/*
 * Copyright Aduna (http://www.aduna-software.com/) (c) 2007.
 *
 * Licensed under the Aduna BSD-style license.
 */
package com.bigdata.rdf.sail.sparql;

import info.aduna.text.StringUtil;

/**
 * SPARQL-related utility methods.
 * 
 * @author Arjohn Kampman
 * @openrdf
 */
public class SPARQLUtil {

	/**
	 * Encodes the supplied string for inclusion as a 'normal' string in a SPARQL
	 * query.
	 */
	public static String encodeString(String s) {
		s = StringUtil.gsub("\\", "\\\\", s);
		s = StringUtil.gsub("\t", "\\t", s);
		s = StringUtil.gsub("\n", "\\n", s);
		s = StringUtil.gsub("\r", "\\r", s);
		s = StringUtil.gsub("\b", "\\b", s);
		s = StringUtil.gsub("\f", "\\f", s);
		s = StringUtil.gsub("\"", "\\\"", s);
		s = StringUtil.gsub("'", "\\'", s);
		return s;
	}

	/**
	 * Decodes an encoded SPARQL string. Any \-escape sequences are substituted
	 * with their decoded value.
	 * 
	 * @param s
	 *        An encoded SPARQL string.
	 * @return The unencoded string.
	 * @exception IllegalArgumentException
	 *            If the supplied string is not a correctly encoded SPARQL
	 *            string.
	 */
	public static String decodeString(String s) {
		int backSlashIdx = s.indexOf('\\');

		if (backSlashIdx == -1) {
			// No escaped characters found
			return s;
		}

		int startIdx = 0;
		int sLength = s.length();
		StringBuilder sb = new StringBuilder(sLength);

		while (backSlashIdx != -1) {
			sb.append(s.substring(startIdx, backSlashIdx));

			if (backSlashIdx + 1 >= sLength) {
				throw new IllegalArgumentException("Unescaped backslash in: " + s);
			}

			char c = s.charAt(backSlashIdx + 1);

			if (c == 't') {
				sb.append('\t');
				startIdx = backSlashIdx + 2;
			}
			else if (c == 'n') {
				sb.append('\n');
				startIdx = backSlashIdx + 2;
			}
			else if (c == 'r') {
				sb.append('\r');
				startIdx = backSlashIdx + 2;
			}
			else if (c == 'b') {
				sb.append('\b');
				startIdx = backSlashIdx + 2;
			}
			else if (c == 'f') {
				sb.append('\f');
				startIdx = backSlashIdx + 2;
			}
			else if (c == '"') {
				sb.append('"');
				startIdx = backSlashIdx + 2;
			}
			else if (c == '\'') {
				sb.append('\'');
				startIdx = backSlashIdx + 2;
			}
			else if (c == '\\') {
				sb.append('\\');
				startIdx = backSlashIdx + 2;
			}
			else {
				throw new IllegalArgumentException("Unescaped backslash in: " + s);
			}

			backSlashIdx = s.indexOf('\\', startIdx);
		}

		sb.append(s.substring(startIdx));

		return sb.toString();
	}
}