/*
 * Copyright 2012 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.ByteBufAllocator;
import io.netty.channel.ChannelHandler.Skip;
import io.netty.util.Attribute;
import io.netty.util.AttributeKey;
import io.netty.util.ReferenceCountUtil;
import io.netty.util.ResourceLeakHint;
import io.netty.util.concurrent.EventExecutor;
import io.netty.util.internal.PlatformDependent;
import io.netty.util.internal.StringUtil;

import java.net.SocketAddress;
import java.util.WeakHashMap;

final class DefaultChannelHandlerContext implements ChannelHandlerContext, ResourceLeakHint {

    // This class keeps an integer member field 'skipFlags' whose each bit tells if the corresponding handler method
    // is annotated with @Skip. 'skipFlags' is retrieved in runtime via the reflection API and is cached.
    // The following constants signify which bit of 'skipFlags' corresponds to which handler method:

    static final int MASK_HANDLER_ADDED = 1;
    static final int MASK_HANDLER_REMOVED = 1 << 1;
    private static final int MASK_EXCEPTION_CAUGHT = 1 << 2;
    private static final int MASK_CHANNEL_REGISTERED = 1 << 3;
    private static final int MASK_CHANNEL_ACTIVE = 1 << 4;
    private static final int MASK_CHANNEL_INACTIVE = 1 << 5;
    private static final int MASK_CHANNEL_READ = 1 << 6;
    private static final int MASK_CHANNEL_READ_COMPLETE = 1 << 7;
    private static final int MASK_CHANNEL_WRITABILITY_CHANGED = 1 << 8;
    private static final int MASK_USER_EVENT_TRIGGERED = 1 << 9;
    private static final int MASK_BIND = 1 << 10;
    private static final int MASK_CONNECT = 1 << 11;
    private static final int MASK_DISCONNECT = 1 << 12;
    private static final int MASK_CLOSE = 1 << 13;
    private static final int MASK_READ = 1 << 14;
    private static final int MASK_WRITE = 1 << 15;
    private static final int MASK_FLUSH = 1 << 16;

    /**
     * Cache the result of the costly generation of {@link #skipFlags} in the partitioned synchronized
     * {@link WeakHashMap}.
     */
    @SuppressWarnings("unchecked")
    private static final WeakHashMap<Class<?>, Integer>[] skipFlagsCache =
            new WeakHashMap[Runtime.getRuntime().availableProcessors()];

    static {
        for (int i = 0; i < skipFlagsCache.length; i ++) {
            skipFlagsCache[i] = new WeakHashMap<Class<?>, Integer>();
        }
    }

    /**
     * Returns an integer bitset that tells which handler methods were annotated with {@link Skip}.
     * It gets the value from {@link #skipFlagsCache} if an handler of the same type were queried before.
     * Otherwise, it delegates to {@link #skipFlags0(Class)} to get it.
     */
    private static int skipFlags(ChannelHandler handler) {
        WeakHashMap<Class<?>, Integer> cache =
                skipFlagsCache[(int) (Thread.currentThread().getId() % skipFlagsCache.length)];
        Class<? extends ChannelHandler> handlerType = handler.getClass();
        int flagsVal;
        synchronized (cache) {
            Integer flags = cache.get(handlerType);
            if (flags != null) {
                flagsVal = flags;
            } else {
                flagsVal = skipFlags0(handlerType);
                cache.put(handlerType, Integer.valueOf(flagsVal));
            }
        }

        return flagsVal;
    }

    /**
     * Determines the {@link #skipFlags} of the specified {@code handlerType} using the reflection API.
     */
    private static int skipFlags0(Class<? extends ChannelHandler> handlerType) {
        int flags = 0;
        try {
            if (handlerType.getMethod(
                    "handlerAdded", ChannelHandlerContext.class).isAnnotationPresent(Skip.class)) {
                flags |= MASK_HANDLER_ADDED;
            }
            if (handlerType.getMethod(
                    "handlerRemoved", ChannelHandlerContext.class).isAnnotationPresent(Skip.class)) {
                flags |= MASK_HANDLER_REMOVED;
            }
            if (handlerType.getMethod(
                    "exceptionCaught", ChannelHandlerContext.class, Throwable.class).isAnnotationPresent(Skip.class)) {
                flags |= MASK_EXCEPTION_CAUGHT;
            }
            if (handlerType.getMethod(
                    "channelRegistered", ChannelHandlerContext.class).isAnnotationPresent(Skip.class)) {
                flags |= MASK_CHANNEL_REGISTERED;
            }
            if (handlerType.getMethod(
                    "channelActive", ChannelHandlerContext.class).isAnnotationPresent(Skip.class)) {
                flags |= MASK_CHANNEL_ACTIVE;
            }
            if (handlerType.getMethod(
                    "channelInactive", ChannelHandlerContext.class).isAnnotationPresent(Skip.class)) {
                flags |= MASK_CHANNEL_INACTIVE;
            }
            if (handlerType.getMethod(
                    "channelRead", ChannelHandlerContext.class, Object.class).isAnnotationPresent(Skip.class)) {
                flags |= MASK_CHANNEL_READ;
            }
            if (handlerType.getMethod(
                    "channelReadComplete", ChannelHandlerContext.class).isAnnotationPresent(Skip.class)) {
                flags |= MASK_CHANNEL_READ_COMPLETE;
            }
            if (handlerType.getMethod(
                    "channelWritabilityChanged", ChannelHandlerContext.class).isAnnotationPresent(Skip.class)) {
                flags |= MASK_CHANNEL_WRITABILITY_CHANGED;
            }
            if (handlerType.getMethod(
                    "userEventTriggered", ChannelHandlerContext.class, Object.class).isAnnotationPresent(Skip.class)) {
                flags |= MASK_USER_EVENT_TRIGGERED;
            }
            if (handlerType.getMethod(
                    "bind", ChannelHandlerContext.class,
                    SocketAddress.class, ChannelPromise.class).isAnnotationPresent(Skip.class)) {
                flags |= MASK_BIND;
            }
            if (handlerType.getMethod(
                    "connect", ChannelHandlerContext.class, SocketAddress.class, SocketAddress.class,
                    ChannelPromise.class).isAnnotationPresent(Skip.class)) {
                flags |= MASK_CONNECT;
            }
            if (handlerType.getMethod(
                    "disconnect", ChannelHandlerContext.class, ChannelPromise.class).isAnnotationPresent(Skip.class)) {
                flags |= MASK_DISCONNECT;
            }
            if (handlerType.getMethod(
                    "close", ChannelHandlerContext.class, ChannelPromise.class).isAnnotationPresent(Skip.class)) {
                flags |= MASK_CLOSE;
            }
            if (handlerType.getMethod(
                    "read", ChannelHandlerContext.class).isAnnotationPresent(Skip.class)) {
                flags |= MASK_READ;
            }
            if (handlerType.getMethod(
                    "write", ChannelHandlerContext.class,
                    Object.class, ChannelPromise.class).isAnnotationPresent(Skip.class)) {
                flags |= MASK_WRITE;

                // flush() is skipped only when write() is also skipped to avoid the situation where
                // flush() is handled by the event loop before write() in staged execution.
                if (handlerType.getMethod(
                        "flush", ChannelHandlerContext.class).isAnnotationPresent(Skip.class)) {
                    flags |= MASK_FLUSH;
                }
            }
        } catch (Exception e) {
            // Should never reach here.
            PlatformDependent.throwException(e);
        }

        return flags;
    }

    volatile DefaultChannelHandlerContext next;
    volatile DefaultChannelHandlerContext prev;

    private final AbstractChannel channel;
    private final DefaultChannelPipeline pipeline;
    private final String name;
    private final ChannelHandler handler;
    private boolean removed;

    final int skipFlags;

    // Will be set to null if no child executor should be used, otherwise it will be set to the
    // child executor.
    final ChannelHandlerInvoker invoker;
    private ChannelFuture succeededFuture;

    // Lazily instantiated tasks used to trigger events to a handler with different executor.
    Runnable invokeChannelReadCompleteTask;
    Runnable invokeReadTask;
    Runnable invokeFlushTask;
    Runnable invokeChannelWritableStateChangedTask;

    DefaultChannelHandlerContext(
            DefaultChannelPipeline pipeline, ChannelHandlerInvoker invoker, String name, ChannelHandler handler) {

        if (name == null) {
            throw new NullPointerException("name");
        }
        if (handler == null) {
            throw new NullPointerException("handler");
        }

        channel = pipeline.channel;
        this.pipeline = pipeline;
        this.name = name;
        this.handler = handler;

        skipFlags = skipFlags(handler);

        if (invoker == null) {
            this.invoker = channel.unsafe().invoker();
        } else {
            this.invoker = invoker;
        }
    }

    /** Invocation initiated by {@link DefaultChannelPipeline#teardownAll()}}. */
    void teardown() {
        EventExecutor executor = executor();
        if (executor.inEventLoop()) {
            teardown0();
        } else {
            executor.execute(new Runnable() {
                @Override
                public void run() {
                    teardown0();
                }
            });
        }
    }

    private void teardown0() {
        DefaultChannelHandlerContext prev = this.prev;
        if (prev != null) {
            synchronized (pipeline) {
                pipeline.remove0(this);
            }
            prev.teardown();
        }
    }

    @Override
    public Channel channel() {
        return channel;
    }

    @Override
    public ChannelPipeline pipeline() {
        return pipeline;
    }

    @Override
    public ByteBufAllocator alloc() {
        return channel().config().getAllocator();
    }

    @Override
    public EventExecutor executor() {
        return invoker.executor();
    }

    @Override
    public ChannelHandlerInvoker invoker() {
        return invoker;
    }

    @Override
    public ChannelHandler handler() {
        return handler;
    }

    @Override
    public String name() {
        return name;
    }

    @Override
    public <T> Attribute<T> attr(AttributeKey<T> key) {
        return channel.attr(key);
    }

    @Override
    public ChannelHandlerContext fireChannelRegistered() {
        DefaultChannelHandlerContext next = findContextInbound(MASK_CHANNEL_REGISTERED);
        next.invoker.invokeChannelRegistered(next);
        return this;
    }

    @Override
    public ChannelHandlerContext fireChannelActive() {
        DefaultChannelHandlerContext next = findContextInbound(MASK_CHANNEL_ACTIVE);
        next.invoker.invokeChannelActive(next);
        return this;
    }

    @Override
    public ChannelHandlerContext fireChannelInactive() {
        DefaultChannelHandlerContext next = findContextInbound(MASK_CHANNEL_INACTIVE);
        next.invoker.invokeChannelInactive(next);
        return this;
    }

    @Override
    public ChannelHandlerContext fireExceptionCaught(Throwable cause) {
        DefaultChannelHandlerContext next = findContextInbound(MASK_EXCEPTION_CAUGHT);
        next.invoker.invokeExceptionCaught(next, cause);
        return this;
    }

    @Override
    public ChannelHandlerContext fireUserEventTriggered(Object event) {
        DefaultChannelHandlerContext next = findContextInbound(MASK_USER_EVENT_TRIGGERED);
        next.invoker.invokeUserEventTriggered(next, event);
        return this;
    }

    @Override
    public ChannelHandlerContext fireChannelRead(Object msg) {
        DefaultChannelHandlerContext next = findContextInbound(MASK_CHANNEL_READ);
        ReferenceCountUtil.touch(msg, next);
        next.invoker.invokeChannelRead(next, msg);
        return this;
    }

    @Override
    public ChannelHandlerContext fireChannelReadComplete() {
        DefaultChannelHandlerContext next = findContextInbound(MASK_CHANNEL_READ_COMPLETE);
        next.invoker.invokeChannelReadComplete(next);
        return this;
    }

    @Override
    public ChannelHandlerContext fireChannelWritabilityChanged() {
        DefaultChannelHandlerContext next = findContextInbound(MASK_CHANNEL_WRITABILITY_CHANGED);
        next.invoker.invokeChannelWritabilityChanged(next);
        return this;
    }

    @Override
    public ChannelFuture bind(SocketAddress localAddress) {
        return bind(localAddress, newPromise());
    }

    @Override
    public ChannelFuture connect(SocketAddress remoteAddress) {
        return connect(remoteAddress, newPromise());
    }

    @Override
    public ChannelFuture connect(SocketAddress remoteAddress, SocketAddress localAddress) {
        return connect(remoteAddress, localAddress, newPromise());
    }

    @Override
    public ChannelFuture disconnect() {
        return disconnect(newPromise());
    }

    @Override
    public ChannelFuture close() {
        return close(newPromise());
    }

    @Override
    public ChannelFuture bind(final SocketAddress localAddress, final ChannelPromise promise) {
        DefaultChannelHandlerContext next = findContextOutbound(MASK_BIND);
        next.invoker.invokeBind(next, localAddress, promise);
        return promise;
    }

    @Override
    public ChannelFuture connect(SocketAddress remoteAddress, ChannelPromise promise) {
        return connect(remoteAddress, null, promise);
    }

    @Override
    public ChannelFuture connect(SocketAddress remoteAddress, SocketAddress localAddress, ChannelPromise promise) {
        DefaultChannelHandlerContext next = findContextOutbound(MASK_CONNECT);
        next.invoker.invokeConnect(next, remoteAddress, localAddress, promise);
        return promise;
    }

    @Override
    public ChannelFuture disconnect(ChannelPromise promise) {
        if (!channel().metadata().hasDisconnect()) {
            return close(promise);
        }

        DefaultChannelHandlerContext next = findContextOutbound(MASK_DISCONNECT);
        next.invoker.invokeDisconnect(next, promise);
        return promise;
    }

    @Override
    public ChannelFuture close(ChannelPromise promise) {
        DefaultChannelHandlerContext next = findContextOutbound(MASK_CLOSE);
        next.invoker.invokeClose(next, promise);
        return promise;
    }

    @Override
    public ChannelHandlerContext read() {
        DefaultChannelHandlerContext next = findContextOutbound(MASK_READ);
        next.invoker.invokeRead(next);
        return this;
    }

    @Override
    public ChannelFuture write(Object msg) {
        return write(msg, newPromise());
    }

    @Override
    public ChannelFuture write(Object msg, ChannelPromise promise) {
        DefaultChannelHandlerContext next = findContextOutbound(MASK_WRITE);
        ReferenceCountUtil.touch(msg, next);
        next.invoker.invokeWrite(next, msg, promise);
        return promise;
    }

    @Override
    public ChannelHandlerContext flush() {
        DefaultChannelHandlerContext next = findContextOutbound(MASK_FLUSH);
        next.invoker.invokeFlush(next);
        return this;
    }

    @Override
    public ChannelFuture writeAndFlush(Object msg, ChannelPromise promise) {
        DefaultChannelHandlerContext next;
        next = findContextOutbound(MASK_WRITE);
        ReferenceCountUtil.touch(msg, next);
        next.invoker.invokeWrite(next, msg, promise);
        next = findContextOutbound(MASK_FLUSH);
        next.invoker.invokeFlush(next);
        return promise;
    }

    @Override
    public ChannelFuture writeAndFlush(Object msg) {
        return writeAndFlush(msg, newPromise());
    }

    @Override
    public ChannelPromise newPromise() {
        return new DefaultChannelPromise(channel(), executor());
    }

    @Override
    public ChannelProgressivePromise newProgressivePromise() {
        return new DefaultChannelProgressivePromise(channel(), executor());
    }

    @Override
    public ChannelFuture newSucceededFuture() {
        ChannelFuture succeededFuture = this.succeededFuture;
        if (succeededFuture == null) {
            this.succeededFuture = succeededFuture = new SucceededChannelFuture(channel(), executor());
        }
        return succeededFuture;
    }

    @Override
    public ChannelFuture newFailedFuture(Throwable cause) {
        return new FailedChannelFuture(channel(), executor(), cause);
    }

    private DefaultChannelHandlerContext findContextInbound(int mask) {
        DefaultChannelHandlerContext ctx = this;
        do {
            ctx = ctx.next;
        } while ((ctx.skipFlags & mask) != 0);
        return ctx;
    }

    private DefaultChannelHandlerContext findContextOutbound(int mask) {
        DefaultChannelHandlerContext ctx = this;
        do {
            ctx = ctx.prev;
        } while ((ctx.skipFlags & mask) != 0);
        return ctx;
    }

    @Override
    public ChannelPromise voidPromise() {
        return channel.voidPromise();
    }

    void setRemoved() {
        removed = true;
    }

    @Override
    public boolean isRemoved() {
        return removed;
    }

    @Override
    public String toHintString() {
        return '\'' + name + "' will handle the message from this point.";
    }

    @Override
    public String toString() {
        return StringUtil.simpleClassName(ChannelHandlerContext.class) + '(' + name + ", " + channel + ')';
    }
}