/*
 * 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:
 *
 *   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.
 */
package io.netty.channel;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufAllocator;
import io.netty.util.UncheckedBooleanSupplier;

Default implementation of MaxMessagesRecvByteBufAllocator which respects ChannelConfig.isAutoRead() and also prevents overflow. /**
 * Default implementation of {@link MaxMessagesRecvByteBufAllocator} which respects {@link ChannelConfig#isAutoRead()}
 * and also prevents overflow.
 */
public abstract class DefaultMaxMessagesRecvByteBufAllocator implements MaxMessagesRecvByteBufAllocator {
    private volatile int maxMessagesPerRead;
    private volatile boolean respectMaybeMoreData = true;

    public DefaultMaxMessagesRecvByteBufAllocator() {
        this(1);
    }

    public DefaultMaxMessagesRecvByteBufAllocator(int maxMessagesPerRead) {
        maxMessagesPerRead(maxMessagesPerRead);
    }

    @Override
    public int maxMessagesPerRead() {
        return maxMessagesPerRead;
    }

    @Override
    public MaxMessagesRecvByteBufAllocator maxMessagesPerRead(int maxMessagesPerRead) {
        if (maxMessagesPerRead <= 0) {
            throw new IllegalArgumentException("maxMessagesPerRead: " + maxMessagesPerRead + " (expected: > 0)");
        }
        this.maxMessagesPerRead = maxMessagesPerRead;
        return this;
    }

    
Determine if future instances of RecvByteBufAllocator.newHandle() will stop reading if we think there is no more data. 
Params:
respectMaybeMoreData – 

    
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 maxMessagesPerRead() quantum and have to wait for the selector to notify us of more data.
    
false to keep reading (up to maxMessagesPerRead()) or until there is no data when we attempt to read.
Returns:
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 RecvByteBufAllocator.newHandle() will stop reading if we think there is no more data. 
Returns:


    
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 maxMessagesPerRead() quantum and have to wait for the selector to notify us of more data.
    
false to keep reading (up to maxMessagesPerRead()) or until there is no data when we attempt to read.
/**
     * 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 continueReading(). /**
     * 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 ChannelConfig.getMaxMessagesPerRead() is used. /**
         * 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 &&
                   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;
        }
    }
}