SearchUtils.java

/**
 * 
 */
package com.xored.glance.internal.ui.search;

import java.util.regex.Pattern;
import java.util.regex.PatternSyntaxException;

/**
 * @author Yuri Strot
 * 
 */
public class SearchUtils {

	public static Pattern createPattern(String pattern, boolean caseSensitive,
			boolean regExSearch, boolean wordPrefix, boolean camelCase) {
		if (pattern == null || pattern.length() == 0)
			return null;

		int patternFlags = 0;

		if (!caseSensitive)
			patternFlags |= Pattern.CASE_INSENSITIVE | Pattern.UNICODE_CASE;

		if (regExSearch) {
			patternFlags |= Pattern.MULTILINE;
			pattern = substituteLinebreak(pattern);
		} else {
			RegExpBulder builder = camelCase ? new CamelCaseBuilder()
					: new RegExpBulder();
			pattern = asRegPattern(pattern, builder);
			if (wordPrefix) {
				pattern = "\\b" + pattern; //$NON-NLS-1$
			}
		}

		return Pattern.compile(pattern, patternFlags);
	}

	/**
	 * Substitutes \R in a regex find pattern with (?>\r\n?|\n)
	 * 
	 * @param findString
	 *            the original find pattern
	 * @return the transformed find pattern
	 * @throws PatternSyntaxException
	 *             if \R is added at an illegal position (e.g. in a character
	 *             set)
	 */
	private static String substituteLinebreak(String findString)
			throws PatternSyntaxException {
		int length = findString.length();
		StringBuffer buf = new StringBuffer(length);

		int inCharGroup = 0;
		int inBraces = 0;
		boolean inQuote = false;
		for (int i = 0; i < length; i++) {
			char ch = findString.charAt(i);
			switch (ch) {
			case '[':
				buf.append(ch);
				if (!inQuote)
					inCharGroup++;
				break;

			case ']':
				buf.append(ch);
				if (!inQuote)
					inCharGroup--;
				break;

			case '{':
				buf.append(ch);
				if (!inQuote && inCharGroup == 0)
					inBraces++;
				break;

			case '}':
				buf.append(ch);
				if (!inQuote && inCharGroup == 0)
					inBraces--;
				break;

			case '\\':
				if (i + 1 < length) {
					char ch1 = findString.charAt(i + 1);
					if (inQuote) {
						if (ch1 == 'E')
							inQuote = false;
						buf.append(ch).append(ch1);
						i++;

					} else if (ch1 == 'R') {
						if (inCharGroup > 0 || inBraces > 0) {
							throw new PatternSyntaxException(
									"Illegal position for \\R", findString, i);
						}
						buf.append("(?>\\r\\n?|\\n)"); //$NON-NLS-1$
						i++;

					} else {
						if (ch1 == 'Q') {
							inQuote = true;
						}
						buf.append(ch).append(ch1);
						i++;
					}
				} else {
					buf.append(ch);
				}
				break;

			default:
				buf.append(ch);
				break;
			}

		}
		return buf.toString();
	}

	/**
	 * Converts a non-regex string to a pattern that can be used with the regex
	 * search engine.
	 * 
	 * @param string
	 *            the non-regex pattern
	 * @return the string converted to a regex pattern
	 */
	private static String asRegPattern(String string, RegExpBulder builder) {
		StringBuffer out = new StringBuffer(string.length());
		boolean quoting = false;

		for (int i = 0, length = string.length(); i < length; i++) {
			char ch = string.charAt(i);
			String re = builder.asRegExp(ch);
			if (re != null) {
				if (quoting) {
					out.append("\\E"); //$NON-NLS-1$
					quoting = false;
				}
				out.append(re); //$NON-NLS-1$
				continue;
			}
			if (!quoting) {
				out.append("\\Q"); //$NON-NLS-1$
				quoting = true;
			}
			out.append(ch);
		}
		if (quoting)
			out.append("\\E"); //$NON-NLS-1$

		return out.toString();
	}

	private static class RegExpBulder {

		public String asRegExp(char ch) {
			if (ch == '\\') {
				return "\\\\";
			}
			return null;
		}

	}

	private static class CamelCaseBuilder extends RegExpBulder {

		@Override
		public String asRegExp(char ch) {
			String regExp = super.asRegExp(ch);
			if (regExp != null) {
				wordPrev = false;
			} else {
				boolean word = isWord(ch);
				if (word && wordPrev) {
					regExp = CAMEL_CASE_SKIP + ch;
				}
				wordPrev = word;
			}
			return regExp;
		}

		private boolean isWord(char ch) {
			return ch == '_' || Character.isLetterOrDigit(ch);
		}

		private boolean wordPrev = false;

	}

	private static final String CAMEL_CASE_SKIP = "\\w*";

}