HitHighlighter.java

package com.twitter;

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;
	}

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

	/**
	 * Surround the <code>hits</code> in the provided <code>text</code> with an
	 * HTML tag. This is used with offsets from the base_dual_pane 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(final String text, final List<List<Integer>> 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 (final List<Integer> start_end : hits) {
				if (start_end.get(0) == currentIndex) {
					sb.append(tag(false));
					tagOpened = true;
				} else if (start_end.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();
	}

	/**
	 * Set the current HTML tag used for phrase highlighting.
	 * 
	 * @param new HTML tag (without < or >)
	 */
	public void setHighlightTag(final String highlightTag) {
		this.highlightTag = highlightTag;
	}

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