package com.notsocomplex.regex;

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

import org.junit.Assert;
import org.junit.Test;

public class RegexReplaceGroupTest {


	@Test
	public void testReplacementWithGroupsMultipleMatches() {

		String text =
			"this sentence should start with a capital letter. this one also! "
			+ "what about this one? Or this one?";

		// Group 1: ([a-z])
		//			-Match a character, create a group (1)
		// Group 2: (.+?[.!?])
		//			-Match anything one or more time
		//			-Make the match non-greedy, so stop the match when minimum is reached
		//			-Followed by one of these character .!?. Could have used \p{Punct} also.
		String regex = "([a-z])(.+?[.!?])";

		// Enable case-insensitive in Java is done using flags from Pattern.
		// Without this flag, we would have needed [a-zA-z] in our first group.
		Pattern pattern = Pattern.compile(regex, Pattern.CASE_INSENSITIVE);
		Matcher matcher = pattern.matcher(text);

		StringBuffer sb = new StringBuffer();

		// For each match. There will be 4, one for each sentence
		while (matcher.find()) {

			// Get the first group, which is the first letter of the sentence. Matched by the ([a-z]).
			String firstLetter = matcher.group(1);

			// Replace the match from the beginning with the upper case value
			// of the first letter and the group with at position 2
			matcher.appendReplacement(sb, firstLetter.toUpperCase() + "$2");

		}

		// Append the tail, there should be none but it is always safer to
		// do this
		matcher.appendTail(sb);
		Assert.assertEquals(sb.toString(), "This sentence should start with a capital letter. This one also! What about this one? Or this one?");

	}

}