package bjc.utils.parserutils;

import java.util.regex.Pattern;

/**
 * Split a string and keep given delimiters.
 *
 * @author Ben Culkin
 */
public class TokenSplitter {
	/*
	 * This string is a format template for the delimiter matching regex
	 *
	 * It does two things:
	 * 
	 * <ol>
	 * <li> Match to the left of the provided delimiter by positive lookahead </li>
	 * <li> Match to the right of the provided delimiter by positive lookbehind </li>
	 * </ol>
	 *
	 * Thus, it will only match in places where the delimiter is, but won't
	 * actually match the delimiter, leaving split to put it into the stream
	 */
	private static String WITH_DELIM = "(?:(?<=%1$s)|(?=%1$s))";

	/*
	 * This string is a format template for the multi-delimiter matching
	 * regex.
	 *
	 * It does the same thing as the single delimiter regex, but has to have
	 * some negative lookahead/lookbehind assertions to avoid splitting a
	 * delimiter into pieces.
	 */
	private static String WITH_MULTI_DELIM = "(?:(?<=%1$s+)(?!%1$s)|(?<!%1$s)(?=%1$s+))";

	/*
	 * These represent the internal state of the splitter.
	 */
	private StringBuilder	currPatt;
	private StringBuilder	currExclusionPatt;

	/*
	 * These represent the external state of the splitter.
	 *
	 * Compilation causes internal to become external.
	 */
	private Pattern	compPatt;
	private Pattern	exclusionPatt;

	/**
	 * Create a new token splitter.
	 */
	public TokenSplitter() {
	}

	/**
	 * Split a provided string using configured delimiters, and keeping the
	 * delimiters.
	 *
	 * <p>
	 * The splitter must be compiled first.
	 * </p>
	 * 
	 * @param inp
	 *                The string to split.
	 *
	 * @return The split string, including delimiters.
	 *
	 * @throws IllegalStateException
	 *                 If the splitter isn't compiled.
	 */
	public String[] split(String inp) {
		if(compPatt == null) throw new IllegalStateException("Token splitter has not been compiled yet");

		/*
		 * Don't split something that we should exclude from being split.
		 */
		if(exclusionPatt.matcher(inp).matches()) return new String[] { inp };

		return compPatt.split(inp);
	}

	/**
	 * Adds one or more strings as matched delimiters to split on.
	 *
	 * Only works for fixed length delimiters.
	 *
	 * The provided strings are regex-escaped before being used.
	 *
	 * @param delims
	 *                The delimiters to match on.
	 */
	public void addDelimiter(String... delims) {
		for(String delim : delims) {
			String quoteDelim = Pattern.quote(delim);
			String delimPat   = String.format(WITH_DELIM, quoteDelim);
	
			if(currPatt == null) {
				currPatt          = new StringBuilder();
				currExclusionPatt = new StringBuilder();
	
				currPatt.append("(?:" + delimPat + ")");
				currExclusionPatt.append("(?:" + quoteDelim + ")");
			} else {
				currPatt.append("|(?:" + delimPat + ")");
				currExclusionPatt.append("|(?:" + quoteDelim + ")");
			}
		}
	}

	/**
	 * Adds a character class as a matched delimiter to split on.
	 *
	 * The provided string should be a pattern to match one or more
	 * occurances of.
	 *
	 * @param delim
	 *                The delimiter to split on.
	 */
	public void addMultiDelimiter(String delim) {
		String delimPat = String.format(WITH_MULTI_DELIM, "(?:" + delim + ")");

		if(currPatt == null) {
			currPatt          = new StringBuilder();
			currExclusionPatt = new StringBuilder();

			currPatt.append("(?:" + delimPat + ")");
			currExclusionPatt.append("(?:(?:" + delim + ")+)");

		} else {
			currPatt.append("|(?:" + delimPat + ")");
			currExclusionPatt.append("|(?:(?:" + delim + ")+)");
		}
	}

	/**
	 * Marks strings matching the pattern delim as non-splittable.
	 *
	 * @param delim
	 * 		The regex to not splitting matching strings.
	 */
	public void addNonMatcher(String delim) {
		if(currPatt == null) {
			currPatt          = new StringBuilder();
			currExclusionPatt = new StringBuilder();

			currExclusionPatt.append("(?:" + delim + ")");
		} else {
			currExclusionPatt.append("|(?:" + delim + ")");
		}
	}
	/**
	 * Compiles the current set of delimiters to a pattern.
	 *
	 * Makes this splitter ready to use.
	 */
	public void compile() {
		compPatt      = Pattern.compile(currPatt.toString());
		exclusionPatt = Pattern.compile(currExclusionPatt.toString());
	}
}