/*
    * SPDX-FileCopyrightText: none
    * SPDX-License-Identifier: CC0-1.0
    */
   
   package gov.nist.secauto.metaschema.databind.io;
   
   import com.ctc.wstx.stax.WstxInputFactory;
   import com.fasterxml.jackson.core.JsonParser;
  import com.fasterxml.jackson.core.JsonToken;
  import com.fasterxml.jackson.core.io.MergedStream;
  import com.fasterxml.jackson.dataformat.yaml.YAMLFactory;
  
  import gov.nist.secauto.metaschema.core.configuration.DefaultConfiguration;
  import gov.nist.secauto.metaschema.core.configuration.IConfiguration;
  import gov.nist.secauto.metaschema.core.model.IBoundObject;
  import gov.nist.secauto.metaschema.core.model.util.JsonUtil;
  import gov.nist.secauto.metaschema.core.util.ObjectUtils;
  import gov.nist.secauto.metaschema.databind.IBindingContext;
  import gov.nist.secauto.metaschema.databind.io.json.JsonFactoryFactory;
  import gov.nist.secauto.metaschema.databind.io.yaml.impl.YamlFactoryFactory;
  
  import org.codehaus.stax2.XMLEventReader2;
  import org.codehaus.stax2.XMLInputFactory2;
  import org.eclipse.jdt.annotation.NotOwning;
  import org.eclipse.jdt.annotation.Owning;
  
  import java.io.ByteArrayInputStream;
  import java.io.Closeable;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InputStreamReader;
  import java.io.Reader;
  import java.nio.charset.Charset;
  
  import javax.xml.namespace.QName;
  import javax.xml.stream.XMLInputFactory;
  import javax.xml.stream.XMLStreamException;
  import javax.xml.stream.events.StartElement;
  
  import edu.umd.cs.findbugs.annotations.NonNull;
  import edu.umd.cs.findbugs.annotations.Nullable;
  
  /**
   * Provides a means to analyze content to determine what type of bound data it
   * contains.
   */
  public class ModelDetector {
    @NonNull
    private final IBindingContext bindingContext;
    @NonNull
    private final IConfiguration<DeserializationFeature<?>> configuration;
  
    /**
     * Construct a new format detector using the default configuration.
     *
     * @param bindingContext
     *          information about how Java classes are bound to Module definitions
     */
    public ModelDetector(
        @NonNull IBindingContext bindingContext) {
      this(bindingContext, new DefaultConfiguration<>());
    }
  
    /**
     * Construct a new format detector using the provided {@code configuration}.
     *
     * @param bindingContext
     *          information about how Java classes are bound to Module definitions
     * @param configuration
     *          the deserialization configuration
     */
    public ModelDetector(
        @NonNull IBindingContext bindingContext,
        @NonNull IConfiguration<DeserializationFeature<?>> configuration) {
      this.bindingContext = bindingContext;
      this.configuration = configuration;
    }
  
    private int getLookaheadLimit() {
      return configuration.get(DeserializationFeature.FORMAT_DETECTION_LOOKAHEAD_LIMIT);
    }
  
    @NonNull
    private IBindingContext getBindingContext() {
      return bindingContext;
    }
  
    @NonNull
    private IConfiguration<DeserializationFeature<?>> getConfiguration() {
      return configuration;
    }
  
    /**
     * Analyzes the data from the provided {@code inputStream} to determine it's
     * model.
     *
     * @param inputStream
     *          the resource stream to analyze
    * @param format
    *          the expected format of the data to read
    * @return the analysis result
    * @throws IOException
    *           if an error occurred while reading the resource
    */
   @NonNull
   @Owning
   public Result detect(@NonNull @NotOwning InputStream inputStream, @NonNull Format format)
       throws IOException {
     byte[] buf = ObjectUtils.notNull(inputStream.readNBytes(getLookaheadLimit()));
 
     Class<? extends IBoundObject> clazz;
     try (InputStream bis = new ByteArrayInputStream(buf)) {
       assert bis != null;
       switch (format) {
       case JSON:
         try (JsonParser parser = JsonFactoryFactory.instance().createParser(bis)) {
           assert parser != null;
           clazz = detectModelJsonClass(parser);
         }
         break;
       case YAML:
         YAMLFactory factory = YamlFactoryFactory.newParserFactoryInstance(getConfiguration());
         try (JsonParser parser = factory.createParser(bis)) {
           assert parser != null;
           clazz = detectModelJsonClass(parser);
         }
         break;
       case XML:
         clazz = detectModelXmlClass(bis);
         break;
       default:
         throw new UnsupportedOperationException(
             String.format("The format '%s' dataStream not supported", format));
       }
     }
 
     if (clazz == null) {
       throw new IllegalStateException(
           String.format("Detected format '%s', but unable to detect the bound data type", format.name()));
     }
 
     return new Result(clazz, inputStream, buf);
   }
 
   @NonNull
   private Class<? extends IBoundObject> detectModelXmlClass(@NonNull InputStream is) throws IOException {
     QName startElementQName;
     try {
       XMLInputFactory2 xmlInputFactory = (XMLInputFactory2) XMLInputFactory.newInstance();
       assert xmlInputFactory instanceof WstxInputFactory;
       xmlInputFactory.configureForXmlConformance();
       xmlInputFactory.setProperty(XMLInputFactory.IS_COALESCING, false);
 
       Reader reader = new InputStreamReader(is, Charset.forName("UTF8"));
       XMLEventReader2 eventReader = (XMLEventReader2) xmlInputFactory.createXMLEventReader(reader);
       while (eventReader.hasNext() && !eventReader.peek().isStartElement()) {
         eventReader.nextEvent();
       }
 
       if (!eventReader.peek().isStartElement()) {
         throw new IOException("Unable to detect a start element");
       }
 
       StartElement start = eventReader.nextEvent().asStartElement();
       startElementQName = ObjectUtils.notNull(start.getName());
     } catch (XMLStreamException ex) {
       throw new IOException(ex);
     }
 
     Class<? extends IBoundObject> clazz = getBindingContext().getBoundClassForRootXmlQName(startElementQName);
     if (clazz == null) {
       throw new IOException("Unrecognized element name: " + startElementQName.toString());
     }
     return clazz;
   }
 
   @Nullable
   private Class<? extends IBoundObject> detectModelJsonClass(@NonNull JsonParser parser) throws IOException {
     Class<? extends IBoundObject> retval = null;
     JsonUtil.advanceAndAssert(parser, JsonToken.START_OBJECT);
     outer: while (JsonToken.FIELD_NAME.equals(parser.nextToken())) {
       String name = ObjectUtils.notNull(parser.currentName());
       if (!"$schema".equals(name)) {
         IBindingContext bindingContext = getBindingContext();
         retval = bindingContext.getBoundClassForRootJsonName(name);
         break outer;
       }
       // do nothing
       parser.nextToken();
       // JsonUtil.skipNextValue(parser);
     }
     return retval;
   }
 
   public static final class Result implements Closeable {
     @NonNull
     private final Class<? extends IBoundObject> boundClass;
     @Owning
     private InputStream dataStream;
 
     private Result(
         @NonNull Class<? extends IBoundObject> clazz,
         @NonNull InputStream is,
         @NonNull byte[] buf) {
       this.boundClass = clazz;
       this.dataStream = new MergedStream(null, is, buf, 0, buf.length);
     }
 
     /**
      * Get the Java class representing the detected bound object.
      *
      * @return the Java class
      */
     @NonNull
     public Class<? extends IBoundObject> getBoundClass() {
       return boundClass;
     }
 
     /**
      * Get an {@link InputStream} that can be used to read the analyzed data from
      * the start.
      *
      * @return the stream
      */
     @NonNull
     @Owning
     public InputStream getDataStream() {
       return ObjectUtils.requireNonNull(dataStream, "data stream already closed");
     }
 
     @Override
     public void close() throws IOException {
       this.dataStream.close();
       this.dataStream = null;
     }
   }
 }