/*
 * Copyright 2002-2021 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
 *
 *      https://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.test.util;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

/**
 * {@code ExceptionCollector} is a test utility for executing code blocks,
 * collecting exceptions, and generating a single {@link AssertionError}
 * containing any exceptions encountered as {@linkplain Throwable#getSuppressed()
 * suppressed exceptions}.
 *
 * <p>This utility is intended to support <em>soft assertion</em> use cases
 * similar to the {@code SoftAssertions} support in AssertJ and the
 * {@code assertAll()} support in JUnit Jupiter.
 *
 * @author Sam Brannen
 * @since 5.3.10
 */
public class ExceptionCollector {

	private final List<Throwable> exceptions = new ArrayList<>();


	/**
	 * Execute the supplied {@link Executable} and track any exception thrown.
	 * @param executable the {@code Executable} to execute
	 * @see #getExceptions()
	 * @see #assertEmpty()
	 */
	public void execute(Executable executable) {
		try {
			executable.execute();
		}
		catch (Throwable ex) {
			this.exceptions.add(ex);
		}
	}

	/**
	 * Get the list of exceptions encountered in {@link #execute(Executable)}.
	 * @return an unmodifiable copy of the list of exceptions, potentially empty
	 * @see #assertEmpty()
	 */
	public List<Throwable> getExceptions() {
		return Collections.unmodifiableList(this.exceptions);
	}

	/**
	 * Assert that this {@code ExceptionCollector} does not contain any
	 * {@linkplain #getExceptions() exceptions}.
	 * <p>If this collector is empty, this method is effectively a no-op.
	 * <p>If this collector contains a single {@link Error} or {@link Exception},
	 * this method rethrows the error or exception.
	 * <p>If this collector contains a single {@link Throwable}, this method throws
	 * an {@link AssertionError} with the error message of the {@code Throwable}
	 * and with the {@code Throwable} as the {@linkplain Throwable#getCause() cause}.
	 * <p>If this collector contains multiple exceptions, this method throws an
	 * {@code AssertionError} whose message is "Multiple Exceptions (#):"
	 * followed by a new line with the error message of each exception separated
	 * by a new line, with {@code #} replaced with the number of exceptions present.
	 * In addition, each exception will be added to the {@code AssertionError} as
	 * a {@link Throwable#addSuppressed(Throwable) suppressed exception}.
	 * @see #execute(Executable)
	 * @see #getExceptions()
	 */
	public void assertEmpty() throws Exception {
		if (this.exceptions.isEmpty()) {
			return;
		}

		if (this.exceptions.size() == 1) {
			Throwable exception = this.exceptions.get(0);
			if (exception instanceof Error) {
				throw (Error) exception;
			}
			if (exception instanceof Exception) {
				throw (Exception) exception;
			}
			AssertionError assertionError = new AssertionError(exception.getMessage());
			assertionError.initCause(exception);
			throw assertionError;
		}

		StringBuilder message = new StringBuilder();
		message.append("Multiple Exceptions (").append(this.exceptions.size()).append("):");
		for (Throwable exception : this.exceptions) {
			message.append('\n');
			message.append(exception.getMessage());
		}
		AssertionError assertionError = new AssertionError(message);
		this.exceptions.forEach(assertionError::addSuppressed);
		throw assertionError;
	}


	/**
	 * {@code Executable} is a functional interface that can be used to implement
	 * any generic block of code that potentially throws a {@link Throwable}.
	 *
	 * <p>The {@code Executable} interface is similar to {@link java.lang.Runnable},
	 * except that an {@code Executable} can throw any kind of exception.
	 */
	@FunctionalInterface
	public interface Executable {

		void execute() throws Throwable;

	}

}
