package org.expeditee.gui.management;

public class ResourceUtil {
	
	private static final char PATTERN_START_TWO = '{';
	private static final char PATTERN_START_ONE = '$';
	private static final char PATTERN_END = '}';
	private static final char ESCAPE = '\\';

	public static final String CURRENT_FRAMESET_FLAG = "${CURRENT_FRAMESET}";
	public static final String CURRENT_USER = "${CURRENT_USER}";
	
	/**
	 * Utility function that transforms a input string to a output string.
	 * Any occurances of 'pattern' are replaced with 'replacement'.
	 * \ is used as the escape key.
	 * @param input The raw input
	 * @param pattern The pattern to replace.  
	 * This will be prepended by in ${ and appended by } in the input string.
	 * @param replacement The replacement content to use.
	 * @return The transformed string.
	 */
	protected static String substitute(String input, String pattern, String replacement) {		
		StringBuilder outputSB = new StringBuilder();
		StringBuilder inputSB = new StringBuilder(input.replace("\\", "\\\\") + ResourceUtil.ESCAPE);
		StringBuilder patternSB = new StringBuilder();
		boolean inPattern = false;
		boolean patternStartPossible = true;
		
		int index = 0;
		int length = inputSB.length() - 1;
		while (index < length) {
			char c = inputSB.charAt(index);
			boolean startingPattern = patternStartPossible && 
					c == ResourceUtil.PATTERN_START_TWO &&
					outputSB.charAt(outputSB.length() - 1) == ResourceUtil.PATTERN_START_ONE;
			boolean endingPattern = c == ResourceUtil.PATTERN_END;
			
			if (c == ResourceUtil.ESCAPE && !inPattern) {
				index++;
				c = inputSB.charAt(index);
				outputSB.append(c);
				if (c == PATTERN_START_ONE) {
					patternStartPossible = false;
				}
			} else if (inPattern && endingPattern) {
				String patternFound = patternSB.toString();
				if (patternFound.equals(pattern)) {
					outputSB.append(replacement);
				} else {
					outputSB.append("" + ResourceUtil.PATTERN_START_ONE + ResourceUtil.PATTERN_START_TWO);
					outputSB.append(patternFound);
					outputSB.append(ResourceUtil.PATTERN_END);
				}
				inPattern = false;
				patternSB = new StringBuilder();
			} else if (!inPattern && startingPattern) {
				outputSB.deleteCharAt(outputSB.length() - 1);
				inPattern = true;
			} else if (inPattern) {
				patternSB.append(c);
			} else {
				outputSB.append(c);
				patternStartPossible = true;
			}
			
			index++;
		}
		
		if (patternSB.length() > 0) {
			outputSB.append("${");
		}
		outputSB.append(patternSB);
		return outputSB.toString();
	}
}