/*
    * 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 com.google.common.annotations.Beta;
  import com.google.common.base.Supplier;
  import com.google.common.base.Throwables;
  
  import java.util.concurrent.Executor;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.TimeoutException;
  import java.util.logging.Level;
  import java.util.logging.Logger;
  
  /**
   * Base class for services that can implement {@link #startUp}, {@link #run} and
   * {@link #shutDown} methods. This class uses a single thread to execute the
   * service; consider {@link AbstractService} if you would like to manage any
   * threading manually.
   *
   * @author Jesse Wilson
   * @since 1.0
   */
  @Beta
  public abstract class AbstractExecutionThreadService implements Service {
    private static final Logger logger = Logger.getLogger(
        AbstractExecutionThreadService.class.getName());
    
    /* use AbstractService for state management */
    private final Service delegate = new AbstractService() {
      @Override protected final void doStart() {
        Executor executor = MoreExecutors.renamingDecorator(executor(), new Supplier<String>() {
          @Override public String get() {
            return serviceName();
          }
        });
        executor.execute(new Runnable() {
          @Override
          public void run() {
            try {
              startUp();
              notifyStarted();
  
              if (isRunning()) {
                try {
                  AbstractExecutionThreadService.this.run();
                } catch (Throwable t) {
                  try {
                    shutDown();
                  } catch (Exception ignored) {
                    logger.log(Level.WARNING, 
                        "Error while attempting to shut down the service"
                        + " after failure.", ignored);
                  }
                  throw t;
                }
              }
  
              shutDown();
              notifyStopped();
            } catch (Throwable t) {
              notifyFailed(t);
              throw Throwables.propagate(t);
            }
          }
        });
      }
  
      @Override protected void doStop() {
        triggerShutdown();
      }
    };
  
    /**
     * Constructor for use by subclasses.
     */
    protected AbstractExecutionThreadService() {}
  
    /**
     * Start the service. This method is invoked on the execution thread.
     * 
     * <p>By default this method does nothing.
     */
    protected void startUp() throws Exception {}
  
   /**
    * Run the service. This method is invoked on the execution thread.
    * Implementations must respond to stop requests. You could poll for lifecycle
    * changes in a work loop:
    * <pre>
    *   public void run() {
    *     while ({@link #isRunning()}) {
    *       // perform a unit of work
    *     }
    *   }
    * </pre>
    * ...or you could respond to stop requests by implementing {@link
    * #triggerShutdown()}, which should cause {@link #run()} to return.
    */
   protected abstract void run() throws Exception;
 
   /**
    * Stop the service. This method is invoked on the execution thread.
    * 
    * <p>By default this method does nothing.
    */
   // TODO: consider supporting a TearDownTestCase-like API
   protected void shutDown() throws Exception {}
 
   /**
    * Invoked to request the service to stop.
    * 
    * <p>By default this method does nothing.
    */
   protected void triggerShutdown() {}
 
   /**
    * Returns the {@link Executor} that will be used to run this service.
    * Subclasses may override this method to use a custom {@link Executor}, which
    * may configure its worker thread with a specific name, thread group or
    * priority. The returned executor's {@link Executor#execute(Runnable)
    * execute()} method is called when this service is started, and should return
    * promptly.
    * 
    * <p>The default implementation returns a new {@link Executor} that sets the 
    * name of its threads to the string returned by {@link #serviceName}
    */
   protected Executor executor() {
     return new Executor() {
       @Override
       public void execute(Runnable command) {
         MoreExecutors.newThread(serviceName(), command).start();
       }
     };
   }
 
   @Override public String toString() {
     return serviceName() + " [" + state() + "]";
   }
 
   @Override public final boolean isRunning() {
     return delegate.isRunning();
   }
 
   @Override public final State state() {
     return delegate.state();
   }
 
   /**
    * @since 13.0
    */
   @Override public final void addListener(Listener listener, Executor executor) {
     delegate.addListener(listener, executor);
   }
   
   /**
    * @since 14.0
    */
   @Override public final Throwable failureCause() {
     return delegate.failureCause();
   }
   
   /**
    * @since 15.0
    */
   @Override public final Service startAsync() {
     delegate.startAsync();
     return this;
   }
   
   /**
    * @since 15.0
    */
   @Override public final Service stopAsync() {
     delegate.stopAsync();
     return this;
   }
   
   /**
    * @since 15.0
    */
   @Override public final void awaitRunning() {
     delegate.awaitRunning();
   }
   
   /**
    * @since 15.0
    */
   @Override public final void awaitRunning(long timeout, TimeUnit unit) throws TimeoutException {
     delegate.awaitRunning(timeout, unit);
   }
   
   /**
    * @since 15.0
    */
   @Override public final void awaitTerminated() {
     delegate.awaitTerminated();
   }
   
   /**
    * @since 15.0
    */
   @Override public final void awaitTerminated(long timeout, TimeUnit unit) throws TimeoutException {
     delegate.awaitTerminated(timeout, unit);
   }
   
   /**
    * Returns the name of this service. {@link AbstractExecutionThreadService}
    * may include the name in debugging output.
    *
    * <p>Subclasses may override this method.
    *
    * @since 14.0 (present in 10.0 as getServiceName)
    */
   protected String serviceName() {
     return getClass().getSimpleName();
   }
 }