/*
    * 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.channel.pool;
  
  import static io.netty.util.internal.ObjectUtil.checkPositive;
  
  import io.netty.bootstrap.Bootstrap;
  import io.netty.channel.Channel;
  import io.netty.util.concurrent.EventExecutor;
  import io.netty.util.concurrent.Future;
  import io.netty.util.concurrent.FutureListener;
  import io.netty.util.concurrent.GlobalEventExecutor;
  import io.netty.util.concurrent.Promise;
  import io.netty.util.internal.ObjectUtil;
  
  import java.nio.channels.ClosedChannelException;
  import java.util.ArrayDeque;
  import java.util.Queue;
  import java.util.concurrent.atomic.AtomicInteger;
  import java.util.concurrent.Callable;
  import java.util.concurrent.ScheduledFuture;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.TimeoutException;
  
  /**
   * {@link ChannelPool} implementation that takes another {@link ChannelPool} implementation and enforce a maximum
   * number of concurrent connections.
   */
  public class FixedChannelPool extends SimpleChannelPool {
  
      public enum AcquireTimeoutAction {
          /**
           * Create a new connection when the timeout is detected.
           */
          NEW,
  
          /**
           * Fail the {@link Future} of the acquire call with a {@link TimeoutException}.
           */
          FAIL
      }
  
      private final EventExecutor executor;
      private final long acquireTimeoutNanos;
      private final Runnable timeoutTask;
  
      // There is no need to worry about synchronization as everything that modified the queue or counts is done
      // by the above EventExecutor.
      private final Queue<AcquireTask> pendingAcquireQueue = new ArrayDeque<AcquireTask>();
      private final int maxConnections;
      private final int maxPendingAcquires;
      private final AtomicInteger acquiredChannelCount = new AtomicInteger();
      private int pendingAcquireCount;
      private boolean closed;
  
      /**
       * Creates a new instance using the {@link ChannelHealthChecker#ACTIVE}.
       *
       * @param bootstrap         the {@link Bootstrap} that is used for connections
       * @param handler           the {@link ChannelPoolHandler} that will be notified for the different pool actions
       * @param maxConnections    the number of maximal active connections, once this is reached new tries to acquire
       *                          a {@link Channel} will be delayed until a connection is returned to the pool again.
       */
      public FixedChannelPool(Bootstrap bootstrap,
                              ChannelPoolHandler handler, int maxConnections) {
          this(bootstrap, handler, maxConnections, Integer.MAX_VALUE);
      }
  
      /**
       * Creates a new instance using the {@link ChannelHealthChecker#ACTIVE}.
       *
       * @param bootstrap             the {@link Bootstrap} that is used for connections
       * @param handler               the {@link ChannelPoolHandler} that will be notified for the different pool actions
       * @param maxConnections        the number of maximal active connections, once this is reached new tries to
       *                              acquire a {@link Channel} will be delayed until a connection is returned to the
       *                              pool again.
       * @param maxPendingAcquires    the maximum number of pending acquires. Once this is exceed acquire tries will
       *                              be failed.
       */
      public FixedChannelPool(Bootstrap bootstrap,
                              ChannelPoolHandler handler, int maxConnections, int maxPendingAcquires) {
          this(bootstrap, handler, ChannelHealthChecker.ACTIVE, null, -1, maxConnections, maxPendingAcquires);
      }
  
      /**
       * Creates a new instance.
      *
      * @param bootstrap             the {@link Bootstrap} that is used for connections
      * @param handler               the {@link ChannelPoolHandler} that will be notified for the different pool actions
      * @param healthCheck           the {@link ChannelHealthChecker} that will be used to check if a {@link Channel} is
      *                              still healthy when obtain from the {@link ChannelPool}
      * @param action                the {@link AcquireTimeoutAction} to use or {@code null} if non should be used.
      *                              In this case {@param acquireTimeoutMillis} must be {@code -1}.
      * @param acquireTimeoutMillis  the time (in milliseconds) after which an pending acquire must complete or
      *                              the {@link AcquireTimeoutAction} takes place.
      * @param maxConnections        the number of maximal active connections, once this is reached new tries to
      *                              acquire a {@link Channel} will be delayed until a connection is returned to the
      *                              pool again.
      * @param maxPendingAcquires    the maximum number of pending acquires. Once this is exceed acquire tries will
      *                              be failed.
      */
     public FixedChannelPool(Bootstrap bootstrap,
                             ChannelPoolHandler handler,
                             ChannelHealthChecker healthCheck, AcquireTimeoutAction action,
                             final long acquireTimeoutMillis,
                             int maxConnections, int maxPendingAcquires) {
         this(bootstrap, handler, healthCheck, action, acquireTimeoutMillis, maxConnections, maxPendingAcquires, true);
     }
 
     /**
      * Creates a new instance.
      *
      * @param bootstrap             the {@link Bootstrap} that is used for connections
      * @param handler               the {@link ChannelPoolHandler} that will be notified for the different pool actions
      * @param healthCheck           the {@link ChannelHealthChecker} that will be used to check if a {@link Channel} is
      *                              still healthy when obtain from the {@link ChannelPool}
      * @param action                the {@link AcquireTimeoutAction} to use or {@code null} if non should be used.
      *                              In this case {@param acquireTimeoutMillis} must be {@code -1}.
      * @param acquireTimeoutMillis  the time (in milliseconds) after which an pending acquire must complete or
      *                              the {@link AcquireTimeoutAction} takes place.
      * @param maxConnections        the number of maximal active connections, once this is reached new tries to
      *                              acquire a {@link Channel} will be delayed until a connection is returned to the
      *                              pool again.
      * @param maxPendingAcquires    the maximum number of pending acquires. Once this is exceed acquire tries will
      *                              be failed.
      * @param releaseHealthCheck    will check channel health before offering back if this parameter set to
      *                              {@code true}.
      */
     public FixedChannelPool(Bootstrap bootstrap,
                             ChannelPoolHandler handler,
                             ChannelHealthChecker healthCheck, AcquireTimeoutAction action,
                             final long acquireTimeoutMillis,
                             int maxConnections, int maxPendingAcquires, final boolean releaseHealthCheck) {
         this(bootstrap, handler, healthCheck, action, acquireTimeoutMillis, maxConnections, maxPendingAcquires,
                 releaseHealthCheck, true);
     }
 
     /**
      * Creates a new instance.
      *
      * @param bootstrap             the {@link Bootstrap} that is used for connections
      * @param handler               the {@link ChannelPoolHandler} that will be notified for the different pool actions
      * @param healthCheck           the {@link ChannelHealthChecker} that will be used to check if a {@link Channel} is
      *                              still healthy when obtain from the {@link ChannelPool}
      * @param action                the {@link AcquireTimeoutAction} to use or {@code null} if non should be used.
      *                              In this case {@param acquireTimeoutMillis} must be {@code -1}.
      * @param acquireTimeoutMillis  the time (in milliseconds) after which an pending acquire must complete or
      *                              the {@link AcquireTimeoutAction} takes place.
      * @param maxConnections        the number of maximal active connections, once this is reached new tries to
      *                              acquire a {@link Channel} will be delayed until a connection is returned to the
      *                              pool again.
      * @param maxPendingAcquires    the maximum number of pending acquires. Once this is exceed acquire tries will
      *                              be failed.
      * @param releaseHealthCheck    will check channel health before offering back if this parameter set to
      *                              {@code true}.
      * @param lastRecentUsed        {@code true} {@link Channel} selection will be LIFO, if {@code false} FIFO.
      */
     public FixedChannelPool(Bootstrap bootstrap,
                             ChannelPoolHandler handler,
                             ChannelHealthChecker healthCheck, AcquireTimeoutAction action,
                             final long acquireTimeoutMillis,
                             int maxConnections, int maxPendingAcquires,
                             boolean releaseHealthCheck, boolean lastRecentUsed) {
         super(bootstrap, handler, healthCheck, releaseHealthCheck, lastRecentUsed);
         checkPositive(maxConnections, "maxConnections");
         checkPositive(maxPendingAcquires, "maxPendingAcquires");
         if (action == null && acquireTimeoutMillis == -1) {
             timeoutTask = null;
             acquireTimeoutNanos = -1;
         } else if (action == null && acquireTimeoutMillis != -1) {
             throw new NullPointerException("action");
         } else if (action != null && acquireTimeoutMillis < 0) {
             throw new IllegalArgumentException("acquireTimeoutMillis: " + acquireTimeoutMillis + " (expected: >= 0)");
         } else {
             acquireTimeoutNanos = TimeUnit.MILLISECONDS.toNanos(acquireTimeoutMillis);
             switch (action) {
             case FAIL:
                 timeoutTask = new TimeoutTask() {
                     @Override
                     public void onTimeout(AcquireTask task) {
                         // Fail the promise as we timed out.
                         task.promise.setFailure(new AcquireTimeoutException());
                     }
                 };
                 break;
             case NEW:
                 timeoutTask = new TimeoutTask() {
                     @Override
                     public void onTimeout(AcquireTask task) {
                         // Increment the acquire count and delegate to super to actually acquire a Channel which will
                         // create a new connection.
                         task.acquired();
 
                         FixedChannelPool.super.acquire(task.promise);
                     }
                 };
                 break;
             default:
                 throw new Error("Unexpected AcquireTimeoutAction: " + action);
             }
         }
         executor = bootstrap.config().group().next();
         this.maxConnections = maxConnections;
         this.maxPendingAcquires = maxPendingAcquires;
     }
 
     /** Returns the number of acquired channels that this pool thinks it has. */
     public int acquiredChannelCount() {
         return acquiredChannelCount.get();
     }
 
     @Override
     public Future<Channel> acquire(final Promise<Channel> promise) {
         try {
             if (executor.inEventLoop()) {
                 acquire0(promise);
             } else {
                 executor.execute(new Runnable() {
                     @Override
                     public void run() {
                         acquire0(promise);
                     }
                 });
             }
         } catch (Throwable cause) {
             promise.tryFailure(cause);
         }
         return promise;
     }
 
     private void acquire0(final Promise<Channel> promise) {
         try {
             assert executor.inEventLoop();
 
             if (closed) {
                 promise.setFailure(new IllegalStateException("FixedChannelPool was closed"));
                 return;
             }
             if (acquiredChannelCount.get() < maxConnections) {
                 assert acquiredChannelCount.get() >= 0;
 
                 // We need to create a new promise as we need to ensure the AcquireListener runs in the correct
                 // EventLoop
                 Promise<Channel> p = executor.newPromise();
                 AcquireListener l = new AcquireListener(promise);
                 l.acquired();
                 p.addListener(l);
                 super.acquire(p);
             } else {
                 if (pendingAcquireCount >= maxPendingAcquires) {
                     tooManyOutstanding(promise);
                 } else {
                     AcquireTask task = new AcquireTask(promise);
                     if (pendingAcquireQueue.offer(task)) {
                         ++pendingAcquireCount;
 
                         if (timeoutTask != null) {
                             task.timeoutFuture = executor.schedule(timeoutTask, acquireTimeoutNanos,
                                   TimeUnit.NANOSECONDS);
                         }
                     } else {
                         tooManyOutstanding(promise);
                     }
                 }
 
                 assert pendingAcquireCount > 0;
             }
         } catch (Throwable cause) {
             promise.tryFailure(cause);
         }
     }
 
     private void tooManyOutstanding(Promise<?> promise) {
         promise.setFailure(new IllegalStateException("Too many outstanding acquire operations"));
     }
 
     @Override
     public Future<Void> release(final Channel channel, final Promise<Void> promise) {
         ObjectUtil.checkNotNull(promise, "promise");
         final Promise<Void> p = executor.newPromise();
         super.release(channel, p.addListener((FutureListener<Void>) future -> {
             try {
                 assert executor.inEventLoop();
 
                 if (closed) {
                     // Since the pool is closed, we have no choice but to close the channel
                     channel.close();
                     promise.setFailure(new IllegalStateException("FixedChannelPool was closed"));
                     return;
                 }
 
                 if (future.isSuccess()) {
                     decrementAndRunTaskQueue();
                     promise.setSuccess(null);
                 } else {
                     Throwable cause = future.cause();
                     // Check if the exception was not because of we passed the Channel to the wrong pool.
                     if (!(cause instanceof IllegalArgumentException)) {
                         decrementAndRunTaskQueue();
                     }
                     promise.setFailure(future.cause());
                 }
             } catch (Throwable cause) {
                 promise.tryFailure(cause);
             }
         }));
         return promise;
     }
 
     private void decrementAndRunTaskQueue() {
         // We should never have a negative value.
         int currentCount = acquiredChannelCount.decrementAndGet();
         assert currentCount >= 0;
 
         // Run the pending acquire tasks before notify the original promise so if the user would
         // try to acquire again from the ChannelFutureListener and the pendingAcquireCount is >=
         // maxPendingAcquires we may be able to run some pending tasks first and so allow to add
         // more.
         runTaskQueue();
     }
 
     private void runTaskQueue() {
         while (acquiredChannelCount.get() < maxConnections) {
             AcquireTask task = pendingAcquireQueue.poll();
             if (task == null) {
                 break;
             }
 
             // Cancel the timeout if one was scheduled
             ScheduledFuture<?> timeoutFuture = task.timeoutFuture;
             if (timeoutFuture != null) {
                 timeoutFuture.cancel(false);
             }
 
             --pendingAcquireCount;
             task.acquired();
 
             super.acquire(task.promise);
         }
 
         // We should never have a negative value.
         assert pendingAcquireCount >= 0;
         assert acquiredChannelCount.get() >= 0;
     }
 
     // AcquireTask extends AcquireListener to reduce object creations and so GC pressure
     private final class AcquireTask extends AcquireListener {
         final Promise<Channel> promise;
         final long expireNanoTime = System.nanoTime() + acquireTimeoutNanos;
         ScheduledFuture<?> timeoutFuture;
 
         AcquireTask(Promise<Channel> promise) {
             super(promise);
             // We need to create a new promise as we need to ensure the AcquireListener runs in the correct
             // EventLoop.
             this.promise = executor.<Channel>newPromise().addListener(this);
         }
     }
 
     private abstract class TimeoutTask implements Runnable {
         @Override
         public final void run() {
             assert executor.inEventLoop();
             long nanoTime = System.nanoTime();
             for (;;) {
                 AcquireTask task = pendingAcquireQueue.peek();
                 // Compare nanoTime as descripted in the javadocs of System.nanoTime()
                 //
                 // See https://docs.oracle.com/javase/7/docs/api/java/lang/System.html#nanoTime()
                 // See https://github.com/netty/netty/issues/3705
                 if (task == null || nanoTime - task.expireNanoTime < 0) {
                     break;
                 }
                 pendingAcquireQueue.remove();
 
                 --pendingAcquireCount;
                 onTimeout(task);
             }
         }
 
         public abstract void onTimeout(AcquireTask task);
     }
 
     private class AcquireListener implements FutureListener<Channel> {
         private final Promise<Channel> originalPromise;
         protected boolean acquired;
 
         AcquireListener(Promise<Channel> originalPromise) {
             this.originalPromise = originalPromise;
         }
 
         @Override
         public void operationComplete(Future<Channel> future) throws Exception {
             try {
                 assert executor.inEventLoop();
 
                 if (closed) {
                     if (future.isSuccess()) {
                         // Since the pool is closed, we have no choice but to close the channel
                         future.getNow().close();
                     }
                     originalPromise.setFailure(new IllegalStateException("FixedChannelPool was closed"));
                     return;
                 }
 
                 if (future.isSuccess()) {
                     originalPromise.setSuccess(future.getNow());
                 } else {
                     if (acquired) {
                         decrementAndRunTaskQueue();
                     } else {
                         runTaskQueue();
                     }
 
                     originalPromise.setFailure(future.cause());
                 }
             } catch (Throwable cause) {
                 originalPromise.tryFailure(cause);
             }
         }
 
         public void acquired() {
             if (acquired) {
                 return;
             }
             acquiredChannelCount.incrementAndGet();
             acquired = true;
         }
     }
 
     @Override
     public void close() {
         try {
             closeAsync().await();
         } catch (InterruptedException e) {
             Thread.currentThread().interrupt();
             throw new RuntimeException(e);
         }
     }
 
     /**
      * Closes the pool in an async manner.
      *
      * @return Future which represents completion of the close task
      */
     @Override
     public Future<Void> closeAsync() {
         if (executor.inEventLoop()) {
             return close0();
         } else {
             final Promise<Void> closeComplete = executor.newPromise();
             executor.execute(new Runnable() {
                 @Override
                 public void run() {
                     close0().addListener((FutureListener<Void>) f -> {
                         if (f.isSuccess()) {
                             closeComplete.setSuccess(null);
                         } else {
                             closeComplete.setFailure(f.cause());
                         }
                     });
                 }
             });
             return closeComplete;
         }
     }
 
     private Future<Void> close0() {
         assert executor.inEventLoop();
 
         if (!closed) {
             closed = true;
             for (;;) {
                 AcquireTask task = pendingAcquireQueue.poll();
                 if (task == null) {
                     break;
                 }
                 ScheduledFuture<?> f = task.timeoutFuture;
                 if (f != null) {
                     f.cancel(false);
                 }
                 task.promise.setFailure(new ClosedChannelException());
             }
             acquiredChannelCount.set(0);
             pendingAcquireCount = 0;
 
             // Ensure we dispatch this on another Thread as close0 will be called from the EventExecutor and we need
             // to ensure we will not block in a EventExecutor.
             return GlobalEventExecutor.INSTANCE.submit(new Callable<Void>() {
                 @Override
                 public Void call() throws Exception {
                     FixedChannelPool.super.close();
                     return null;
                 }
             });
         }
 
         return GlobalEventExecutor.INSTANCE.newSucceededFuture(null);
     }
 
     private static final class AcquireTimeoutException extends TimeoutException {
 
         private AcquireTimeoutException() {
             super("Acquire operation took longer then configured maximum time");
         }
 
         // Suppress a warning since the method doesn't need synchronization
         @Override
         public Throwable fillInStackTrace() {
             return this;
         }
     }
 }