/*
    * Copyright (C) 2009 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.util.concurrent;
  
  import static com.google.common.base.Preconditions.checkNotNull;
  
  import com.google.common.base.Supplier;
  
  import java.util.concurrent.Callable;
  
  import javax.annotation.Nullable;
  
  /**
   * Static utility methods pertaining to the {@link Callable} interface.
   *
   * @author Isaac Shum
   * @since 1.0
   */
  public final class Callables {
    private Callables() {}
  
    /**
     * Creates a {@code Callable} which immediately returns a preset value each
     * time it is called.
     */
    public static <T> Callable<T> returning(final @Nullable T value) {
      return new Callable<T>() {
        @Override public T call() {
          return value;
        }
      };
    }
  
    /**
     * Wraps the given callable such that for the duration of {@link Callable#call} the thread that is
     * running will have the given name.
     *
     *
     * @param callable The callable to wrap
     * @param nameSupplier The supplier of thread names, {@link Supplier#get get} will be called once
     *     for each invocation of the wrapped callable.
     */
    static <T> Callable<T> threadRenaming(final Callable<T> callable,
        final Supplier<String> nameSupplier) {
      checkNotNull(nameSupplier);
      checkNotNull(callable);
      return new Callable<T>() {
        @Override public T call() throws Exception {
          Thread currentThread = Thread.currentThread();
          String oldName = currentThread.getName();
          boolean restoreName = trySetName(nameSupplier.get(), currentThread);
          try {
            return callable.call();
          } finally {
            if (restoreName) {
              trySetName(oldName, currentThread);
            }
          }
        }
      };
    }
  
    /**
     * Wraps the given runnable such that for the duration of {@link Runnable#run} the thread that is
     * running with have the given name.
     *
     *
     * @param task The Runnable to wrap
     * @param nameSupplier The supplier of thread names, {@link Supplier#get get} will be called once
     *     for each invocation of the wrapped callable.
     */
    static Runnable threadRenaming(final Runnable task, final Supplier<String> nameSupplier) {
      checkNotNull(nameSupplier);
      checkNotNull(task);
      return new Runnable() {
        @Override public void run() {
          Thread currentThread = Thread.currentThread();
          String oldName = currentThread.getName();
          boolean restoreName = trySetName(nameSupplier.get(), currentThread);
          try {
            task.run();
          } finally {
            if (restoreName) {
              trySetName(oldName, currentThread);
            }
         }
       }
     };
   }
 
   /** Tries to set name of the given {@link Thread}, returns true if successful. */
   private static boolean trySetName(final String threadName, Thread currentThread) {
     // In AppEngine this will always fail, should we test for that explicitly using
     // MoreExecutors.isAppEngine.  More generally, is there a way to see if we have the modifyThread
     // permission without catching an exception?
     try {
       currentThread.setName(threadName);
       return true;
     } catch (SecurityException e) {
       return false;
     }
   }
 }