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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.solr.scripting.xslt;

import static org.apache.solr.scripting.xslt.XSLTConstants.TR;
import static org.apache.solr.scripting.xslt.XSLTConstants.XSLT_CACHE_DEFAULT;
import static org.apache.solr.scripting.xslt.XSLTConstants.XSLT_CACHE_PARAM;

import java.io.BufferedReader;
import java.io.CharArrayReader;
import java.io.CharArrayWriter;
import java.io.IOException;
import java.io.Reader;
import java.io.Writer;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerException;
import javax.xml.transform.stream.StreamResult;
import javax.xml.transform.stream.StreamSource;
import org.apache.solr.common.params.SolrParams;
import org.apache.solr.common.util.NamedList;
import org.apache.solr.request.SolrQueryRequest;
import org.apache.solr.response.QueryResponseWriter;
import org.apache.solr.response.SolrQueryResponse;
import org.apache.solr.response.XMLWriter;

/**
 * Customize the format of your search results via XSL stylesheet applied to the default XML
 * response format.
 *
 * QueryResponseWriter captures the output of the XMLWriter (in memory for now, not optimal
 * performance-wise), and applies an XSLT transform to it.
 */
public class XSLTResponseWriter implements QueryResponseWriter {
  public static final String DEFAULT_CONTENT_TYPE = "application/xml";

  private Integer xsltCacheLifetimeSeconds = null;

  @Override
  public void init(NamedList n) {
    final SolrParams p = n.toSolrParams();
    xsltCacheLifetimeSeconds = p.getInt(XSLT_CACHE_PARAM, XSLT_CACHE_DEFAULT);
  }

  @Override
  public String getContentType(SolrQueryRequest request, SolrQueryResponse response) {
    Transformer t = null;
    try {
      t = getTransformer(request);
    } catch (Exception e) {
      // TODO should our parent interface throw (IO)Exception?
      throw new RuntimeException("getTransformer fails in getContentType", e);
    }

    String mediaType = t.getOutputProperty("media-type");
    if (mediaType == null || mediaType.length() == 0) {
      // This did not happen in my tests, mediaTypeFromXslt is set to "text/xml"
      // if the XSLT transform does not contain an xsl:output element. Not sure
      // if this is standard behavior or if it's just my JVM/libraries
      mediaType = DEFAULT_CONTENT_TYPE;
    }

    if (!mediaType.contains("charset")) {
      String encoding = t.getOutputProperty("encoding");
      if (encoding == null || encoding.length() == 0) {
        encoding = "UTF-8";
      }
      mediaType = mediaType + "; charset=" + encoding;
    }

    return mediaType;
  }

  @Override
  public void write(Writer writer, SolrQueryRequest request, SolrQueryResponse response)
      throws IOException {
    final Transformer t = getTransformer(request);

    // capture the output of the XMLWriter
    final CharArrayWriter w = new CharArrayWriter();
    XMLWriter.writeResponse(w, request, response);

    // and write transformed result to our writer
    final Reader r = new BufferedReader(new CharArrayReader(w.toCharArray()));
    final StreamSource source = new StreamSource(r);
    final StreamResult result = new StreamResult(writer);
    try {
      t.transform(source, result);
    } catch (TransformerException te) {
      throw new IOException("XSLT transformation error", te);
    }
  }

  protected Transformer getTransformer(SolrQueryRequest request) throws IOException {
    final String xslt = request.getParams().required().get(TR);
    return TransformerProvider.getTransformer(request, xslt, xsltCacheLifetimeSeconds);
  }
}