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Basic utility library containing several useful classes (e.g., a Pair class) to ease everyday programming.
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/* Copyright (C) 2013 TU Dortmund
 * This file is part of AutomataLib, http://www.automatalib.net/.
 * 
 * AutomataLib is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License version 3.0 as published by the Free Software Foundation.
 * 
 * AutomataLib is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with AutomataLib; if not, see
 * http://www.gnu.de/documents/lgpl.en.html.
 */
package net.automatalib.commons.util.strings;

import java.io.IOException;
import java.util.regex.Pattern;

/**
 * Misceallanous utility functions for {@link String}s.
 * 
 * @author Malte Isberner 
 */
public abstract class StringUtil {
	
	private static final String IDENTIFIER_REGEX = "[a-zA-Z_]\\w*";
	
	private static Pattern identifierPattern = null;
	
	private StringUtil() {}
	

	public static Pattern getIdentifierPattern() {
		if(identifierPattern == null)
			identifierPattern = Pattern.compile(IDENTIFIER_REGEX);
		return identifierPattern;
	}
	
	public static String enquote(String s) {
		StringBuilder sb = new StringBuilder(s.length() + 2);
		try {
			enquote(s, sb);
		}
		catch(IOException e) {}
		return sb.toString();
	}
	
	public static void enquote(String s, Appendable a) throws IOException {
		a.append('"');
		escapeQuotes(s, a);
		a.append('"');
	}
	
	public static void enquoteIfNecessary(String s, Appendable a) throws IOException {
		if(!getIdentifierPattern().matcher(s).matches())
			enquote(s, a);
		else
			a.append(s);
	}
	
	public static void enquoteIfNecessary(String s, Appendable a, Pattern valid)
			throws IOException {
		if(!valid.matcher(s).matches())
			enquote(s, a);
		else
			a.append(s);
	}
	
	public static void enquoteIfNecessary(String s, Appendable a,
			Pattern valid,
			Pattern exception) throws IOException {
		if(!valid.matcher(s).matches() || exception.matcher(s).matches())
			enquote(s, a);
		else
			a.append(s);
	}
	
	public static String unquote(String s) {
		StringBuilder sb = new StringBuilder(s.length() - 2);
		try {
			unquote(s, sb);
		}
		catch(IOException e) {}
		return sb.toString();
	}
	
	public static void unquote(String s, Appendable a) throws IOException {
		if(s.charAt(0) != '"' || s.charAt(s.length()-1) != '"')
			throw new IllegalArgumentException("Argument to StringUtil.unquote() must begin and end with a double quote ('\"').");
		unescapeQuotes(s.substring(1, s.length()-1));
	}
	
	/**
	 * Unescapes escaped double quotes in a string, i.e.
	 * replaces \" by " and
	 * \\ by \.
	 * 
	 * @param s the string in which to unescape double quotes.
	 * @return the unescaped string.
	 */
	public static String unescapeQuotes(String s) {
		StringBuilder sb = new StringBuilder(s.length());
		try {
			unescapeQuotes(s, sb);
		}
		catch(IOException e) {}
		return sb.toString();
	}
	
	public static void unescapeQuotes(String s, Appendable a) throws IOException {
		int eos = s.length() - 1;
		for(int i = 0; i < eos; i++) {
			char c = s.charAt(i);
			if(c == '\\') {
				c = s.charAt(++i);
				if(c != '"' && c != '\\')
					a.append('\\');
			}
			a.append(c);
		}
		
		a.append(s.charAt(eos));
	}

	/**
	 * Escapes double quotes in a string. Effectively, " is
	 * replaced by \" and \ is replaced by
	 * \\.
	 * 
	 * @param s the string to escape.
	 * @return the escaped string.
	 */
	public static String escapeQuotes(String s) {
		StringBuilder sb = new StringBuilder(s.length());
		try {
			escapeQuotes(s, sb);
		}
		catch(IOException e) {}
		return sb.toString();
	}
	
	public static void escapeQuotes(String s, Appendable a) throws IOException {
		for(int i = 0; i < s.length(); i++) {
			char c = s.charAt(i);
			
			if(c == '\\' || c == '"')
				a.append('\\');
			a.append(c);
		}
	}
	
	
	public static void appendObject(Appendable a, Object obj) throws IOException {
		if(obj instanceof Printable)
			((Printable)obj).print(a);
		else
			a.append(String.valueOf(obj));
	}
	
	public static void appendArray(Appendable a, Object[] array, String sepString) throws IOException {
		boolean first = true;
		
		for(Object o : array) {
			if(first)
				first = false;
			else
				a.append(sepString);
			appendObject(a, o);
		}
	}
	
	public static void appendArrayEnquoted(Appendable a, Object[] array, String sepString) throws IOException {
		boolean first = true;
		
		for(Object o : array) {
			if(first)
				first = false;
			else
				a.append(sepString);
			enquote(String.valueOf(o), a);
		}
	}
	
	public static void appendIterable(Appendable a, Iterable it, String sepString) throws IOException {
		boolean first = true;
		
		for(Object o : it) {
			if(first)
				first = false;
			else
				a.append(sepString);
			appendObject(a, o);
		}
	}
	
	public static void appendIterableEnquoted(Appendable a, Iterable it, String sepString) throws IOException {
		boolean first = true;
		
		for(Object o : it) {
			if(first)
				first = false;
			else
				a.append(sepString);
			if(o == null)
				a.append("null");
			else
				enquote(o.toString(), a);
		}
	}
}