/*
 * Portions of this software was developed by employees of the National Institute
 * of Standards and Technology (NIST), an agency of the Federal Government and is
 * being made available as a public service. Pursuant to title 17 United States
 * Code Section 105, works of NIST employees are not subject to copyright
 * protection in the United States. This software may be subject to foreign
 * copyright. Permission in the United States and in foreign countries, to the
 * extent that NIST may hold copyright, to use, copy, modify, create derivative
 * works, and distribute this software and its documentation without fee is hereby
 * granted on a non-exclusive basis, provided that this notice and disclaimer
 * of warranty appears in all copies.
 *
 * THE SOFTWARE IS PROVIDED 'AS IS' WITHOUT ANY WARRANTY OF ANY KIND, EITHER
 * EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING, BUT NOT LIMITED TO, ANY WARRANTY
 * THAT THE SOFTWARE WILL CONFORM TO SPECIFICATIONS, ANY IMPLIED WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND FREEDOM FROM
 * INFRINGEMENT, AND ANY WARRANTY THAT THE DOCUMENTATION WILL CONFORM TO THE
 * SOFTWARE, OR ANY WARRANTY THAT THE SOFTWARE WILL BE ERROR FREE.  IN NO EVENT
 * SHALL NIST BE LIABLE FOR ANY DAMAGES, INCLUDING, BUT NOT LIMITED TO, DIRECT,
 * INDIRECT, SPECIAL OR CONSEQUENTIAL DAMAGES, ARISING OUT OF, RESULTING FROM,
 * OR IN ANY WAY CONNECTED WITH THIS SOFTWARE, WHETHER OR NOT BASED UPON WARRANTY,
 * CONTRACT, TORT, OR OTHERWISE, WHETHER OR NOT INJURY WAS SUSTAINED BY PERSONS OR
 * PROPERTY OR OTHERWISE, AND WHETHER OR NOT LOSS WAS SUSTAINED FROM, OR AROSE OUT
 * OF THE RESULTS OF, OR USE OF, THE SOFTWARE OR SERVICES PROVIDED HEREUNDER.
 */

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.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 java.io.ByteArrayInputStream;
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
  public Result detect(@NonNull InputStream inputStream, @NonNull Format format)
      throws IOException {
    byte[] buf = ObjectUtils.notNull(inputStream.readNBytes(getLookaheadLimit()));

    Class<?> clazz;
    try (InputStream bis = new ByteArrayInputStream(buf)) {
      switch (format) {
      case JSON:
        clazz = detectModelJsonClass(ObjectUtils.notNull(
            JsonFactoryFactory.instance().createParser(bis)));
        break;
      case YAML:
        YAMLFactory factory = YamlFactoryFactory.newParserFactoryInstance(getConfiguration());
        clazz = detectModelJsonClass(ObjectUtils.notNull(factory.createParser(bis)));
        break;
      case XML:
        clazz = detectModelXmlClass(ObjectUtils.notNull(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<?> 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<?> clazz = getBindingContext().getBoundClassForXmlQName(startElementQName);

    if (clazz == null) {
      throw new IOException("Unrecognized element name: " + startElementQName.toString());
    }
    return clazz;
  }

  @Nullable
  private Class<?> detectModelJsonClass(@NonNull JsonParser parser) throws IOException {
    Class<?> retval = null;
    JsonUtil.advanceAndAssert(parser, JsonToken.START_OBJECT);
    outer: while (JsonToken.FIELD_NAME.equals(parser.nextToken())) {
      String name = ObjectUtils.notNull(parser.getCurrentName());
      if ("$schema".equals(name)) {
        // do nothing
        parser.nextToken();
        // JsonUtil.skipNextValue(parser);
      } else {
        retval = getBindingContext().getBoundClassForJsonName(name);
        break outer;
      }
    }
    return retval;
  }

  public static class Result {
    @NonNull
    private final Class<?> boundClass;
    @NonNull
    private final InputStream dataStream;

    private Result(
        @NonNull Class<?> 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<?> getBoundClass() {
      return boundClass;
    }

    /**
     * Get an {@link InputStream} that can be used to read the analyzed data from
     * the start.
     *
     * @return the stream
     */
    @NonNull
    public InputStream getDataStream() {
      return dataStream;
    }
  }
}