RegExTransformationService.java

/**
 * Copyright (c) 2014-2017 by the respective copyright holders.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 */
package org.eclipse.smarthome.transform.regex.internal;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

import org.eclipse.smarthome.core.transform.TransformationException;
import org.eclipse.smarthome.core.transform.TransformationService;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * <p>
 * The implementation of {@link TransformationService} which transforms the input by Regular Expressions.
 * </p>
 * <p>
 * <b>Note:</b> the given Regular Expression must contain exactly one group!
 *
 * @author Thomas.Eichstaedt-Engelen
 */
public class RegExTransformationService implements TransformationService {

    private final Logger logger = LoggerFactory.getLogger(RegExTransformationService.class);

    private static final Pattern substPattern = Pattern.compile("^s/(.*?[^\\\\])/(.*?[^\\\\])/(.*)$");

    /**
     * @{inheritDoc
     */
    @Override
    public String transform(String regExpression, String source) throws TransformationException {

        if (regExpression == null || source == null) {
            throw new TransformationException("the given parameters 'regex' and 'source' must not be null");
        }

        logger.debug("about to transform '{}' by the function '{}'", source, regExpression);

        String result = "";

        Matcher substMatcher = substPattern.matcher(regExpression);
        if (substMatcher.matches()) {
            logger.debug("Using substitution form of regex transformation");
            String regex = substMatcher.group(1);
            String substitution = substMatcher.group(2);
            String options = substMatcher.group(3);
            if (options.equals("g")) {
                result = source.trim().replaceAll(regex, substitution);
            } else {
                result = source.trim().replaceFirst(regex, substitution);
            }
            if (result != null) {
                return result;
            }
        }

        Matcher matcher = Pattern.compile("^" + regExpression + "$", Pattern.DOTALL).matcher(source.trim());
        if (!matcher.matches()) {
            logger.debug(
                    "the given regex '^{}$' doesn't match the given content '{}' -> couldn't compute transformation",
                    regExpression, source);
            return null;
        }
        matcher.reset();

        while (matcher.find()) {

            if (matcher.groupCount() == 0) {
                logger.info(
                        "the given regular expression '^{}$' doesn't contain a group. No content will be extracted and returned!",
                        regExpression);
                continue;
            }

            result = matcher.group(1);

            if (matcher.groupCount() > 1) {
                logger.debug(
                        "the given regular expression '^{}$' contains more than one group. Only the first group will be returned!",
                        regExpression);
            }
        }

        return result;
    }

}