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Stanford CoreNLP provides a set of natural language analysis tools which can take raw English language text input and give the base forms of words, their parts of speech, whether they are names of companies, people, etc., normalize dates, times, and numeric quantities, mark up the structure of sentences in terms of phrases and word dependencies, and indicate which noun phrases refer to the same entities. It provides the foundational building blocks for higher level text understanding applications.

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package edu.stanford.nlp.trees.ud;

import java.io.Reader;
import java.io.StringReader;
import java.util.*;
import java.util.function.Function;

import edu.stanford.nlp.international.Language;
import edu.stanford.nlp.ling.CoreAnnotations;
import edu.stanford.nlp.ling.IndexedWord;
import edu.stanford.nlp.objectbank.DelimitRegExIterator;
import edu.stanford.nlp.objectbank.IteratorFromReaderFactory;
import edu.stanford.nlp.objectbank.ObjectBank;
import edu.stanford.nlp.semgraph.SemanticGraph;
import edu.stanford.nlp.trees.GrammaticalRelation;
import edu.stanford.nlp.trees.TypedDependency;
import edu.stanford.nlp.util.IntPair;
import edu.stanford.nlp.util.Pair;

/**
 * Reader for ConLL-U formatted dependency treebanks.
 *
 * @author Sebastian Schuster
 */
public class CoNLLUDocumentReader implements
    IteratorFromReaderFactory {

  private static final String COMMENT_POS = "";

  private IteratorFromReaderFactory ifrf;

  public CoNLLUDocumentReader() {
    this.ifrf = DelimitRegExIterator.getFactory("\n(\\s*\n)+", new SentenceProcessor());
  }


  @Override
  public Iterator getIterator(Reader r) {
    return ifrf.getIterator(r);
  }


  private static final Comparator byIndex = (i1, i2) -> i1.compareTo(i2);

  /* Comparator for putting multiword tokens before regular tokens.  */
  private static final Comparator byType = (i1, i2) ->
          i1.containsKey(CoreAnnotations.CoNLLUTokenSpanAnnotation.class) ? -1 :
                  i2.containsKey(CoreAnnotations.CoNLLUTokenSpanAnnotation.class) ? 1 : 0;

  private static class SentenceProcessor implements Function {

    private int lineNumberCounter = 0;

    public SemanticGraph apply(String line) {
      if (line == null) return null;

      Function func = new WordProcessor();
      ObjectBank words = ObjectBank.getLineIterator(new StringReader(line), func);

      List wordList = new ArrayList<>(words);

      List sorted = new ArrayList<>(wordList.size());

      List comments = new LinkedList<>();

      /* Increase the line number in case there are comments before the actual sentence
       * and add them to the list of comments. */
      wordList.stream().filter(w -> w.tag() != null && w.tag().equals(COMMENT_POS))
              .forEach(w -> {
                lineNumberCounter++;
                comments.add(w.word());
              });

      wordList.stream().filter(w -> w.tag() == null || ! w.tag().equals(COMMENT_POS))
              .sorted(byIndex.thenComparing(byType))
              .forEach(w -> sorted.add(w));

      List sortedTokens = new ArrayList<>(wordList.size());
      sorted.stream()
              .filter(w -> !w.containsKey(CoreAnnotations.CoNLLUTokenSpanAnnotation.class))
              .forEach(w -> sortedTokens.add(w));

      /* Construct a semantic graph. */
      List deps = new ArrayList<>(sorted.size());

      IntPair tokenSpan = null;
      String originalToken = null;
      for (IndexedWord word : sorted) {
        lineNumberCounter++;

        if (word.containsKey(CoreAnnotations.CoNLLUTokenSpanAnnotation.class)) {
          tokenSpan = word.get(CoreAnnotations.CoNLLUTokenSpanAnnotation.class);
          originalToken = word.word();
        } else {
          /* Deal with multiword tokens. */
          if (tokenSpan != null && tokenSpan.getTarget() >= word.index()) {
            word.setOriginalText(originalToken);
            word.set(CoreAnnotations.CoNLLUTokenSpanAnnotation.class, tokenSpan);
          } else {
            tokenSpan = null;
            originalToken = null;
          }
          GrammaticalRelation reln = GrammaticalRelation.valueOf(Language.UniversalEnglish,
                  word.get(CoreAnnotations.CoNLLDepTypeAnnotation.class));
          int govIdx = word.get(CoreAnnotations.CoNLLDepParentIndexAnnotation.class);
          IndexedWord gov;
          if (govIdx == 0) {
            gov = new IndexedWord(word.docID(), word.sentIndex(), 0);
            gov.setValue("ROOT");
            if (word.get(CoreAnnotations.CoNLLDepTypeAnnotation.class).equals("root")) {
              reln = GrammaticalRelation.ROOT;
            }
          } else {
            gov = sortedTokens.get(govIdx - 1);
          }
          TypedDependency dep = new TypedDependency(reln, gov, word);
          word.set(CoreAnnotations.LineNumberAnnotation.class, lineNumberCounter);
          deps.add(dep);

          HashMap extraDeps = word.get(CoreAnnotations.CoNLLUSecondaryDepsAnnotation.class);
          for (Integer extraGovIdx : extraDeps.keySet()) {
            GrammaticalRelation extraReln =
                    GrammaticalRelation.valueOf(Language.UniversalEnglish, extraDeps.get(extraGovIdx));
            IndexedWord extraGov =  sortedTokens.get(extraGovIdx - 1);
            TypedDependency extraDep = new TypedDependency(extraReln, extraGov, word);
            extraDep.setExtra();
            deps.add(extraDep);
          }
        }
      }
      lineNumberCounter++;

      SemanticGraph sg = new SemanticGraph(deps);

      comments.forEach(c -> sg.addComment(c));

      return sg;
    }
  }

  private static class WordProcessor implements Function {
    public IndexedWord apply(String line) {


      IndexedWord word = new IndexedWord();
      if (line.startsWith("#")) {
        word.setWord(line);
        word.setTag(COMMENT_POS);
        return word;
      }


      String[] bits = line.split("\\s+");

      word.set(CoreAnnotations.TextAnnotation.class, bits[1]);

      /* Check if it is a multiword token. */
      if (bits[0].contains("-")) {
        String[] span = bits[0].split("-");
        Integer start = Integer.parseInt(span[0]);
        Integer end = Integer.parseInt(span[1]);
        word.set(CoreAnnotations.CoNLLUTokenSpanAnnotation.class, new IntPair(start, end));
        word.set(CoreAnnotations.IndexAnnotation.class, start);
      } else {
        word.set(CoreAnnotations.IndexAnnotation.class, Integer.parseInt(bits[0]));
        word.set(CoreAnnotations.LemmaAnnotation.class, bits[2]);
        word.set(CoreAnnotations.CoarseTagAnnotation.class, bits[3]);
        word.set(CoreAnnotations.PartOfSpeechAnnotation.class, bits[4]);

        word.set(CoreAnnotations.CoNLLDepParentIndexAnnotation.class, Integer.parseInt(bits[6]));
        word.set(CoreAnnotations.CoNLLDepTypeAnnotation.class, bits[7]);
        word.set(CoreAnnotations.CoNLLUMisc.class, bits[9]);

        word.setIndex(Integer.parseInt(bits[0]));
        word.setValue(bits[1]);

        /* Parse features. */
        HashMap features = CoNLLUUtils.parseFeatures(bits[5]);
        word.set(CoreAnnotations.CoNLLUFeats.class, features);

        /* Parse extra dependencies. */
        HashMap extraDeps = CoNLLUUtils.parseExtraDeps(bits[8]);
        word.set(CoreAnnotations.CoNLLUSecondaryDepsAnnotation.class, extraDeps);
      }

    return word;
    }
  }
}