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Text processing routines for Twitter Tweets
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// Copyright 2018 Twitter, Inc.
// Licensed under the Apache License, Version 2.0
// http://www.apache.org/licenses/LICENSE-2.0

package com.twitter.twittertext;

import java.text.CharacterIterator;
import java.text.StringCharacterIterator;
import java.util.List;

/**
 * A class for adding HTML highlighting in Tweet text (such as would be returned from a Search)
 */
public class HitHighlighter {
  /**
   * Default HTML tag for highlight hits
   */
  public static final String DEFAULT_HIGHLIGHT_TAG = "em";

  /**
   * the current HTML tag used for hit highlighting
   */
  protected String highlightTag;

  /**
   * Create a new HitHighlighter object.
   */
  public HitHighlighter() {
    highlightTag = DEFAULT_HIGHLIGHT_TAG;
  }

  /**
   * Surround the hits in the provided text with an HTML tag.
   * This is used with offsets from the search API to support the highlighting of query terms.
   *
   * @param text of the Tweet to highlight
   * @param hits A List of highlighting offsets (themselves lists of two elements)
   * @return text with highlight HTML added
   */
  public String highlight(String text, List> hits) {
    if (hits == null || hits.isEmpty()) {
      return text;
    }

    final StringBuilder sb = new StringBuilder(text.length());
    final CharacterIterator iterator = new StringCharacterIterator(text);
    boolean isCounting = true;
    boolean tagOpened = false;
    int currentIndex = 0;
    char currentChar = iterator.first();

    while (currentChar != CharacterIterator.DONE) {
      // TODO: this is slow.
      for (List startEnd : hits) {
        if (startEnd.get(0) == currentIndex) {
          sb.append(tag(false));
          tagOpened = true;
        } else if (startEnd.get(1) == currentIndex) {
          sb.append(tag(true));
          tagOpened = false;
        }
      }

      if (currentChar == '<') {
        isCounting = false;
      } else if (currentChar == '>' && !isCounting) {
        isCounting = true;
      }

      if (isCounting) {
        currentIndex++;
      }
      sb.append(currentChar);
      currentChar = iterator.next();
    }

    if (tagOpened) {
      sb.append(tag(true));
    }

    return sb.toString();
  }

  /**
   * Format the current highlightTag by adding < and >.
   * If closeTag is true then the tag returned will include a
   * / to signify a closing tag.
   *
   * @param closeTag true if this is a closing tag, false otherwise
   * @return reformed tag
   */
  protected String tag(boolean closeTag) {
    final StringBuilder sb = new StringBuilder(highlightTag.length() + 3);
    sb.append("<");
    if (closeTag) {
      sb.append("/");
    }
    sb.append(highlightTag).append(">");
    return sb.toString();
  }

  /**
   * Get the current HTML tag used for phrase highlighting.
   *
   * @return current HTML tag (without < or >)
   */
  public String getHighlightTag() {
    return highlightTag;
  }

  /**
   * Set the current HTML tag used for phrase highlighting.
   *
   * @param highlightTag sets highlighting tag
   */
  public void setHighlightTag(String highlightTag) {
    this.highlightTag = highlightTag;
  }
}