/*
    * 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;
  
  import static io.netty.util.internal.ObjectUtil.checkPositive;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.ByteBufAllocator;
  import io.netty.util.UncheckedBooleanSupplier;
  
  /**
   * Default implementation of {@link MaxMessagesRecvByteBufAllocator} which respects {@link ChannelConfig#isAutoRead()}
   * and also prevents overflow.
   */
  public abstract class DefaultMaxMessagesRecvByteBufAllocator implements MaxMessagesRecvByteBufAllocator {
      private final boolean ignoreBytesRead;
      private volatile int maxMessagesPerRead;
      private volatile boolean respectMaybeMoreData = true;
  
      public DefaultMaxMessagesRecvByteBufAllocator() {
          this(1);
      }
  
      public DefaultMaxMessagesRecvByteBufAllocator(int maxMessagesPerRead) {
          this(maxMessagesPerRead, false);
      }
  
      DefaultMaxMessagesRecvByteBufAllocator(int maxMessagesPerRead, boolean ignoreBytesRead) {
          this.ignoreBytesRead = ignoreBytesRead;
          maxMessagesPerRead(maxMessagesPerRead);
      }
  
      @Override
      public int maxMessagesPerRead() {
          return maxMessagesPerRead;
      }
  
      @Override
      public MaxMessagesRecvByteBufAllocator maxMessagesPerRead(int maxMessagesPerRead) {
          checkPositive(maxMessagesPerRead, "maxMessagesPerRead");
          this.maxMessagesPerRead = maxMessagesPerRead;
          return this;
      }
  
      /**
       * Determine if future instances of {@link #newHandle()} will stop reading if we think there is no more data.
       * @param respectMaybeMoreData
       * <ul>
       *     <li>{@code true} to stop reading if we think there is no more data. This may save a system call to read from
       *          the socket, but if data has arrived in a racy fashion we may give up our {@link #maxMessagesPerRead()}
       *          quantum and have to wait for the selector to notify us of more data.</li>
       *     <li>{@code false} to keep reading (up to {@link #maxMessagesPerRead()}) or until there is no data when we
       *          attempt to read.</li>
       * </ul>
       * @return {@code this}.
       */
      public DefaultMaxMessagesRecvByteBufAllocator respectMaybeMoreData(boolean respectMaybeMoreData) {
          this.respectMaybeMoreData = respectMaybeMoreData;
          return this;
      }
  
      /**
       * Get if future instances of {@link #newHandle()} will stop reading if we think there is no more data.
       * @return
       * <ul>
       *     <li>{@code true} to stop reading if we think there is no more data. This may save a system call to read from
       *          the socket, but if data has arrived in a racy fashion we may give up our {@link #maxMessagesPerRead()}
       *          quantum and have to wait for the selector to notify us of more data.</li>
       *     <li>{@code false} to keep reading (up to {@link #maxMessagesPerRead()}) or until there is no data when we
       *          attempt to read.</li>
       * </ul>
       */
      public final boolean respectMaybeMoreData() {
          return respectMaybeMoreData;
      }
  
      /**
       * Focuses on enforcing the maximum messages per read condition for {@link #continueReading()}.
       */
      public abstract class MaxMessageHandle implements ExtendedHandle {
          private ChannelConfig config;
          private int maxMessagePerRead;
          private int totalMessages;
          private int totalBytesRead;
          private int attemptedBytesRead;
          private int lastBytesRead;
         private final boolean respectMaybeMoreData = DefaultMaxMessagesRecvByteBufAllocator.this.respectMaybeMoreData;
         private final UncheckedBooleanSupplier defaultMaybeMoreSupplier = new UncheckedBooleanSupplier() {
             @Override
             public boolean get() {
                 return attemptedBytesRead == lastBytesRead;
             }
         };
 
         /**
          * Only {@link ChannelConfig#getMaxMessagesPerRead()} is used.
          */
         @Override
         public void reset(ChannelConfig config) {
             this.config = config;
             maxMessagePerRead = maxMessagesPerRead();
             totalMessages = totalBytesRead = 0;
         }
 
         @Override
         public ByteBuf allocate(ByteBufAllocator alloc) {
             return alloc.ioBuffer(guess());
         }
 
         @Override
         public final void incMessagesRead(int amt) {
             totalMessages += amt;
         }
 
         @Override
         public void lastBytesRead(int bytes) {
             lastBytesRead = bytes;
             if (bytes > 0) {
                 totalBytesRead += bytes;
             }
         }
 
         @Override
         public final int lastBytesRead() {
             return lastBytesRead;
         }
 
         @Override
         public boolean continueReading() {
             return continueReading(defaultMaybeMoreSupplier);
         }
 
         @Override
         public boolean continueReading(UncheckedBooleanSupplier maybeMoreDataSupplier) {
             return config.isAutoRead() &&
                    (!respectMaybeMoreData || maybeMoreDataSupplier.get()) &&
                    totalMessages < maxMessagePerRead && (ignoreBytesRead || totalBytesRead > 0);
         }
 
         @Override
         public void readComplete() {
         }
 
         @Override
         public int attemptedBytesRead() {
             return attemptedBytesRead;
         }
 
         @Override
         public void attemptedBytesRead(int bytes) {
             attemptedBytesRead = bytes;
         }
 
         protected final int totalBytesRead() {
             return totalBytesRead < 0 ? Integer.MAX_VALUE : totalBytesRead;
         }
     }
 }