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// *  http://www.apache.org/licenses/LICENSE-2.0                                                                             *
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package org.apache.juneau.common.internal;

import java.io.*;

import org.apache.juneau.common.utils.*;

/**
 * Various utility methods for creating and working with throwables.
 */
public class ThrowableUtils {

	/**
	 * Creates a new {@link RuntimeException}.
	 *
	 * @param cause The caused-by exception.
	 * @return A new {@link RuntimeException}, or the same exception if it's already of that type.
	 */
	public static RuntimeException asRuntimeException(Throwable cause) {
		return cast(RuntimeException.class, cause);
	}

	/**
	 * Casts or wraps the specified throwable to the specified type.
	 *
	 * @param  The class to cast to.
	 * @param type The class to cast to.
	 * @param t The throwable to cast.
	 * @return Either the same exception if it's already the specified type, or a wrapped exception.
	 */
	public static  T cast(Class type, Throwable t) {
		try {
			return type.isInstance(t) ? type.cast(t) : type.getConstructor(Throwable.class).newInstance(t);
		} catch (Exception e) {
			throw new IllegalArgumentException(e);
		}
	}

	/**
	 * Same as {@link Throwable#getCause()} but searches the throwable chain for an exception of the specified type.
	 *
	 * @param c The throwable type to search for.
	 * @param  The throwable type to search for.
	 * @param t The throwable to search.
	 * @return The exception, or null if not found.
	 */
	public static  T getCause(Class c, Throwable t) {
		while (t != null) {
			t = t.getCause();
			if (c.isInstance(t))
				return c.cast(t);
		}
		return null;
	}

	/**
	 * Allows you to wrap a supplier that throws an exception so that it can be used in a fluent interface.
	 *
	 * @param  The supplier type.
	 * @param supplier The supplier throwing an exception.
	 * @return The supplied result.
	 * @throws RuntimeException if supplier threw an exception.
	 */
	public static  T safeSupplier(SupplierWithThrowable supplier) {
		try {
			return supplier.get();
		} catch (RuntimeException t) {
			throw t;
		} catch (Throwable t) {
			throw asRuntimeException(t);
		}
	}

	/**
	 * Interface used with {@link #safeSupplier(SupplierWithThrowable)}.
	 */
	@SuppressWarnings("javadoc")
	@FunctionalInterface
	public interface SupplierWithThrowable {
		T get() throws Throwable;
	}

	/**
	 * Runs a snippet of code and encapsulates any throwable inside a {@link RuntimeException}.
	 *
	 * @param snippet The snippet of code to run.
	 */
	public static void safeRun(Snippet snippet) {
		try {
			snippet.run();
		} catch (RuntimeException t) {
			throw t;
		} catch (Throwable t) {
			throw asRuntimeException(t);
		}
	}

	/**
	 * Convenience method for getting a stack trace as a string.
	 *
	 * @param t The throwable to get the stack trace from.
	 * @return The same content that would normally be rendered via t.printStackTrace()
	 */
	public static String getStackTrace(Throwable t) {
		StringWriter sw = new StringWriter();
		try (PrintWriter pw = new PrintWriter(sw)) {
			t.printStackTrace(pw);
		}
		return sw.toString();
	}

	/**
	 * Calculates a 16-bit hash for the specified throwable based on it's stack trace.
	 *
	 * @param t The throwable to calculate the stack trace on.
	 * @param stopClass Optional stop class on which to stop calculation of a stack trace beyond when found.
	 * @return A calculated hash.
	 */
	public static int hash(Throwable t, String stopClass) {
		int i = 0;
		while (t != null) {
			for (StackTraceElement e : t.getStackTrace()) {
				if (e.getClassName().equals(stopClass))
					break;
				if (e.getClassName().indexOf('$') == -1)
					i ^= e.hashCode();
			}
			t = t.getCause();
		}
		return i;
	}
}