/*
    * Copyright 2019 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.bremersee.http.codec.xml;
  
  import java.util.ArrayList;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Map;
  import java.util.function.BiConsumer;
  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.XMLInputFactory;
  import javax.xml.stream.XMLStreamException;
  import javax.xml.stream.events.XMLEvent;
  import org.bremersee.xml.JaxbContextBuilder;
  import org.reactivestreams.Publisher;
  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.io.buffer.DataBufferLimitException;
  import org.springframework.core.io.buffer.DataBufferUtils;
  import org.springframework.core.log.LogFormatUtils;
  import org.springframework.http.MediaType;
  import org.springframework.http.codec.xml.XmlEventDecoder;
  import org.springframework.lang.NonNull;
  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;
  import org.springframework.validation.annotation.Validated;
  import reactor.core.Exceptions;
  import reactor.core.publisher.Flux;
  import reactor.core.publisher.Mono;
  import reactor.core.publisher.SynchronousSink;
  
  /**
   * Decode from a bytes stream containing XML elements to a stream of {@code Object}s (POJOs).
   *
   * <p>The decoding parts are taken from {@link org.springframework.http.codec.xml.Jaxb2XmlDecoder}.
   *
   * @author Sebastien Deleuze
   * @author Arjen Poutsma
   * @author Christian Bremer
   */
  @Validated
  public class ReactiveJaxbDecoder extends AbstractDecoder<Object> {
  
    /**
     * 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 static final XMLInputFactory inputFactory = StaxUtils.createDefensiveInputFactory();
  
  
    private final XmlEventDecoder xmlEventDecoder = new XmlEventDecoder();
  
    private final JaxbContextBuilder jaxbContextBuilder;
  
    private int maxInMemorySize = 256 * 1024;
  
    /**
     * Instantiates a new reactive jaxb decoder.
     *
     * @param jaxbContextBuilder the jaxb context builder
     */
    public ReactiveJaxbDecoder(final JaxbContextBuilder jaxbContextBuilder) {
     super(MimeTypeUtils.APPLICATION_XML, MimeTypeUtils.TEXT_XML,
         new MediaType("application", "*+xml"));
     this.jaxbContextBuilder = jaxbContextBuilder != null
         ? jaxbContextBuilder
         : JaxbContextBuilder.builder()
             .withCanUnmarshal(JaxbContextBuilder.CAN_UNMARSHAL_ALL);
   }
 
   /**
    * Set the max number of bytes that can be buffered by this decoder. This is either the size of the entire input when
    * decoding as a whole, or when using async parsing with Aalto XML, it is the size of one top-level XML tree. When the
    * limit is exceeded, {@link DataBufferLimitException} is raised.
    *
    * <p>By default this is set to 256K.
    *
    * @param byteCount the max number of bytes to buffer, or -1 for unlimited
    */
   public void setMaxInMemorySize(int byteCount) {
     this.maxInMemorySize = byteCount;
     this.xmlEventDecoder.setMaxInMemorySize(byteCount);
   }
 
   /**
    * Return the {@link #setMaxInMemorySize configured} byte count limit.
    *
    * @return the max in memory size
    */
   public int getMaxInMemorySize() {
     return this.maxInMemorySize;
   }
 
 
   @Override
   public boolean canDecode(@NonNull ResolvableType elementType, @Nullable MimeType mimeType) {
     if (super.canDecode(elementType, mimeType)) {
       final Class<?> outputClass = elementType.getRawClass();
       return jaxbContextBuilder.canUnmarshal(outputClass);
     } else {
       return false;
     }
   }
 
   @NonNull
   @Override
   public Flux<Object> decode(@NonNull 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;
     });
   }
 
   @NonNull
   @Override
   @SuppressWarnings({"rawtypes", "unchecked", "cast"})
   // XMLEventReader is Iterator<Object> on JDK 9
   public Object decode(DataBuffer dataBuffer, ResolvableType targetType,
       @Nullable MimeType mimeType, @Nullable Map<String, Object> hints) throws DecodingException {
 
     try {
       Iterator eventReader = inputFactory.createXMLEventReader(dataBuffer.asInputStream());
       List<XMLEvent> events = new ArrayList<>();
       eventReader.forEachRemaining(event -> events.add((XMLEvent) event));
       return unmarshal(events, targetType.toClass());
     } catch (XMLStreamException ex) {
       throw Exceptions.propagate(ex);
     } finally {
       DataBufferUtils.release(dataBuffer);
     }
   }
 
   @NonNull
   @Override
   public Mono<Object> decodeToMono(@NonNull Publisher<DataBuffer> input, @NonNull ResolvableType elementType,
       @Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {
 
     //noinspection NullableInLambdaInTransform
     return DataBufferUtils.join(input, this.maxInMemorySize)
         .map(dataBuffer -> decode(dataBuffer, elementType, mimeType, hints));
   }
 
   private Object unmarshal(List<XMLEvent> events, Class<?> outputClass) {
     try {
       Unmarshaller unmarshaller = jaxbContextBuilder.buildUnmarshaller(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);
     }
   }
 
   /**
    * Returns the qualified name for the given class, according to the mapping rules in the JAXB specification.
    *
    * @param outputClass the output class
    * @return the q name
    */
   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 {@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>
    *
    * @param xmlEventFlux the xml event as flux
    * @param desiredName the desired name
    * @return the list of xml events as flux
    */
   Flux<List<XMLEvent>> split(Flux<XMLEvent> xmlEventFlux, QName desiredName) {
     return xmlEventFlux.handle(new SplitHandler(desiredName));
   }
 
 
   private static class SplitHandler implements
       BiConsumer<XMLEvent, SynchronousSink<List<XMLEvent>>> {
 
     private final QName desiredName;
 
     private List<XMLEvent> events;
 
     private int elementDepth = 0;
 
     private int barrier = Integer.MAX_VALUE;
 
     /**
      * Instantiates a new split handler.
      *
      * @param desiredName the desired name
      */
     public SplitHandler(QName desiredName) {
       this.desiredName = desiredName;
     }
 
     @Override
     public void accept(XMLEvent event, SynchronousSink<List<XMLEvent>> sink) {
       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");
           sink.next(this.events);
         }
       }
     }
   }
 
 }