/*
 * 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.update.processor;

import java.lang.invoke.MethodHandles;
import java.util.ArrayList;
import java.util.List;

import org.apache.solr.request.SolrQueryRequest;
import org.apache.solr.response.SolrQueryResponse;
import org.apache.tika.language.LanguageIdentifier;

import org.apache.solr.common.SolrInputDocument;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.Collection;

/**
 * Identifies the language of a set of input fields using Tika's
 * LanguageIdentifier.
 * The tika-core-x.y.jar must be on the classpath
 * <p>
 * See <a href="http://wiki.apache.org/solr/LanguageDetection">http://wiki.apache.org/solr/LanguageDetection</a>
 * @since 3.5
 */
public class TikaLanguageIdentifierUpdateProcessor extends LanguageIdentifierUpdateProcessor {

  private static final Logger log = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());

  public TikaLanguageIdentifierUpdateProcessor(SolrQueryRequest req,
      SolrQueryResponse rsp, UpdateRequestProcessor next) {
    super(req, rsp, next);
  }
  
  @Override
  protected List<DetectedLanguage> detectLanguage(SolrInputDocument doc) {
    List<DetectedLanguage> languages = new ArrayList<>();
    String content = concatFields(doc);
    if (content.length() != 0) {
      LanguageIdentifier identifier = new LanguageIdentifier(content);
      // FIXME: Hack - we get the distance from toString and calculate our own certainty score
      Double distance = Double.parseDouble(tikaSimilarityPattern.matcher(identifier.toString()).replaceFirst("$1"));
      // This formula gives: 0.02 => 0.8, 0.1 => 0.5 which is a better sweetspot than isReasonablyCertain()
      Double certainty = 1 - (5 * distance);
      if (certainty < 0)
        certainty = 0d;
      DetectedLanguage language = new DetectedLanguage(identifier.getLanguage(), certainty);
      languages.add(language);
      log.debug("Language detected as "+language+" with a certainty of "+language.getCertainty()+" (Tika distance="+identifier.toString()+")");
    } else {
      log.debug("No input text to detect language from, returning empty list");
    }
    return languages;
  }


  /**
   * Concatenates content from multiple fields
   */
  protected String concatFields(SolrInputDocument doc) {
    StringBuilder sb = new StringBuilder(getExpectedSize(doc, inputFields));
    for (String fieldName : inputFields) {
      log.debug("Appending field " + fieldName);
      if (doc.containsKey(fieldName)) {
        Collection<Object> fieldValues = doc.getFieldValues(fieldName);
        if (fieldValues != null) {
          for (Object content : fieldValues) {
            if (content instanceof String) {
              String stringContent = (String) content;
              if (stringContent.length() > maxFieldValueChars) {
                sb.append(stringContent.substring(0, maxFieldValueChars));
              } else {
                sb.append(stringContent);
}
              sb.append(" ");
              if (sb.length() > maxTotalChars) {
                sb.setLength(maxTotalChars);
                break;
              }
            } else {
              log.warn("Field " + fieldName + " not a String value, not including in detection");
            }
          }
        }
      }
    }
    return sb.toString();
  }

  /**
   * Calculate expected string size.
   *
   * @param doc           solr input document
   * @param fields        fields to select
   * @return expected size of string value
   */
  private int getExpectedSize(SolrInputDocument doc, String[] fields) {
    int docSize = 0;
    for (String field : fields) {
      Collection<Object> contents = doc.getFieldValues(field);
      for (Object content : contents) {
        if (content instanceof String) {
          docSize += Math.min(((String) content).length(), maxFieldValueChars);
        }
      }
      docSize = Math.min(docSize, maxTotalChars);
    }
    return docSize;
  }
}