/*
    * ====================================================================
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you 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.
   * ====================================================================
   *
   * This software consists of voluntary contributions made by many
   * individuals on behalf of the Apache Software Foundation.  For more
   * information on the Apache Software Foundation, please see
   * <http://www.apache.org/>.
   *
   */
  package org.apache.http.concurrent;
  
  import org.apache.http.util.Args;
  
  import java.util.concurrent.CancellationException;
  import java.util.concurrent.ExecutionException;
  import java.util.concurrent.Future;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.TimeoutException;
  
  /**
   * Basic implementation of the {@link Future} interface. {@code BasicFuture}
   * can be put into a completed state by invoking any of the following methods:
   * {@link #cancel()}, {@link #failed(Exception)}, or {@link #completed(Object)}.
   *
   * @param <T> the future result type of an asynchronous operation.
   * @since 4.2
   */
  public class BasicFuture<T> implements Future<T>, Cancellable {
  
      private final FutureCallback<T> callback;
  
      private volatile boolean completed;
      private volatile boolean cancelled;
      private volatile T result;
      private volatile Exception ex;
  
      public BasicFuture(final FutureCallback<T> callback) {
          super();
          this.callback = callback;
      }
  
      @Override
      public boolean isCancelled() {
          return this.cancelled;
      }
  
      @Override
      public boolean isDone() {
          return this.completed;
      }
  
      private T getResult() throws ExecutionException {
          if (this.ex != null) {
              throw new ExecutionException(this.ex);
          }
          if (cancelled) {
              throw new CancellationException();
          }
          return this.result;
      }
  
      @Override
      public synchronized T get() throws InterruptedException, ExecutionException {
          while (!this.completed) {
              wait();
          }
          return getResult();
      }
  
      @Override
      public synchronized T get(final long timeout, final TimeUnit unit)
              throws InterruptedException, ExecutionException, TimeoutException {
          Args.notNull(unit, "Time unit");
          final long msecs = unit.toMillis(timeout);
          final long startTime = (msecs <= 0) ? 0 : System.currentTimeMillis();
          long waitTime = msecs;
          if (this.completed) {
              return getResult();
          } else if (waitTime <= 0) {
              throw new TimeoutException();
          } else {
              for (;;) {
                 wait(waitTime);
                 if (this.completed) {
                     return getResult();
                 }
                 waitTime = msecs - (System.currentTimeMillis() - startTime);
                 if (waitTime <= 0) {
                     throw new TimeoutException();
                 }
             }
         }
     }
 
     public boolean completed(final T result) {
         synchronized(this) {
             if (this.completed) {
                 return false;
             }
             this.completed = true;
             this.result = result;
             notifyAll();
         }
         if (this.callback != null) {
             this.callback.completed(result);
         }
         return true;
     }
 
     public boolean failed(final Exception exception) {
         synchronized(this) {
             if (this.completed) {
                 return false;
             }
             this.completed = true;
             this.ex = exception;
             notifyAll();
         }
         if (this.callback != null) {
             this.callback.failed(exception);
         }
         return true;
     }
 
     @Override
     public boolean cancel(final boolean mayInterruptIfRunning) {
         synchronized(this) {
             if (this.completed) {
                 return false;
             }
             this.completed = true;
             this.cancelled = true;
             notifyAll();
         }
         if (this.callback != null) {
             this.callback.cancelled();
         }
         return true;
     }
 
     @Override
     public boolean cancel() {
         return cancel(true);
     }
 
 }