/*
 * Copyright 2017 Graz University of Technology EAAF-Core Components has been developed in a
 * cooperation between EGIZ, A-SIT Plus, A-SIT, and Graz University of Technology.
 *
 * Licensed under the EUPL, Version 1.2 or - as soon they will be approved by the European
 * Commission - subsequent versions of the EUPL (the "Licence"); You may not use this work except in
 * compliance with the Licence. You may obtain a copy of the Licence at:
 * https://joinup.ec.europa.eu/news/understanding-eupl-v12
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the Licence
 * is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the Licence for the specific language governing permissions and limitations under
 * the Licence.
 *
 * This product combines work with different licenses. See the "NOTICE" text file for details on the
 * various modules and licenses. The "NOTICE" text file is part of the distribution. Any derivative
 * works that you distribute must include a readable copy of the "NOTICE" text file.
*/

package at.gv.egiz.eaaf.core.impl.utils;

import java.io.InputStream;

import org.apache.xerces.util.URI;
import org.apache.xerces.util.URI.MalformedURIException;
import org.xml.sax.EntityResolver;
import org.xml.sax.InputSource;

import at.gv.egiz.eaaf.core.api.data.XmlNamespaceConstants;

/**
 * An <code>EntityResolver</code> that looks up entities stored as local
 * resources.
 *
 * <p>
 * The following DTDs are mapped to local resources:
 * <ul>
 * <li>The XMLSchema.dtd</li>
 * <li>The datatypes.dtd</li>
 * </ul>
 * </p>
 * </p>
 * For all other resources, an attempt is made to resolve them as resources,
 * either absolute or relative to <code>Constants.SCHEMA_ROOT</code>.
 *
 */
public class EaafDomEntityResolver implements EntityResolver {

  /**
   * Resolve an entity.
   * <p>
   * The <code>systemId</code> parameter is used to perform the lookup of the
   * entity as a resource, either by interpreting the <code>systemId</code> as an
   * absolute resource path, or by appending the last path component of
   * <code>systemId</code> to <code>Constants.SCHEMA_ROOT</code>.
   * </p>
   *
   * @param publicId The public ID of the resource.
   * @param systemId The system ID of the resource.
   * @return An <code>InputSource</code> from which the entity can be read, or
   *         <code>null</code>, if the entity could not be found.
   * @see org.xml.sax.EntityResolver#resolveEntity(java.lang.String,
   *      java.lang.String)
   */
  @Override
  public InputSource resolveEntity(final String publicId, String systemId) {
    InputStream stream;
    int slashPos;

    if (publicId != null) {
      // check if we can resolve some standard dtd's
      if (publicId.equalsIgnoreCase("-//W3C//DTD XMLSchema 200102//EN")) {
        return new InputSource(
            getClass().getResourceAsStream(XmlNamespaceConstants.SCHEMA_ROOT + "XMLSchema.dtd"));
      } else if (publicId.equalsIgnoreCase("datatypes")) {
        return new InputSource(
            getClass().getResourceAsStream(XmlNamespaceConstants.SCHEMA_ROOT + "datatypes.dtd"));
      }
    } else if (systemId != null) {
      // get the URI path
      try {
        final URI uri = new URI(systemId);
        systemId = uri.getPath();

        if (!"file".equals(uri.getScheme()) || "".equals(systemId.trim())) {
          return null;
        }

      } catch (final MalformedURIException e) {
        return null;
      }

      // try to get the resource from the full path
      stream = getClass().getResourceAsStream(systemId);
      if (stream != null) {
        final InputSource source = new InputSource(stream);

        source.setSystemId(systemId);
        return source;
      }

      // try to get the resource from the last path component
      slashPos = systemId.lastIndexOf('/');
      if (slashPos >= 0 && systemId.length() > slashPos) {
        systemId = systemId.substring(slashPos + 1, systemId.length());
        stream = getClass().getResourceAsStream(XmlNamespaceConstants.SCHEMA_ROOT + systemId);
        if (stream != null) {
          final InputSource source = new InputSource(stream);

          source.setSystemId(systemId);
          return source;
        }
      }
    }

    return null; // nothing found - let the parser handle the entity
  }
}