
		}
	};

}
