/*
    * Copyright 2013 The Netty Project
    *
    * The Netty Project 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:
    *
    *   https://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 io.netty.util.concurrent;
  
  import java.util.concurrent.Callable;
  import java.util.concurrent.RunnableFuture;
  
  class PromiseTask<V> extends DefaultPromise<V> implements RunnableFuture<V> {
  
      private static final class RunnableAdapter<T> implements Callable<T> {
          final Runnable task;
          final T result;
  
          RunnableAdapter(Runnable task, T result) {
              this.task = task;
              this.result = result;
          }
  
          @Override
          public T call() {
              task.run();
              return result;
          }
  
          @Override
          public String toString() {
              return "Callable(task: " + task + ", result: " + result + ')';
          }
      }
  
      private static final Runnable COMPLETED = new SentinelRunnable("COMPLETED");
      private static final Runnable CANCELLED = new SentinelRunnable("CANCELLED");
      private static final Runnable FAILED = new SentinelRunnable("FAILED");
  
      private static class SentinelRunnable implements Runnable {
          private final String name;
  
          SentinelRunnable(String name) {
              this.name = name;
          }
  
          @Override
          public void run() { } // no-op
  
          @Override
          public String toString() {
              return name;
          }
      }
  
      // Strictly of type Callable<V> or Runnable
      private Object task;
  
      PromiseTask(EventExecutor executor, Runnable runnable, V result) {
          super(executor);
          task = result == null ? runnable : new RunnableAdapter<V>(runnable, result);
      }
  
      PromiseTask(EventExecutor executor, Runnable runnable) {
          super(executor);
          task = runnable;
      }
  
      PromiseTask(EventExecutor executor, Callable<V> callable) {
          super(executor);
          task = callable;
      }
  
      @Override
      public final int hashCode() {
          return System.identityHashCode(this);
      }
  
      @Override
      public final boolean equals(Object obj) {
          return this == obj;
      }
  
      @SuppressWarnings("unchecked")
      V runTask() throws Throwable {
          final Object task = this.task;
          if (task instanceof Callable) {
              return ((Callable<V>) task).call();
          }
          ((Runnable) task).run();
          return null;
     }
 
     @Override
     public void run() {
         try {
             if (setUncancellableInternal()) {
                 V result = runTask();
                 setSuccessInternal(result);
             }
         } catch (Throwable e) {
             setFailureInternal(e);
         }
     }
 
     private boolean clearTaskAfterCompletion(boolean done, Runnable result) {
         if (done) {
             // The only time where it might be possible for the sentinel task
             // to be called is in the case of a periodic ScheduledFutureTask,
             // in which case it's a benign race with cancellation and the (null)
             // return value is not used.
             task = result;
         }
         return done;
     }
 
     @Override
     public final Promise<V> setFailure(Throwable cause) {
         throw new IllegalStateException();
     }
 
     protected final Promise<V> setFailureInternal(Throwable cause) {
         super.setFailure(cause);
         clearTaskAfterCompletion(true, FAILED);
         return this;
     }
 
     @Override
     public final boolean tryFailure(Throwable cause) {
         return false;
     }
 
     protected final boolean tryFailureInternal(Throwable cause) {
         return clearTaskAfterCompletion(super.tryFailure(cause), FAILED);
     }
 
     @Override
     public final Promise<V> setSuccess(V result) {
         throw new IllegalStateException();
     }
 
     protected final Promise<V> setSuccessInternal(V result) {
         super.setSuccess(result);
         clearTaskAfterCompletion(true, COMPLETED);
         return this;
     }
 
     @Override
     public final boolean trySuccess(V result) {
         return false;
     }
 
     protected final boolean trySuccessInternal(V result) {
         return clearTaskAfterCompletion(super.trySuccess(result), COMPLETED);
     }
 
     @Override
     public final boolean setUncancellable() {
         throw new IllegalStateException();
     }
 
     protected final boolean setUncancellableInternal() {
         return super.setUncancellable();
     }
 
     @Override
     public boolean cancel(boolean mayInterruptIfRunning) {
         return clearTaskAfterCompletion(super.cancel(mayInterruptIfRunning), CANCELLED);
     }
 
     @Override
     protected StringBuilder toStringBuilder() {
         StringBuilder buf = super.toStringBuilder();
         buf.setCharAt(buf.length() - 1, ',');
 
         return buf.append(" task: ")
                   .append(task)
                   .append(')');
     }
 }