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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.Arrays;
import java.util.List;

import edu.stanford.nlp.parser.common.ParserConstraint;
import edu.stanford.nlp.trees.Tree;
import edu.stanford.nlp.util.TreeShapedStack;


/**
 * Transition that makes a compound unary parse node in a partially
 * finished tree.  It potentially adds multiple unary layers to the
 * current tree.
 *
 * @author John Bauer
 */
public class CompoundUnaryTransition implements Transition {
  /**
   * labels[0] is the top of the unary chain.
   * A unary chain that results in a ROOT will have labels[0] == ROOT, for example.
   */
  public final String[] labels;

  /** root transitions are illegal in the middle of the tree, naturally */
  public final boolean isRoot;

  public CompoundUnaryTransition(List labels, boolean isRoot) {
    this.labels = new String[labels.size()];
    for (int i = 0; i < labels.size(); ++i) {
      this.labels[i] = labels.get(i);
    }
    this.isRoot = isRoot;
  }

  /**
   * Legal as long as there is at least one item on the state's stack
   * and that item has not already been unary transformed.
   */
  public boolean isLegal(State state, List constraints) {
    if (state.finished) {
      return false;
    }
    if (state.stack.size() == 0) {
      return false;
    }
    final Tree top = state.stack.peek();
    if (top.children().length == 1 && !top.isPreTerminal()) {
      // Disallow unary transitions after we've already had a unary transition
      return false;
    }
    if (top.label().value().equals(labels[0])) {
      // Disallow unary transitions where the final label doesn't change
      return false;
    }
    // TODO: need to think more about when a unary transition is
    // allowed if the top of the stack is temporary
    if (top.label().value().startsWith("@") && !labels[labels.length - 1].equals(top.label().value().substring(1))) {
      // Disallow a transition if the top is a binarized node and the
      // bottom of the unary transition chain isn't the same type
      return false;
    }
    if (isRoot && (state.stack.size() > 1 || !state.endOfQueue())) {
      return false;
    }

    // Now we check the constraints...
    // Constraints only apply to CompoundUnaryTransitions if the tree
    // is exactly the right size and the tree has not already been
    // constructed to match the constraint.  In that case, we check to
    // see if the candidate transition contains the desired label.
    if (constraints == null) {
      return true;
    }

    for (ParserConstraint constraint : constraints) {
      if (ShiftReduceUtils.leftIndex(top) != constraint.start || ShiftReduceUtils.rightIndex(top) != constraint.end - 1) {
        continue;
      }
      if (constraint.state.matcher(top.value()).matches()) {
        continue;
      }
      boolean found = false;
      for (String label : labels) {
        if (constraint.state.matcher(label).matches()) {
          found = true;
          break;
        }
      }
      if (!found) {
        return false;
      }
    }

    return true;
  }

  /**
   * Add a unary node to the existing node on top of the stack
   */
  public State apply(State state) {
    return apply(state, 0.0);
  }

  /**
   * Add a unary node to the existing node on top of the stack
   */
  public State apply(State state, double scoreDelta) {
    Tree top = state.stack.peek();
    for (int i = labels.length - 1; i >= 0; --i) {
      top = UnaryTransition.addUnaryNode(top, labels[i]);
    }

    TreeShapedStack stack = state.stack.pop();
    stack = stack.push(top);
    return new State(stack, state.transitions.push(this), state.separators, state.sentence, state.tokenPosition, state.score + scoreDelta, false);
  }

  @Override
  public boolean equals(Object o) {
    if (o == this) {
      return true;
    }
    if (!(o instanceof CompoundUnaryTransition)) {
      return false;
    }
    String[] otherLabels = ((CompoundUnaryTransition) o).labels;
    return Arrays.equals(labels, otherLabels);
  }

  @Override
  public int hashCode() {
    return 29467607 ^ Arrays.hashCode(labels);
  }

  @Override
  public String toString() {
    return "CompoundUnary" + (isRoot ? "*" : "") + "(" + Arrays.asList(labels).toString() + ")";
  }

  private static final long serialVersionUID = 1;

}