/*
 * Copyright 2002-2018 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.codec.xml;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.function.Function;
import javax.xml.XMLConstants;
import javax.xml.bind.JAXBElement;
import javax.xml.bind.JAXBException;
import javax.xml.bind.UnmarshalException;
import javax.xml.bind.Unmarshaller;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlSchema;
import javax.xml.bind.annotation.XmlType;
import javax.xml.namespace.QName;
import javax.xml.stream.XMLEventReader;
import javax.xml.stream.events.XMLEvent;

import org.reactivestreams.Publisher;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import org.springframework.core.ResolvableType;
import org.springframework.core.codec.AbstractDecoder;
import org.springframework.core.codec.CodecException;
import org.springframework.core.codec.DecodingException;
import org.springframework.core.codec.Hints;
import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.core.log.LogFormatUtils;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.MimeType;
import org.springframework.util.MimeTypeUtils;
import org.springframework.util.xml.StaxUtils;

Decode from a bytes stream containing XML elements to a stream of Objects (POJOs). 
Author:
Sebastien Deleuze, Arjen Poutsma
See Also:
Jaxb2XmlEncoder
Since:
5.0/**
 * Decode from a bytes stream containing XML elements to a stream of
 * {@code Object}s (POJOs).
 *
 * @author Sebastien Deleuze
 * @author Arjen Poutsma
 * @since 5.0
 * @see Jaxb2XmlEncoder
 */
public class Jaxb2XmlDecoder extends AbstractDecoder<Object> {

	
The default value for JAXB annotations.
See Also:
name.name()
XmlRootElement.namespace()
XmlType.name()
XmlType.namespace()/**
	 * The default value for JAXB annotations.
	 * @see XmlRootElement#name()
	 * @see XmlRootElement#namespace()
	 * @see XmlType#name()
	 * @see XmlType#namespace()
	 */
	private static final String JAXB_DEFAULT_ANNOTATION_VALUE = "##default";


	private final XmlEventDecoder xmlEventDecoder = new XmlEventDecoder();

	private final JaxbContextContainer jaxbContexts = new JaxbContextContainer();

	private Function<Unmarshaller, Unmarshaller> unmarshallerProcessor = Function.identity();


	public Jaxb2XmlDecoder() {
		super(MimeTypeUtils.APPLICATION_XML, MimeTypeUtils.TEXT_XML);
	}


	
Configure a processor function to customize Unmarshaller instances.
Params:
processor – the function to use
Since:
5.1.3/**
	 * Configure a processor function to customize Unmarshaller instances.
	 * @param processor the function to use
	 * @since 5.1.3
	 */
	public void setUnmarshallerProcessor(Function<Unmarshaller, Unmarshaller> processor) {
		this.unmarshallerProcessor = this.unmarshallerProcessor.andThen(processor);
	}

	
Return the configured processor for customizing Unmarshaller instances.
Since:
5.1.3/**
	 * Return the configured processor for customizing Unmarshaller instances.
	 * @since 5.1.3
	 */
	public Function<Unmarshaller, Unmarshaller> getUnmarshallerProcessor() {
		return this.unmarshallerProcessor;
	}


	@Override
	public boolean canDecode(ResolvableType elementType, @Nullable MimeType mimeType) {
		Class<?> outputClass = elementType.toClass();
		return (outputClass.isAnnotationPresent(XmlRootElement.class) ||
				outputClass.isAnnotationPresent(XmlType.class)) && super.canDecode(elementType, mimeType);
	}

	@Override
	public Flux<Object> decode(Publisher<DataBuffer> inputStream, ResolvableType elementType,
			@Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {

		Flux<XMLEvent> xmlEventFlux = this.xmlEventDecoder.decode(
				inputStream, ResolvableType.forClass(XMLEvent.class), mimeType, hints);

		Class<?> outputClass = elementType.toClass();
		QName typeName = toQName(outputClass);
		Flux<List<XMLEvent>> splitEvents = split(xmlEventFlux, typeName);

		return splitEvents.map(events -> {
			Object value = unmarshal(events, outputClass);
			LogFormatUtils.traceDebug(logger, traceOn -> {
				String formatted = LogFormatUtils.formatValue(value, !traceOn);
				return Hints.getLogPrefix(hints) + "Decoded [" + formatted + "]";
			});
			return value;
		});
	}

	@Override
	public Mono<Object> decodeToMono(Publisher<DataBuffer> inputStream, ResolvableType elementType,
			@Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {

		return decode(inputStream, elementType, mimeType, hints).singleOrEmpty();
	}

	private Object unmarshal(List<XMLEvent> events, Class<?> outputClass) {
		try {
			Unmarshaller unmarshaller = initUnmarshaller(outputClass);
			XMLEventReader eventReader = StaxUtils.createXMLEventReader(events);
			if (outputClass.isAnnotationPresent(XmlRootElement.class)) {
				return unmarshaller.unmarshal(eventReader);
			}
			else {
				JAXBElement<?> jaxbElement = unmarshaller.unmarshal(eventReader, outputClass);
				return jaxbElement.getValue();
			}
		}
		catch (UnmarshalException ex) {
			throw new DecodingException("Could not unmarshal XML to " + outputClass, ex);
		}
		catch (JAXBException ex) {
			throw new CodecException("Invalid JAXB configuration", ex);
		}
	}

	private Unmarshaller initUnmarshaller(Class<?> outputClass) throws JAXBException {
		Unmarshaller unmarshaller = this.jaxbContexts.createUnmarshaller(outputClass);
		return this.unmarshallerProcessor.apply(unmarshaller);
	}

	
Returns the qualified name for the given class, according to the mapping rules
in the JAXB specification.
/**
	 * Returns the qualified name for the given class, according to the mapping rules
	 * in the JAXB specification.
	 */
	QName toQName(Class<?> outputClass) {
		String localPart;
		String namespaceUri;

		if (outputClass.isAnnotationPresent(XmlRootElement.class)) {
			XmlRootElement annotation = outputClass.getAnnotation(XmlRootElement.class);
			localPart = annotation.name();
			namespaceUri = annotation.namespace();
		}
		else if (outputClass.isAnnotationPresent(XmlType.class)) {
			XmlType annotation = outputClass.getAnnotation(XmlType.class);
			localPart = annotation.name();
			namespaceUri = annotation.namespace();
		}
		else {
			throw new IllegalArgumentException("Output class [" + outputClass.getName() +
					"] is neither annotated with @XmlRootElement nor @XmlType");
		}

		if (JAXB_DEFAULT_ANNOTATION_VALUE.equals(localPart)) {
			localPart = ClassUtils.getShortNameAsProperty(outputClass);
		}
		if (JAXB_DEFAULT_ANNOTATION_VALUE.equals(namespaceUri)) {
			Package outputClassPackage = outputClass.getPackage();
			if (outputClassPackage != null && outputClassPackage.isAnnotationPresent(XmlSchema.class)) {
				XmlSchema annotation = outputClassPackage.getAnnotation(XmlSchema.class);
				namespaceUri = annotation.namespace();
			}
			else {
				namespaceUri = XMLConstants.NULL_NS_URI;
			}
		}
		return new QName(namespaceUri, localPart);
	}

	
Split a flux of XMLEvents into a flux of XMLEvent lists, one list for each branch of the tree that starts with the given qualified name. That is, given the XMLEvents shown here, and the desiredName "child", this method returns a flux of two lists, each of which containing the events of a particular branch of the tree that starts with "child". 

The first list, dealing with the first branch of the tree:

StartElement child
Characters foo
EndElement child

The second list, dealing with the second branch of the tree:

StartElement child
Characters bar
EndElement child



/**
	 * Split a flux of {@link XMLEvent XMLEvents} into a flux of XMLEvent lists, one list
	 * for each branch of the tree that starts with the given qualified name.
	 * That is, given the XMLEvents shown {@linkplain XmlEventDecoder here},
	 * and the {@code desiredName} "{@code child}", this method returns a flux
	 * of two lists, each of which containing the events of a particular branch
	 * of the tree that starts with "{@code child}".
	 * <ol>
	 * <li>The first list, dealing with the first branch of the tree:
	 * <ol>
	 * <li>{@link javax.xml.stream.events.StartElement} {@code child}</li>
	 * <li>{@link javax.xml.stream.events.Characters} {@code foo}</li>
	 * <li>{@link javax.xml.stream.events.EndElement} {@code child}</li>
	 * </ol>
	 * <li>The second list, dealing with the second branch of the tree:
	 * <ol>
	 * <li>{@link javax.xml.stream.events.StartElement} {@code child}</li>
	 * <li>{@link javax.xml.stream.events.Characters} {@code bar}</li>
	 * <li>{@link javax.xml.stream.events.EndElement} {@code child}</li>
	 * </ol>
	 * </li>
	 * </ol>
	 */
	Flux<List<XMLEvent>> split(Flux<XMLEvent> xmlEventFlux, QName desiredName) {
		return xmlEventFlux.flatMap(new SplitFunction(desiredName));
	}


	private static class SplitFunction implements Function<XMLEvent, Publisher<? extends List<XMLEvent>>> {

		private final QName desiredName;

		@Nullable
		private List<XMLEvent> events;

		private int elementDepth = 0;

		private int barrier = Integer.MAX_VALUE;

		public SplitFunction(QName desiredName) {
			this.desiredName = desiredName;
		}

		@Override
		public Publisher<? extends List<XMLEvent>> apply(XMLEvent event) {
			if (event.isStartElement()) {
				if (this.barrier == Integer.MAX_VALUE) {
					QName startElementName = event.asStartElement().getName();
					if (this.desiredName.equals(startElementName)) {
						this.events = new ArrayList<>();
						this.barrier = this.elementDepth;
					}
				}
				this.elementDepth++;
			}
			if (this.elementDepth > this.barrier) {
				Assert.state(this.events != null, "No XMLEvent List");
				this.events.add(event);
			}
			if (event.isEndElement()) {
				this.elementDepth--;
				if (this.elementDepth == this.barrier) {
					this.barrier = Integer.MAX_VALUE;
					Assert.state(this.events != null, "No XMLEvent List");
					return Mono.just(this.events);
				}
			}
			return Mono.empty();
		}
	}

}