/*
 * Copyright 2012-2015 the original author or authors.
 *
 * 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 org.springframework.boot.developertools.restart;

import java.net.URL;
import java.net.URLClassLoader;
import java.util.Collections;
import java.util.LinkedHashSet;
import java.util.Set;

/**
 * Default {@link RestartInitializer} that only enable initial restart when running a
 * standard "main" method. Skips initialization when running "fat" jars (included
 * exploded) or when running from a test.
 *
 * @author Phillip Webb
 * @since 1.3.0
 */
public class DefaultRestartInitializer implements RestartInitializer {

	private static final Set<String> SKIPPED_STACK_ELEMENTS;
	static {
		Set<String> skipped = new LinkedHashSet<String>();
		skipped.add("org.junit.runners.");
		skipped.add("org.springframework.boot.test.");
		SKIPPED_STACK_ELEMENTS = Collections.unmodifiableSet(skipped);
	}

	@Override
	public URL[] getInitialUrls(Thread thread) {
		if (!isMain(thread)) {
			return null;
		}
		for (StackTraceElement element : thread.getStackTrace()) {
			if (isSkippedStackElement(element)) {
				return null;
			}
		}
		return getUrls(thread);
	}

	/**
	 * Returns if the thread is for a main invocation. By default checks the name of the
	 * thread and the context classloader.
	 * @param thread the thread to check
	 * @return {@code true} if the thread is a main invocation
	 */
	protected boolean isMain(Thread thread) {
		return thread.getName().equals("main")
				&& thread.getContextClassLoader().getClass().getName()
						.contains("AppClassLoader");
	}

	/**
	 * Checks if a specific {@link StackTraceElement} should cause the initializer to be
	 * skipped.
	 * @param element the stack element to check
	 * @return {@code true} if the stack element means that the initializer should be
	 * skipped
	 */
	protected boolean isSkippedStackElement(StackTraceElement element) {
		for (String skipped : SKIPPED_STACK_ELEMENTS) {
			if (element.getClassName().startsWith(skipped)) {
				return true;
			}
		}
		return false;
	}

	/**
	 * Return the URLs that should be used with initialization.
	 * @param thread the source thread
	 * @return the URLs
	 */
	protected URL[] getUrls(Thread thread) {
		return ChangeableUrls.fromUrlClassLoader(
				(URLClassLoader) thread.getContextClassLoader()).toArray();
	}

}
