/*******************************************************************************
 * Copyright (c) 2009 Red Hat Inc. and others.
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 * 
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     Alexander Kurtakov - initial API and implementation
 *******************************************************************************/
package org.eclipse.dltk.sh.internal.ui.text;

import org.eclipse.jface.text.rules.ICharacterScanner;
import org.eclipse.jface.text.rules.IRule;
import org.eclipse.jface.text.rules.IToken;
import org.eclipse.jface.text.rules.IWordDetector;
import org.eclipse.jface.text.rules.Token;

/**
 * This rule captures parameter expansions that are not covered by
 * DollarBraceCountingRule. That is, all dollar-prefixed variables including
 * special variables where encapsulation in braces is not necessary.
 */
public class DollarRule implements IRule {

	private final StringBuffer buffer = new StringBuffer();
	private final IToken defaultToken;
	private final IWordDetector detector;
	private final IToken successToken;

	public DollarRule(IWordDetector detector, IToken defaultToken, IToken token) {
		this.detector = detector;
		this.successToken = token;
		this.defaultToken = defaultToken;
	}

	/**
	 * Returns whether the specified character is a special parameter in shell
	 * script. A dollar sign combined with any of the following characters will
	 * be highlighted, but no characters after that.
	 * <p>
	 * '*', '@' - positional parameters starting from 1<br>
	 * '#' - number of positional parameters<br>
	 * '?' - exit status of the last executed foreground command<br>
	 * '-' - current option flags<br>
	 * '$' - PID of the shell<br>
	 * '!' - PID of the last executed background command<br>
	 * '_' - pathname used to invoke the shell and every subsequent command <br>
	 * '0' - usually the name of the file used to invoke the shell<br>
	 * '1' to '9' - expands to the corresponding positional parameters,
	 * parameters 10+ must be referenced with braces like ${12}
	 *
	 * @param c
	 *            a character to test
	 * @return true if the specified character is a special parameter
	 */
	private static boolean isSpecial(char c) {
		return ((c == '*') || (c == '@') || (c == '#') || (c == '?') || (c == '-') || (c == '$') || (c == '!')
				|| (c == '_') || Character.isDigit(c));
	}

	@Override
	public IToken evaluate(ICharacterScanner scanner) {
		int c = scanner.read();
		if (detector.isWordStart((char) c)) {
			buffer.setLength(0);
			do {
				buffer.append((char) c);
				c = scanner.read();
				if ((buffer.length() == 1) && isSpecial((char) c)) {
					return successToken;
				}
			} while ((c != ICharacterScanner.EOF) && detector.isWordPart((char) c));
			scanner.unread();
			if (buffer.length() > 1) {
				return successToken;
			}
			if (defaultToken.isUndefined()) {
				unreadBuffer(scanner);
			}
			return defaultToken;
		}
		scanner.unread();
		return Token.UNDEFINED;
	}

	/**
	 * Returns the characters in the buffer to the scanner.
	 *
	 * @param scanner
	 *            the scanner to be used
	 */
	protected void unreadBuffer(ICharacterScanner scanner) {
		for (int i = buffer.length() - 1; i >= 0; i--) {
			scanner.unread();
		}
	}
}