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Provides common utility functions
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/*
 * Copyright (c) CQSE GmbH
 *
 * 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.conqat.lib.commons.error;

import java.util.ArrayList;
import java.util.List;
import java.util.Optional;

import org.checkerframework.checker.nullness.qual.NonNull;
import org.conqat.lib.commons.assertion.CCSMAssert;
import org.conqat.lib.commons.function.RunnableWithException;
import org.conqat.lib.commons.string.StringUtils;

/**
 * Utility functionality for exception handling.
 */
public class ExceptionUtils {

	/**
	 * Trims the given {@link StackOverflowError}'s stacktrace by omitting all redundant stack trace
	 * elements.
	 */
	public static void trimStackOverFlowTrace(StackOverflowError e) {
		List trimmedStackTrace = new ArrayList<>();
		StackTraceElement previousElement = null;
		StackTraceElement[] stackTrace = e.getStackTrace();
		for (int i = 0; i < stackTrace.length; i++) {
			StackTraceElement currentElement = stackTrace[i];
			if (!currentElement.equals(previousElement)) {
				trimmedStackTrace.add(stackTrace[i]);
				previousElement = currentElement;
			}
		}
		e.setStackTrace(trimmedStackTrace.toArray(new StackTraceElement[trimmedStackTrace.size()]));
	}

	/**
	 * Obtains the stack trace of the given {@link Throwable} as a string.
	 */
	public static String getStacktraceAsString(Throwable t) {
		return StringUtils.obtainStackTrace(t);
	}

	/**
	 * Adds the {@code suppressed} as {@link Throwable#addSuppressed(Throwable) suppressed} to the
	 * {@code suppressing} Throwable.
	 * 
	 * @return The {@code suppressing} Throwable.
	 */
	public static  T withSuppressed(@NonNull T suppressing, @NonNull Throwable suppressed) {
		suppressing.addSuppressed(suppressed);
		return suppressing;
	}

	/**
	 * Returns the first non-null message in the cause hierarchy of the given {@link Throwable}. Will
	 * return {@link Optional#empty()} if none is found.
	 */
	public static Optional getFirstNonNullCauseMessage(Throwable e) {
		if (e.getMessage() != null) {
			return Optional.of(e.getMessage());
		}

		Throwable currentStack = e;
		while (currentStack.getCause() != null) {
			currentStack = currentStack.getCause();
			if (currentStack.getMessage() != null) {
				return Optional.of(currentStack.getMessage());
			}
		}
		return Optional.empty();
	}

	/**
	 * Runs all the {@code runnables} even in case of exceptions. Any thrown exceptions are collected
	 * and added as suppressed exceptions to the first thrown exception, which is then re-thrown.
	 */
	@SafeVarargs
	public static  void runAllAndAddAsSuppressed(Class exceptionClass,
			RunnableWithException... runnables) throws E {
		ExceptionHolder holder = null;
		for (RunnableWithException runnable : runnables) {
			try {
				runnable.run();
			} catch (Exception e) {
				// Should either be of type E or RuntimeException
				if (holder != null) {
					holder.addSuppressed(e);
				} else {
					holder = new ExceptionHolder<>(exceptionClass, e);
				}
			}
		}
		if (holder != null) {
			holder.rethrow();
		}
	}

	private static final class ExceptionHolder {

		private final Exception exception;

		private ExceptionHolder(Class exceptionType, Exception exception) {
			CCSMAssert.isNotNull(exceptionType, () -> String.format("Expected \"%s\" to be not null", "exceptionType"));
			CCSMAssert.isNotNull(exception, () -> String.format("Expected \"%s\" to be not null", "exception"));
			if (!(exception instanceof RuntimeException || exceptionType.isInstance(exception))) {
				throw new AssertionError("The Expected exception was not of type RuntimeException or " + exceptionType,
						exception);
			}
			this.exception = exception;
		}

		/**
		 * Appends the specified {@code suppressed} to the exceptions that were suppressed in order to
		 * deliver the underlying exception.
		 * 
		 * @see Throwable#addSuppressed(Throwable)
		 */
		private void addSuppressed(Throwable suppressed) {
			if (suppressed != exception) {
				exception.addSuppressed(suppressed);
			}
		}

		/**
		 * @throws E
		 *             The original exception
		 */
		@SuppressWarnings("unchecked") // Type was verified during construction
		private void rethrow() throws E {
			// During runtime the cast will have no effect due to type-erasure,
			// so this will also work if "exception" is actually a RuntimeException and not
			// of type E
			throw (E) exception;
		}
	}
}