/*
 * ====================================================================
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF 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.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */
package org.apache.hc.core5.http.nio.support;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.util.List;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicReference;

import org.apache.hc.core5.concurrent.FutureCallback;
import org.apache.hc.core5.http.EntityDetails;
import org.apache.hc.core5.http.Header;
import org.apache.hc.core5.http.HttpException;
import org.apache.hc.core5.http.HttpResponse;
import org.apache.hc.core5.http.HttpStatus;
import org.apache.hc.core5.http.nio.AsyncClientExchangeHandler;
import org.apache.hc.core5.http.nio.AsyncRequestProducer;
import org.apache.hc.core5.http.nio.AsyncResponseConsumer;
import org.apache.hc.core5.http.nio.CapacityChannel;
import org.apache.hc.core5.http.nio.DataStreamChannel;
import org.apache.hc.core5.http.nio.RequestChannel;
import org.apache.hc.core5.http.protocol.HttpContext;
import org.apache.hc.core5.util.Args;

/**
 * Basic {@link AsyncClientExchangeHandler} implementation that makes use
 * of {@link AsyncRequestProducer} to generate request message
 * and {@link AsyncResponseConsumer} to process the response message returned by the server.
 *
 * @param <T> The result type.
 * @since 5.5
 */
public abstract class AbstractClientExchangeHandler<T> implements AsyncClientExchangeHandler {

    private final AsyncRequestProducer requestProducer;
    private final AtomicReference<AsyncResponseConsumer<T>> responseConsumerRef;
    private final AtomicBoolean completed;
    private final AtomicBoolean outputTerminated;
    private final FutureCallback<T> resultCallback;

    public AbstractClientExchangeHandler(
            final AsyncRequestProducer requestProducer,
            final FutureCallback<T> resultCallback) {
        this.requestProducer = Args.notNull(requestProducer, "Request producer");
        this.responseConsumerRef = new AtomicReference<>();
        this.completed = new AtomicBoolean();
        this.resultCallback = resultCallback;
        this.outputTerminated = new AtomicBoolean();
    }

    @Override
    public void produceRequest(final RequestChannel requestChannel, final HttpContext httpContext) throws HttpException, IOException {
        requestProducer.sendRequest(requestChannel, httpContext);
    }

    @Override
    public int available() {
        return requestProducer.available();
    }

    @Override
    public void produce(final DataStreamChannel channel) throws IOException {
        if (outputTerminated.get()) {
            channel.endStream();
            return;
        }
        requestProducer.produce(channel);
    }

    @Override
    public void consumeInformation(final HttpResponse response, final HttpContext httpContext) throws HttpException, IOException {
    }

    /**
     * Triggered to supply a response consumer to process the incoming response.
     * @param response the response message.
     * @param entityDetails the request entity details.
     * @param context the actual execution context.
     * @return the request consumer.
     * @throws HttpException in case of an HTTP protocol violation.
     */
    protected abstract AsyncResponseConsumer<T> supplyConsumer(
            HttpResponse response,
            EntityDetails entityDetails,
            HttpContext context) throws HttpException;


    @Override
    public void consumeResponse(final HttpResponse response, final EntityDetails entityDetails, final HttpContext httpContext) throws HttpException, IOException {
        if (response.getCode() >= HttpStatus.SC_CLIENT_ERROR) {
            releaseRequestProducer();
        }
        final AsyncResponseConsumer<T> responseConsumer = supplyConsumer(response, entityDetails, httpContext);
        if (responseConsumer == null) {
            throw new HttpException("Unable to process response");
        }
        responseConsumerRef.set(responseConsumer);
        responseConsumerRef.get().consumeResponse(response, entityDetails, httpContext, new FutureCallback<T>() {

            @Override
            public void completed(final T result) {
                completedInternal(result);
            }

            @Override
            public void failed(final Exception ex) {
                failedInternal(ex);
            }

            @Override
            public void cancelled() {
                cancelledInternal();
            }

        });
    }

    @Override
    public void cancel() {
        cancelledInternal();
    }

    @Override
    public void updateCapacity(final CapacityChannel capacityChannel) throws IOException {
        final AsyncResponseConsumer<T> responseConsumer = responseConsumerRef.get();
        if (responseConsumer != null) {
            responseConsumer.updateCapacity(capacityChannel);
        } else {
            capacityChannel.update(Integer.MAX_VALUE);
        }
    }

    @Override
    public void consume(final ByteBuffer src) throws IOException {
        final AsyncResponseConsumer<T> responseConsumer = responseConsumerRef.get();
        if (responseConsumer != null) {
            responseConsumer.consume(src);
        }
    }

    @Override
    public void streamEnd(final List<? extends Header> trailers) throws HttpException, IOException {
        final AsyncResponseConsumer<T> responseConsumer = responseConsumerRef.get();
        if (responseConsumer != null) {
            responseConsumer.streamEnd(trailers);
        }
    }

    @Override
    public void failed(final Exception cause) {
        try {
            final AsyncResponseConsumer<T> responseConsumer = responseConsumerRef.getAndSet(null);
            if (responseConsumer != null) {
                try {
                    responseConsumer.failed(cause);
                } finally {
                    responseConsumer.releaseResources();
                }
            }
            if (outputTerminated.compareAndSet(false, true)) {
                requestProducer.failed(cause);
                requestProducer.releaseResources();
            }
        } finally {
            failedInternal(cause);
        }
    }

    private void completedInternal(final T result) {
        if (completed.compareAndSet(false, true)) {
            try {
                if (resultCallback != null) {
                    resultCallback.completed(result);
                }
            } finally {
                releaseResourcesInternal();
            }
        }
    }

    private void failedInternal(final Exception ex) {
        if (completed.compareAndSet(false, true)) {
            try {
                if (resultCallback != null) {
                    resultCallback.failed(ex);
                }
            } finally {
                releaseResourcesInternal();
            }
        }
    }

    private void cancelledInternal() {
        if (completed.compareAndSet(false, true)) {
            try {
                if (resultCallback != null) {
                    resultCallback.cancelled();
                }
            } finally {
                releaseResourcesInternal();
            }
        }
    }

    private void releaseResponseConsumer() {
        final AsyncResponseConsumer<T> responseConsumer = responseConsumerRef.getAndSet(null);
        if (responseConsumer != null) {
            responseConsumer.releaseResources();
        }
    }

    private void releaseRequestProducer() {
        if (outputTerminated.compareAndSet(false, true)) {
            requestProducer.releaseResources();
        }
    }

    private void releaseResourcesInternal() {
        releaseRequestProducer();
        releaseResponseConsumer();
    }

    @Override
    public void releaseResources() {
        // Note even though the message exchange has been fully
        // completed on the transport level, the response
        // consumer may still be busy consuming and digesting
        // the response message
        releaseRequestProducer();
    }

}
