/*
    * Copyright 2015 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 io.netty.util.internal.DefaultPriorityQueue;
  import io.netty.util.internal.ObjectUtil;
  import io.netty.util.internal.PriorityQueue;
  
  import java.util.Comparator;
  import java.util.Queue;
  import java.util.concurrent.Callable;
  import java.util.concurrent.TimeUnit;
  
  /**
   * Abstract base class for {@link EventExecutor}s that want to support scheduling.
   */
  public abstract class AbstractScheduledEventExecutor extends AbstractEventExecutor {
      private static final Comparator<ScheduledFutureTask<?>> SCHEDULED_FUTURE_TASK_COMPARATOR =
              new Comparator<ScheduledFutureTask<?>>() {
                  @Override
                  public int compare(ScheduledFutureTask<?> o1, ScheduledFutureTask<?> o2) {
                      return o1.compareTo(o2);
                  }
              };
  
      private static final long START_TIME = System.nanoTime();
  
      static final Runnable WAKEUP_TASK = new Runnable() {
         @Override
         public void run() { } // Do nothing
      };
  
      PriorityQueue<ScheduledFutureTask<?>> scheduledTaskQueue;
  
      long nextTaskId;
  
      protected AbstractScheduledEventExecutor() {
      }
  
      protected AbstractScheduledEventExecutor(EventExecutorGroup parent) {
          super(parent);
      }
  
      /**
       * Get the current time in nanoseconds by this executor's clock. This is not the same as {@link System#nanoTime()}
       * for two reasons:
       *
       * <ul>
       *     <li>We apply a fixed offset to the {@link System#nanoTime() nanoTime}</li>
       *     <li>Implementations (in particular EmbeddedEventLoop) may use their own time source so they can control time
       *     for testing purposes.</li>
       * </ul>
       */
      protected long getCurrentTimeNanos() {
          return defaultCurrentTimeNanos();
      }
  
      /**
       * @deprecated Use the non-static {@link #getCurrentTimeNanos()} instead.
       */
      @Deprecated
      protected static long nanoTime() {
          return defaultCurrentTimeNanos();
      }
  
      static long defaultCurrentTimeNanos() {
          return System.nanoTime() - START_TIME;
      }
  
      static long deadlineNanos(long nanoTime, long delay) {
          long deadlineNanos = nanoTime + delay;
          // Guard against overflow
          return deadlineNanos < 0 ? Long.MAX_VALUE : deadlineNanos;
      }
  
      /**
       * Given an arbitrary deadline {@code deadlineNanos}, calculate the number of nano seconds from now
       * {@code deadlineNanos} would expire.
       * @param deadlineNanos An arbitrary deadline in nano seconds.
       * @return the number of nano seconds from now {@code deadlineNanos} would expire.
       */
      protected static long deadlineToDelayNanos(long deadlineNanos) {
          return ScheduledFutureTask.deadlineToDelayNanos(defaultCurrentTimeNanos(), deadlineNanos);
      }
  
      /**
      * The initial value used for delay and computations based upon a monatomic time source.
      * @return initial value used for delay and computations based upon a monatomic time source.
      */
     protected static long initialNanoTime() {
         return START_TIME;
     }
 
     PriorityQueue<ScheduledFutureTask<?>> scheduledTaskQueue() {
         if (scheduledTaskQueue == null) {
             scheduledTaskQueue = new DefaultPriorityQueue<ScheduledFutureTask<?>>(
                     SCHEDULED_FUTURE_TASK_COMPARATOR,
                     // Use same initial capacity as java.util.PriorityQueue
                     11);
         }
         return scheduledTaskQueue;
     }
 
     private static boolean isNullOrEmpty(Queue<ScheduledFutureTask<?>> queue) {
         return queue == null || queue.isEmpty();
     }
 
     /**
      * Cancel all scheduled tasks.
      *
      * This method MUST be called only when {@link #inEventLoop()} is {@code true}.
      */
     protected void cancelScheduledTasks() {
         assert inEventLoop();
         PriorityQueue<ScheduledFutureTask<?>> scheduledTaskQueue = this.scheduledTaskQueue;
         if (isNullOrEmpty(scheduledTaskQueue)) {
             return;
         }
 
         final ScheduledFutureTask<?>[] scheduledTasks =
                 scheduledTaskQueue.toArray(new ScheduledFutureTask<?>[0]);
 
         for (ScheduledFutureTask<?> task: scheduledTasks) {
             task.cancelWithoutRemove(false);
         }
 
         scheduledTaskQueue.clearIgnoringIndexes();
     }
 
     /**
      * @see #pollScheduledTask(long)
      */
     protected final Runnable pollScheduledTask() {
         return pollScheduledTask(getCurrentTimeNanos());
     }
 
     /**
      * Return the {@link Runnable} which is ready to be executed with the given {@code nanoTime}.
      * You should use {@link #getCurrentTimeNanos()} to retrieve the correct {@code nanoTime}.
      */
     protected final Runnable pollScheduledTask(long nanoTime) {
         assert inEventLoop();
 
         ScheduledFutureTask<?> scheduledTask = peekScheduledTask();
         if (scheduledTask == null || scheduledTask.deadlineNanos() - nanoTime > 0) {
             return null;
         }
         scheduledTaskQueue.remove();
         scheduledTask.setConsumed();
         return scheduledTask;
     }
 
     /**
      * Return the nanoseconds until the next scheduled task is ready to be run or {@code -1} if no task is scheduled.
      */
     protected final long nextScheduledTaskNano() {
         ScheduledFutureTask<?> scheduledTask = peekScheduledTask();
         return scheduledTask != null ? scheduledTask.delayNanos() : -1;
     }
 
     /**
      * Return the deadline (in nanoseconds) when the next scheduled task is ready to be run or {@code -1}
      * if no task is scheduled.
      */
     protected final long nextScheduledTaskDeadlineNanos() {
         ScheduledFutureTask<?> scheduledTask = peekScheduledTask();
         return scheduledTask != null ? scheduledTask.deadlineNanos() : -1;
     }
 
     final ScheduledFutureTask<?> peekScheduledTask() {
         Queue<ScheduledFutureTask<?>> scheduledTaskQueue = this.scheduledTaskQueue;
         return scheduledTaskQueue != null ? scheduledTaskQueue.peek() : null;
     }
 
     /**
      * Returns {@code true} if a scheduled task is ready for processing.
      */
     protected final boolean hasScheduledTasks() {
         ScheduledFutureTask<?> scheduledTask = peekScheduledTask();
         return scheduledTask != null && scheduledTask.deadlineNanos() <= getCurrentTimeNanos();
     }
 
     @Override
     public ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit) {
         ObjectUtil.checkNotNull(command, "command");
         ObjectUtil.checkNotNull(unit, "unit");
         if (delay < 0) {
             delay = 0;
         }
         validateScheduled0(delay, unit);
 
         return schedule(new ScheduledFutureTask<Void>(
                 this,
                 command,
                 deadlineNanos(getCurrentTimeNanos(), unit.toNanos(delay))));
     }
 
     @Override
     public <V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit) {
         ObjectUtil.checkNotNull(callable, "callable");
         ObjectUtil.checkNotNull(unit, "unit");
         if (delay < 0) {
             delay = 0;
         }
         validateScheduled0(delay, unit);
 
         return schedule(new ScheduledFutureTask<V>(
                 this, callable, deadlineNanos(getCurrentTimeNanos(), unit.toNanos(delay))));
     }
 
     @Override
     public ScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit) {
         ObjectUtil.checkNotNull(command, "command");
         ObjectUtil.checkNotNull(unit, "unit");
         if (initialDelay < 0) {
             throw new IllegalArgumentException(
                     String.format("initialDelay: %d (expected: >= 0)", initialDelay));
         }
         if (period <= 0) {
             throw new IllegalArgumentException(
                     String.format("period: %d (expected: > 0)", period));
         }
         validateScheduled0(initialDelay, unit);
         validateScheduled0(period, unit);
 
         return schedule(new ScheduledFutureTask<Void>(
                 this, command, deadlineNanos(getCurrentTimeNanos(), unit.toNanos(initialDelay)), unit.toNanos(period)));
     }
 
     @Override
     public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit) {
         ObjectUtil.checkNotNull(command, "command");
         ObjectUtil.checkNotNull(unit, "unit");
         if (initialDelay < 0) {
             throw new IllegalArgumentException(
                     String.format("initialDelay: %d (expected: >= 0)", initialDelay));
         }
         if (delay <= 0) {
             throw new IllegalArgumentException(
                     String.format("delay: %d (expected: > 0)", delay));
         }
 
         validateScheduled0(initialDelay, unit);
         validateScheduled0(delay, unit);
 
         return schedule(new ScheduledFutureTask<Void>(
                 this, command, deadlineNanos(getCurrentTimeNanos(), unit.toNanos(initialDelay)), -unit.toNanos(delay)));
     }
 
     @SuppressWarnings("deprecation")
     private void validateScheduled0(long amount, TimeUnit unit) {
         validateScheduled(amount, unit);
     }
 
     /**
      * Sub-classes may override this to restrict the maximal amount of time someone can use to schedule a task.
      *
      * @deprecated will be removed in the future.
      */
     @Deprecated
     protected void validateScheduled(long amount, TimeUnit unit) {
         // NOOP
     }
 
     final void scheduleFromEventLoop(final ScheduledFutureTask<?> task) {
         // nextTaskId a long and so there is no chance it will overflow back to 0
         scheduledTaskQueue().add(task.setId(++nextTaskId));
     }
 
     private <V> ScheduledFuture<V> schedule(final ScheduledFutureTask<V> task) {
         if (inEventLoop()) {
             scheduleFromEventLoop(task);
         } else {
             final long deadlineNanos = task.deadlineNanos();
             // task will add itself to scheduled task queue when run if not expired
             if (beforeScheduledTaskSubmitted(deadlineNanos)) {
                 execute(task);
             } else {
                 lazyExecute(task);
                 // Second hook after scheduling to facilitate race-avoidance
                 if (afterScheduledTaskSubmitted(deadlineNanos)) {
                     execute(WAKEUP_TASK);
                 }
             }
         }
 
         return task;
     }
 
     final void removeScheduled(final ScheduledFutureTask<?> task) {
         assert task.isCancelled();
         if (inEventLoop()) {
             scheduledTaskQueue().removeTyped(task);
         } else {
             // task will remove itself from scheduled task queue when it runs
             scheduleRemoveScheduled(task);
         }
     }
 
     void scheduleRemoveScheduled(final ScheduledFutureTask<?> task) {
         // task will remove itself from scheduled task queue when it runs
         lazyExecute(task);
     }
 
     /**
      * Called from arbitrary non-{@link EventExecutor} threads prior to scheduled task submission.
      * Returns {@code true} if the {@link EventExecutor} thread should be woken immediately to
      * process the scheduled task (if not already awake).
      * <p>
      * If {@code false} is returned, {@link #afterScheduledTaskSubmitted(long)} will be called with
      * the same value <i>after</i> the scheduled task is enqueued, providing another opportunity
      * to wake the {@link EventExecutor} thread if required.
      *
      * @param deadlineNanos deadline of the to-be-scheduled task
      *     relative to {@link AbstractScheduledEventExecutor#getCurrentTimeNanos()}
      * @return {@code true} if the {@link EventExecutor} thread should be woken, {@code false} otherwise
      */
     protected boolean beforeScheduledTaskSubmitted(long deadlineNanos) {
         return true;
     }
 
     /**
      * See {@link #beforeScheduledTaskSubmitted(long)}. Called only after that method returns false.
      *
      * @param deadlineNanos relative to {@link AbstractScheduledEventExecutor#getCurrentTimeNanos()}
      * @return  {@code true} if the {@link EventExecutor} thread should be woken, {@code false} otherwise
      */
     protected boolean afterScheduledTaskSubmitted(long deadlineNanos) {
         return true;
     }
 }