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

public class RxReplace {

    public static String text(String subjectString, Pattern regex, Function<String, String> fn) {
        StringBuffer resultString = new StringBuffer();
        Matcher regexMatcher = regex.matcher(subjectString);

        while (regexMatcher.find()) {
            regexMatcher.appendReplacement(resultString, fn.apply(subjectString.substring(regexMatcher.start(), regexMatcher.end())));
        }

        regexMatcher.appendTail(resultString);

        return resultString.toString();
    }

    public static String group(String subjectString, Pattern regex, Function<String, String> fn) {
        StringBuffer resultString = new StringBuffer();
        Matcher regexMatcher = regex.matcher(subjectString);

        while (regexMatcher.find()) {
            regexMatcher.appendReplacement(resultString, fn.apply(regexMatcher.group(1)));
        }

        regexMatcher.appendTail(resultString);

        return resultString.toString();
    }
}