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Query language parser implementation for SeRQL.
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/*******************************************************************************
 * Copyright (c) 2015 Eclipse RDF4J contributors, Aduna, and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Distribution License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *******************************************************************************/
package org.eclipse.rdf4j.query.parser.serql;

import org.eclipse.rdf4j.common.text.StringUtil;

/**
 * SeRQL-related utility methods.
 *
 * @author Arjohn Kampman
 */
public class SeRQLUtil {

	/**
	 * Encodes the supplied string for inclusion as a 'normal' string in a SeRQL 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);
		return s;
	}

	/**
	 * Decodes an encoded SeRQL string. Any \-escape sequences are substituted with their decoded value.
	 *
	 * @param s An encoded SeRQL string.
	 * @return The unencoded string.
	 * @exception IllegalArgumentException If the supplied string is not a correctly encoded SeRQL 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 == 'u') {
				// \\uxxxx
				if (backSlashIdx + 5 >= sLength) {
					throw new IllegalArgumentException("Incomplete Unicode escape sequence in: " + s);
				}
				String xx = s.substring(backSlashIdx + 2, backSlashIdx + 6);

				try {
					c = (char) Integer.parseInt(xx, 16);
					sb.append(c);

					startIdx = backSlashIdx + 6;
				} catch (NumberFormatException e) {
					throw new IllegalArgumentException("Illegal Unicode escape sequence '\\u" + xx + "' in: " + s);
				}
			} else if (c == 'U') {
				// \\Uxxxxxxxx
				if (backSlashIdx + 9 >= sLength) {
					throw new IllegalArgumentException("Incomplete Unicode escape sequence in: " + s);
				}
				String xx = s.substring(backSlashIdx + 2, backSlashIdx + 10);

				try {
					c = (char) Integer.parseInt(xx, 16);
					sb.append(c);

					startIdx = backSlashIdx + 10;
				} catch (NumberFormatException e) {
					throw new IllegalArgumentException("Illegal Unicode escape sequence '\\U" + xx + "' in: " + s);
				}
			} else {
				throw new IllegalArgumentException("Unescaped backslash in: " + s);
			}

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

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

		return sb.toString();
	}
}