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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.parser.shiftreduce;

import java.util.Collection;

import edu.stanford.nlp.ling.CoreLabel;
import edu.stanford.nlp.parser.common.ParserConstraint;
import edu.stanford.nlp.trees.Tree;
import edu.stanford.nlp.trees.TreeCoreAnnotations;
import edu.stanford.nlp.util.ErasureUtils;

class ShiftReduceUtils {

  private ShiftReduceUtils() {} // static utility methods

  static BinaryTransition.Side getBinarySide(Tree tree) {
    if (tree.children().length != 2) {
      throw new AssertionError();
    }
    CoreLabel label = ErasureUtils.uncheckedCast(tree.label());
    CoreLabel childLabel = ErasureUtils.uncheckedCast(tree.children()[0].label());
    if (label.get(TreeCoreAnnotations.HeadWordLabelAnnotation.class) == childLabel.get(TreeCoreAnnotations.HeadWordLabelAnnotation.class)) {
      return BinaryTransition.Side.LEFT;
    } else {
      return BinaryTransition.Side.RIGHT;
    }
  }

  static boolean isTemporary(Tree tree) {
    String label = tree.value();
    return label.startsWith("@");
  }

  static boolean isEquivalentCategory(String l1, String l2) {
    if (l1.startsWith("@")) l1 = l1.substring(1);
    if (l2.startsWith("@")) l2 = l2.substring(1);
    return l1.equals(l2);
  }

  /** Returns a 0-based index of the head of the tree.  Assumes the leaves had been indexed from 1 */
  static int headIndex(Tree tree) {
    CoreLabel label = ErasureUtils.uncheckedCast(tree.label());
    CoreLabel headLabel = label.get(TreeCoreAnnotations.HeadWordLabelAnnotation.class);
    return headLabel.index() - 1;
  }

  /** Returns a 0-based index of the left leaf of the tree.  Assumes the leaves had been indexed from 1 */
  static int leftIndex(Tree tree) {
    if (tree.isLeaf()) {
      CoreLabel label = ErasureUtils.uncheckedCast(tree.label());
      return label.index() - 1;
    }

    return leftIndex(tree.children()[0]);
  }

  /** Returns a 0-based index of the right leaf of the tree.  Assumes the leaves had been indexed from 1 */
  static int rightIndex(Tree tree) {
    if (tree.isLeaf()) {
      CoreLabel label = ErasureUtils.uncheckedCast(tree.label());
      return label.index() - 1;
    }

    return rightIndex(tree.children()[tree.children().length - 1]);
  }

  static boolean constraintMatchesTreeTop(Tree top, ParserConstraint constraint) {
    while (true) {
      if (constraint.state.matcher(top.value()).matches()) {
        return true;
      } else if (top.children().length == 1) {
        top = top.children()[0];
      } else {
        return false;
      }
    }
  }

  /**
   * Returns true iff the given {@code state} is present on the {@code agenda}
   */
  static boolean findStateOnAgenda(Collection agenda, State state) {
    for (State other : agenda) {
      if (other.areTransitionsEqual(state)) {
        return true;
      }
    }
    return false;
  }

}