/*
 * Copyright (C) 2007 The Guava 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 com.google.common.base;

import static com.google.common.base.Preconditions.checkNotNull;
import static java.util.Arrays.asList;
import static java.util.Collections.unmodifiableList;

import com.google.common.annotations.Beta;
import com.google.common.annotations.VisibleForTesting;

import java.io.PrintWriter;
import java.io.StringWriter;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.AbstractList;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import javax.annotation.CheckReturnValue;
import javax.annotation.Nullable;

/**
 * Static utility methods pertaining to instances of {@link Throwable}.
 *
 * <p>See the Guava User Guide entry on <a href=
 * "https://github.com/google/guava/wiki/ThrowablesExplained">Throwables</a>.
 *
 * @author Kevin Bourrillion
 * @author Ben Yu
 * @since 1.0
 */
public final class Throwables {
  private Throwables() {}

  /**
   * Propagates {@code throwable} exactly as-is, if and only if it is an instance of {@code
   * declaredType}.  Example usage:
   * <pre>
   *   try {
   *     someMethodThatCouldThrowAnything();
   *   } catch (IKnowWhatToDoWithThisException e) {
   *     handle(e);
   *   } catch (Throwable t) {
   *     Throwables.propagateIfInstanceOf(t, IOException.class);
   *     Throwables.propagateIfInstanceOf(t, SQLException.class);
   *     throw Throwables.propagate(t);
   *   }
   * </pre>
   */
  public static <X extends Throwable> void propagateIfInstanceOf(
      @Nullable Throwable throwable, Class<X> declaredType) throws X {
    // Check for null is needed to avoid frequent JNI calls to isInstance().
    if (throwable != null && declaredType.isInstance(throwable)) {
      throw declaredType.cast(throwable);
    }
  }

  /**
   * Propagates {@code throwable} exactly as-is, if and only if it is an instance of {@link
   * RuntimeException} or {@link Error}.  Example usage:
   * <pre>
   *   try {
   *     someMethodThatCouldThrowAnything();
   *   } catch (IKnowWhatToDoWithThisException e) {
   *     handle(e);
   *   } catch (Throwable t) {
   *     Throwables.propagateIfPossible(t);
   *     throw new RuntimeException("unexpected", t);
   *   }
   * </pre>
   */
  public static void propagateIfPossible(@Nullable Throwable throwable) {
    propagateIfInstanceOf(throwable, Error.class);
    propagateIfInstanceOf(throwable, RuntimeException.class);
  }

  /**
   * Propagates {@code throwable} exactly as-is, if and only if it is an instance of {@link
   * RuntimeException}, {@link Error}, or {@code declaredType}. Example usage:
   * <pre>
   *   try {
   *     someMethodThatCouldThrowAnything();
   *   } catch (IKnowWhatToDoWithThisException e) {
   *     handle(e);
   *   } catch (Throwable t) {
   *     Throwables.propagateIfPossible(t, OtherException.class);
   *     throw new RuntimeException("unexpected", t);
   *   }
   * </pre>
   *
   * @param throwable the Throwable to possibly propagate
   * @param declaredType the single checked exception type declared by the calling method
   */
  public static <X extends Throwable> void propagateIfPossible(
      @Nullable Throwable throwable, Class<X> declaredType) throws X {
    propagateIfInstanceOf(throwable, declaredType);
    propagateIfPossible(throwable);
  }

  /**
   * Propagates {@code throwable} exactly as-is, if and only if it is an instance of {@link
   * RuntimeException}, {@link Error}, {@code declaredType1}, or {@code declaredType2}. In the
   * unlikely case that you have three or more declared checked exception types, you can handle them
   * all by invoking these methods repeatedly. See usage example in {@link
   * #propagateIfPossible(Throwable, Class)}.
   *
   * @param throwable the Throwable to possibly propagate
   * @param declaredType1 any checked exception type declared by the calling method
   * @param declaredType2 any other checked exception type declared by the calling method
   */
  public static <X1 extends Throwable, X2 extends Throwable> void propagateIfPossible(
      @Nullable Throwable throwable, Class<X1> declaredType1, Class<X2> declaredType2)
      throws X1, X2 {
    checkNotNull(declaredType2);
    propagateIfInstanceOf(throwable, declaredType1);
    propagateIfPossible(throwable, declaredType2);
  }

  /**
   * Propagates {@code throwable} as-is if it is an instance of {@link RuntimeException} or {@link
   * Error}, or else as a last resort, wraps it in a {@code RuntimeException} and then propagates.
   * <p>
   * This method always throws an exception. The {@code RuntimeException} return type is only for
   * client code to make Java type system happy in case a return value is required by the enclosing
   * method. Example usage:
   * <pre>
   *   T doSomething() {
   *     try {
   *       return someMethodThatCouldThrowAnything();
   *     } catch (IKnowWhatToDoWithThisException e) {
   *       return handle(e);
   *     } catch (Throwable t) {
   *       throw Throwables.propagate(t);
   *     }
   *   }
   * </pre>
   *
   * @param throwable the Throwable to propagate
   * @return nothing will ever be returned; this return type is only for your convenience, as
   *     illustrated in the example above
   */
  public static RuntimeException propagate(Throwable throwable) {
    propagateIfPossible(checkNotNull(throwable));
    throw new RuntimeException(throwable);
  }

  /**
   * Returns the innermost cause of {@code throwable}. The first throwable in a
   * chain provides context from when the error or exception was initially
   * detected. Example usage:
   * <pre>
   *   assertEquals("Unable to assign a customer id", Throwables.getRootCause(e).getMessage());
   * </pre>
   */
  @CheckReturnValue
  public static Throwable getRootCause(Throwable throwable) {
    Throwable cause;
    while ((cause = throwable.getCause()) != null) {
      throwable = cause;
    }
    return throwable;
  }

  /**
   * Gets a {@code Throwable} cause chain as a list.  The first entry in the list will be {@code
   * throwable} followed by its cause hierarchy.  Note that this is a snapshot of the cause chain
   * and will not reflect any subsequent changes to the cause chain.
   *
   * <p>Here's an example of how it can be used to find specific types of exceptions in the cause
   * chain:
   *
   * <pre>
   * Iterables.filter(Throwables.getCausalChain(e), IOException.class));
   * </pre>
   *
   * @param throwable the non-null {@code Throwable} to extract causes from
   * @return an unmodifiable list containing the cause chain starting with {@code throwable}
   */
  @Beta // TODO(kevinb): decide best return type
  @CheckReturnValue
  public static List<Throwable> getCausalChain(Throwable throwable) {
    checkNotNull(throwable);
    List<Throwable> causes = new ArrayList<Throwable>(4);
    while (throwable != null) {
      causes.add(throwable);
      throwable = throwable.getCause();
    }
    return Collections.unmodifiableList(causes);
  }

  /**
   * Returns a string containing the result of {@link Throwable#toString() toString()}, followed by
   * the full, recursive stack trace of {@code throwable}. Note that you probably should not be
   * parsing the resulting string; if you need programmatic access to the stack frames, you can call
   * {@link Throwable#getStackTrace()}.
   */
  @CheckReturnValue
  public static String getStackTraceAsString(Throwable throwable) {
    StringWriter stringWriter = new StringWriter();
    throwable.printStackTrace(new PrintWriter(stringWriter));
    return stringWriter.toString();
  }

  /**
   * Returns the stack trace of {@code throwable}, possibly providing slower iteration over the full
   * trace but faster iteration over parts of the trace. Here, "slower" and "faster" are defined in
   * comparison to the normal way to access the stack trace, {@link Throwable#getStackTrace()
   * throwable.getStackTrace()}. Note, however, that this method's special implementation is not
   * available for all platforms and configurations. If that implementation is unavailable, this
   * method falls back to {@code getStackTrace}. Callers that require the special implementation can
   * check its availability with {@link #lazyStackTraceIsLazy()}.
   *
   * <p>The expected (but not guaranteed) performance of the special implementation differs from
   * {@code getStackTrace} in one main way: The {@code lazyStackTrace} call itself returns quickly
   * by delaying the per-stack-frame work until each element is accessed. Roughly speaking:
   *
   * <ul>
   * <li>{@code getStackTrace} takes {@code stackSize} time to return but then negligible time to
   * retrieve each element of the returned list.
   * <li>{@code lazyStackTrace} takes negligible time to return but then {@code 1/stackSize} time to
   * retrieve each element of the returned list (probably slightly more than {@code 1/stackSize}).
   * </ul>
   *
   * <p>Note: The special implementation does not respect calls to {@link Throwable#setStackTrace
   * throwable.setStackTrace}. Instead, it always reflects the original stack trace from the
   * exception's creation.
   *
   * @since 19.0
   */
  // TODO(cpovirk): Say something about the possibility that List access could fail at runtime?
  @Beta
  @CheckReturnValue
  public static List<StackTraceElement> lazyStackTrace(Throwable throwable) {
    return lazyStackTraceIsLazy()
        ? jlaStackTrace(throwable)
        : unmodifiableList(asList(throwable.getStackTrace()));
  }

  /**
   * Returns whether {@link #lazyStackTrace} will use the special implementation described in its
   * documentation.
   *
   * @since 19.0
   */
  @Beta
  @CheckReturnValue
  public static boolean lazyStackTraceIsLazy() {
    return getStackTraceElementMethod != null & getStackTraceDepthMethod != null;
  }

  private static List<StackTraceElement> jlaStackTrace(final Throwable t) {
    checkNotNull(t);
    /*
     * TODO(cpovirk): Consider optimizing iterator() to catch IOOBE instead of doing bounds checks.
     *
     * TODO(cpovirk): Consider the UnsignedBytes pattern if it performs faster and doesn't cause
     * AOSP grief.
     */
    return new AbstractList<StackTraceElement>() {
      @Override
      public StackTraceElement get(int n) {
        return (StackTraceElement)
            invokeAccessibleNonThrowingMethod(getStackTraceElementMethod, jla, t, n);
      }

      @Override
      public int size() {
        return (Integer) invokeAccessibleNonThrowingMethod(getStackTraceDepthMethod, jla, t);
      }
    };
  }

  private static Object invokeAccessibleNonThrowingMethod(
      Method method, Object receiver, Object... params) {
    try {
      return method.invoke(receiver, params);
    } catch (IllegalAccessException e) {
      throw new RuntimeException(e);
    } catch (InvocationTargetException e) {
      throw propagate(e.getCause());
    }
  }

  /** JavaLangAccess class name to load using reflection */
  private static final String JAVA_LANG_ACCESS_CLASSNAME = "sun.misc.JavaLangAccess";

  /** SharedSecrets class name to load using reflection */
  @VisibleForTesting static final String SHARED_SECRETS_CLASSNAME = "sun.misc.SharedSecrets";

  /** Access to some fancy internal JVM internals. */
  @Nullable private static final Object jla = getJLA();

  /**
   * The "getStackTraceElementMethod" method, only available on some JDKs so we use reflection to
   * find it when available. When this is null, use the slow way.
   */
  @Nullable
  private static final Method getStackTraceElementMethod = (jla == null) ? null : getGetMethod();

  /**
   * The "getStackTraceDepth" method, only available on some JDKs so we use reflection to find it
   * when available. When this is null, use the slow way.
   */
  @Nullable
  private static final Method getStackTraceDepthMethod = (jla == null) ? null : getSizeMethod();

  /**
   * Returns the JavaLangAccess class that is present in all Sun JDKs. It is not whitelisted for
   * AppEngine, and not present in non-Sun JDKs.
   */
  @Nullable
  private static Object getJLA() {
    try {
      /*
       * We load sun.misc.* classes using reflection since Android doesn't support these classes and
       * would result in compilation failure if we directly refer to these classes.
       */
      Class<?> sharedSecrets = Class.forName(SHARED_SECRETS_CLASSNAME, false, null);
      Method langAccess = sharedSecrets.getMethod("getJavaLangAccess");
      return langAccess.invoke(null);
    } catch (ThreadDeath death) {
      throw death;
    } catch (Throwable t) {
      /*
       * This is not one of AppEngine's whitelisted classes, so even in Sun JDKs, this can fail with
       * a NoClassDefFoundError. Other apps might deny access to sun.misc packages.
       */
      return null;
    }
  }

  /**
   * Returns the Method that can be used to resolve an individual StackTraceElement, or null if that
   * method cannot be found (it is only to be found in fairly recent JDKs).
   */
  @Nullable
  private static Method getGetMethod() {
    return getJlaMethod("getStackTraceElement", Throwable.class, int.class);
  }

  /**
   * Returns the Method that can be used to return the size of a stack, or null if that method
   * cannot be found (it is only to be found in fairly recent JDKs).
   */
  @Nullable
  private static Method getSizeMethod() {
    return getJlaMethod("getStackTraceDepth", Throwable.class);
  }

  @Nullable
  private static Method getJlaMethod(String name, Class<?>... parameterTypes) throws ThreadDeath {
    try {
      return Class.forName(JAVA_LANG_ACCESS_CLASSNAME, false, null).getMethod(name, parameterTypes);
    } catch (ThreadDeath death) {
      throw death;
    } catch (Throwable t) {
      /*
       * Either the JavaLangAccess class itself is not found, or the method is not supported on the
       * JVM.
       */
      return null;
    }
  }
}