Subject.java

/*
 *   Copyright (c) 2012 Mike Heath.  All rights reserved.
 *
 *   Licensed under the Apache License, Version 2.0 (the "License");
 *   you may not use this file except in compliance with the License.
 *   You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *   Unless required by applicable law or agreed to in writing, software
 *   distributed under the License is distributed on an "AS IS" BASIS,
 *   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *   See the License for the specific language governing permissions and
 *   limitations under the License.
 *
 */
package cloudeventbus;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.ThreadLocalRandom;
import java.util.regex.Pattern;

/**
 * Class for holding a subject. Facilitates validating a subject is a "sub" subject.
 *
 * @author Mike Heath <elcapo@gmail.com>
 */
public class Subject {

	public static final String WILD_CARD_TOKEN = "*";
	public static final Subject ALL = new Subject("*");
	private static final char[] VALID_SUBJECT_CHARS = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ".toCharArray();
	private static final Pattern SUBJECT_PATTERN = Pattern.compile("[0-9a-zA-Z_-]+(\\.[0-9a-zA-Z_-]+)*(\\.\\*){0,1}");

	public static List<Subject> list(String... subjects) {
		final Subject[] list = new Subject[subjects.length];
		for (int i = 0; i < subjects.length; i++) {
			list[i] = new Subject(subjects[i]);
		}
		return Collections.unmodifiableList(Arrays.asList(list));
	}

	public static List<Subject> list(List<String> subjects) {
		final List<Subject> list = new ArrayList<>(subjects.size());
		for (String subject : subjects) {
			list.add(new Subject(subject));
		}
		return Collections.unmodifiableList(list);
	}

	public static Subject createRequestReplySubject() {
		final ThreadLocalRandom random = ThreadLocalRandom.current();
		final char[] randomChars = new char[Constants.REQUEST_REPLY_SUBJECT_SIZE];
		for (int i=0; i < Constants.REQUEST_REPLY_SUBJECT_SIZE; i++) {
			randomChars[i] = VALID_SUBJECT_CHARS[random.nextInt(VALID_SUBJECT_CHARS.length)];
		}
		return new Subject(Constants.REQUEST_REPLY_SUBJECT_PREFIX + new String(randomChars));
	}

	public static boolean isRequestReplySubject(String subject) {
		return subject != null && subject.startsWith(Constants.REQUEST_REPLY_SUBJECT_PREFIX);
	}

	private final String subject;

	public Subject(String subject) {
		if (subject == null) {
			throw new NullPointerException("subject can not be null");
		}
		if (!WILD_CARD_TOKEN.equals(subject) && !SUBJECT_PATTERN.matcher(subject).matches()) {
			throw new IllegalArgumentException("Not valid subject syntax.");
		}
		this.subject = subject;
	}

	public boolean isWildCard() {
		return subject.endsWith(WILD_CARD_TOKEN);
	}

	public boolean isSub(Subject subSubject) {
		if (subject.equals(WILD_CARD_TOKEN)) {
			return true;
		}
		if (isWildCard()) {
			final String subjectSansWildcard = subject.substring(0, subject.length() - 1);
			return subSubject.subject.startsWith(subjectSansWildcard);
		}
		return equals(subSubject);
	}

	public boolean isRequestReply() {
		return isRequestReplySubject(subject);
	}

	@Override
	public int hashCode() {
		return subject.hashCode();
	}

	@Override
	public boolean equals(Object obj) {
		if (obj == null) { return false; }
		return obj.getClass() == Subject.class && subject.equals(((Subject) obj).subject);
	}

	/**
	 * Returns the subject as a string.
	 * @return the subject as a string.
	 */
	@Override
	public String toString() {
		return subject;
	}

}