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/*
 * Copyright 2014 Netflix, Inc.
 *
 * Licensed 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.reactivex.netty.channel;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufAllocator;
import io.netty.channel.Channel;
import io.netty.channel.ChannelFuture;
import io.netty.channel.FileRegion;
import io.reactivex.netty.metrics.Clock;
import io.reactivex.netty.metrics.MetricEventsSubject;
import io.reactivex.netty.util.MultipleFutureListener;
import rx.Observable;
import rx.functions.Action0;
import rx.functions.Action1;

import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicReference;

/**
 * @author Nitesh Kant
 */
public class DefaultChannelWriter implements ChannelWriter {

    protected static final Observable CONNECTION_ALREADY_CLOSED =
            Observable.error(new IllegalStateException("Connection is already closed."));
    protected final AtomicBoolean closeIssued = new AtomicBoolean();

    private final Channel nettyChannel;

    /**
     * A listener for all pending writes before a flush.
     */
    private final AtomicReference unflushedWritesListener;
    @SuppressWarnings("rawtypes")private final MetricEventsSubject eventsSubject;
    private final ChannelMetricEventProvider metricEventProvider;

    protected DefaultChannelWriter(Channel nettyChannel, MetricEventsSubject eventsSubject,
                                   ChannelMetricEventProvider metricEventProvider) {
        this.eventsSubject = eventsSubject;
        this.metricEventProvider = metricEventProvider;
        if (null == nettyChannel) {
            throw new NullPointerException("Channel can not be null.");
        }
        this.nettyChannel = nettyChannel;
        unflushedWritesListener = new AtomicReference(new MultipleFutureListener(nettyChannel.newPromise()));
    }

    @Override
    public Observable writeAndFlush(O msg) {
        write(msg);
        return flush();
    }

    @Override
    public  Observable writeAndFlush(final R msg, final ContentTransformer transformer) {
        write(msg, transformer);
        return flush();
    }

    @Override
    public void write(O msg) {
        writeOnChannel(msg);
    }

    @Override
    public  void write(R msg, ContentTransformer transformer) {
        ByteBuf contentBytes = transformer.call(msg, getAllocator());
        writeOnChannel(contentBytes);
    }

    @Override
    public void writeBytes(byte[] msg) {
        write(msg, new ByteTransformer());
    }

    @Override
    public void writeString(String msg) {
        write(msg, new StringTransformer());
    }

    @Override
    public Observable writeBytesAndFlush(byte[] msg) {
        write(msg, new ByteTransformer());
        return flush();
    }

    @Override
    public Observable writeStringAndFlush(String msg) {
        write(msg, new StringTransformer());
        return flush();
    }
    
    @Override
    public void writeFileRegion(FileRegion region) {
        writeOnChannel(region);
    }

    @Override
    @SuppressWarnings("unchecked")
    public Observable flush() {
        final long startTimeMillis = Clock.newStartTimeMillis();
        eventsSubject.onEvent(metricEventProvider.getFlushStartEvent());
        MultipleFutureListener existingListener =
                unflushedWritesListener.getAndSet(new MultipleFutureListener(nettyChannel.newPromise()));
        /**
         * Do flush() after getting the last listener so that we do not wait for a write which is not flushed.
         * If we do it before getting the existingListener then the write that happens after the flush() from the user
         * will be contained in the retrieved listener and hence we will wait till the next flush() finish.
         */
        nettyChannel.flush();
        return existingListener.asObservable()
                               .doOnCompleted(new Action0() {
                                   @Override
                                   public void call() {
                                       eventsSubject.onEvent(metricEventProvider.getFlushSuccessEvent(),
                                                             Clock.onEndMillis(startTimeMillis));
                                   }
                               })
                               .doOnError(new Action1() {
                                   @Override
                                   public void call(Throwable throwable) {
                                       eventsSubject.onEvent(metricEventProvider.getFlushFailedEvent(),
                                                             Clock.onEndMillis(startTimeMillis), throwable);
                                   }
                               });
    }

    @Override
    public void cancelPendingWrites(boolean mayInterruptIfRunning) {
        unflushedWritesListener.get().cancelPendingFutures(mayInterruptIfRunning);
    }

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

    protected ChannelFuture writeOnChannel(Object msg) {
        ChannelFuture writeFuture = getChannel().write(msg); // Calling write on context will be wrong as the context will be of a component not necessarily, the tail of the pipeline.
        unflushedWritesListener.get().listen(writeFuture);
        return writeFuture;
    }

    public Channel getChannel() {
        return nettyChannel;
    }

    public boolean isCloseIssued() {
        return closeIssued.get();
    }

    @Override
    public Observable close() {
        return close(false);
    }

    @Override
    public Observable close(boolean flush) {
        if (closeIssued.compareAndSet(false, true)) {
            return _close(flush);
        } else {
            return CONNECTION_ALREADY_CLOSED;
        }
    }

    protected Observable _close(boolean flush) {
        return Observable.empty();
    }

}